diff --git a/core/deno.json b/core/deno.json
index 64cce4a3..a7270a7d 100644
--- a/core/deno.json
+++ b/core/deno.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/nats-core",
-  "version": "3.0.0-29",
+  "version": "3.0.0-30",
   "exports": {
     ".": "./src/mod.ts",
     "./internal": "./src/internal_mod.ts"
diff --git a/core/package.json b/core/package.json
index 3e7bed37..28eccbb1 100644
--- a/core/package.json
+++ b/core/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/nats-core",
-  "version": "3.0.0-29",
+  "version": "3.0.0-30",
   "files": [
     "lib/",
     "LICENSE",
diff --git a/core/src/codec.ts b/core/src/codec.ts
index 283adfe8..705e666a 100644
--- a/core/src/codec.ts
+++ b/core/src/codec.ts
@@ -13,9 +13,6 @@
  * limitations under the License.
  */
 
-import { TD, TE } from "./encoders.ts";
-import { ErrorCode, NatsError } from "./core.ts";
-
 export interface Codec<T> {
   /**
    * Encode T to an Uint8Array suitable for including in a message payload.
@@ -29,50 +26,3 @@ export interface Codec<T> {
    */
   decode(a: Uint8Array): T;
 }
-
-/**
- * Returns a {@link Codec} for encoding strings to a message payload
- * and decoding message payloads into strings.
- */
-export function StringCodec(): Codec<string> {
-  return {
-    encode(d: string): Uint8Array {
-      return TE.encode(d);
-    },
-    decode(a: Uint8Array): string {
-      return TD.decode(a);
-    },
-  };
-}
-
-/**
- * Returns a {@link Codec}  for encoding JavaScript object to JSON and
- * serialize them to an Uint8Array, and conversely, from an
- * Uint8Array to JSON to a JavaScript Object.
- * @param reviver
- */
-export function JSONCodec<T = unknown>(
-  reviver?: (this: unknown, key: string, value: unknown) => unknown,
-): Codec<T> {
-  return {
-    encode(d: T): Uint8Array {
-      try {
-        if (d === undefined) {
-          // @ts-ignore: json will not handle undefined
-          d = null;
-        }
-        return TE.encode(JSON.stringify(d));
-      } catch (err) {
-        throw NatsError.errorForCode(ErrorCode.BadJson, err as Error);
-      }
-    },
-
-    decode(a: Uint8Array): T {
-      try {
-        return JSON.parse(TD.decode(a), reviver);
-      } catch (err) {
-        throw NatsError.errorForCode(ErrorCode.BadJson, err as Error);
-      }
-    },
-  };
-}
diff --git a/core/src/internal_mod.ts b/core/src/internal_mod.ts
index 418f7e24..8520ac61 100644
--- a/core/src/internal_mod.ts
+++ b/core/src/internal_mod.ts
@@ -65,7 +65,6 @@ export {
   usernamePasswordAuthenticator,
 } from "./authenticator.ts";
 export type { Codec } from "./codec.ts";
-export { JSONCodec, StringCodec } from "./codec.ts";
 export * from "./nkeys.ts";
 export { QueuedIteratorImpl } from "./queued_iterator.ts";
 export type { MsgArg, ParserEvent } from "./parser.ts";
diff --git a/core/src/mod.ts b/core/src/mod.ts
index 06d0bc81..e5a48bdb 100644
--- a/core/src/mod.ts
+++ b/core/src/mod.ts
@@ -28,7 +28,6 @@ export {
   ErrorCode,
   Events,
   headers,
-  JSONCodec,
   jwtAuthenticator,
   Match,
   Metric,
@@ -41,7 +40,6 @@ export {
   Nuid,
   nuid,
   RequestStrategy,
-  StringCodec,
   syncIterator,
   tokenAuthenticator,
   usernamePasswordAuthenticator,
diff --git a/core/src/msg.ts b/core/src/msg.ts
index 6598cf86..9d5aef65 100644
--- a/core/src/msg.ts
+++ b/core/src/msg.ts
@@ -15,11 +15,10 @@
 import { MsgHdrsImpl } from "./headers.ts";
 import type { MsgArg } from "./parser.ts";
 import { Empty, TD } from "./encoders.ts";
-import type { Codec } from "./codec.ts";
-import { JSONCodec } from "./codec.ts";
 import type {
   Msg,
   MsgHdrs,
+  Payload,
   Publisher,
   RequestInfo,
   ReviverFn,
@@ -43,7 +42,6 @@ export class MsgImpl implements Msg {
   _reply!: string;
   _subject!: string;
   publisher: Publisher;
-  static jc: Codec<unknown>;
 
   constructor(msg: MsgArg, data: Uint8Array, publisher: Publisher) {
     this._msg = msg;
@@ -90,7 +88,7 @@ export class MsgImpl implements Msg {
 
   // eslint-ignore-next-line @typescript-eslint/no-explicit-any
   respond(
-    data: Uint8Array = Empty,
+    data: Payload = Empty,
     opts?: { headers?: MsgHdrs; reply?: string },
   ): boolean {
     if (this.reply) {
@@ -108,7 +106,7 @@ export class MsgImpl implements Msg {
   }
 
   json<T = unknown>(reviver?: ReviverFn): T {
-    return JSONCodec<T>(reviver).decode(this.data);
+    return JSON.parse(this.string(), reviver);
   }
 
   string(): string {
diff --git a/core/src/version.ts b/core/src/version.ts
index 7cef50e1..14911460 100644
--- a/core/src/version.ts
+++ b/core/src/version.ts
@@ -1,2 +1,2 @@
 // This file is generated - do not edit
-export const version = "3.0.0-29";
+export const version = "3.0.0-30";
diff --git a/core/tests/auth_test.ts b/core/tests/auth_test.ts
index 38369f45..89c1dd1d 100644
--- a/core/tests/auth_test.ts
+++ b/core/tests/auth_test.ts
@@ -48,7 +48,6 @@ import {
   jwtAuthenticator,
   nkeyAuthenticator,
   nkeys,
-  StringCodec,
   tokenAuthenticator,
   usernamePasswordAuthenticator,
 } from "../src/internal_mod.ts";
@@ -487,8 +486,7 @@ Deno.test("auth - creds authenticator validation", () => {
     `eyJ0eXAiOiJqd3QiLCJhbGciOiJlZDI1NTE5In0.eyJqdGkiOiJFU1VQS1NSNFhGR0pLN0FHUk5ZRjc0STVQNTZHMkFGWERYQ01CUUdHSklKUEVNUVhMSDJBIiwiaWF0IjoxNTQ0MjE3NzU3LCJpc3MiOiJBQ1pTV0JKNFNZSUxLN1FWREVMTzY0VlgzRUZXQjZDWENQTUVCVUtBMzZNSkpRUlBYR0VFUTJXSiIsInN1YiI6IlVBSDQyVUc2UFY1NTJQNVNXTFdUQlAzSDNTNUJIQVZDTzJJRUtFWFVBTkpYUjc1SjYzUlE1V002IiwidHlwZSI6InVzZXIiLCJuYXRzIjp7InB1YiI6e30sInN1YiI6e319fQ.kCR9Erm9zzux4G6M-V2bp7wKMKgnSNqMBACX05nwePRWQa37aO_yObbhcJWFGYjo1Ix-oepOkoyVLxOJeuD8Bw`;
   const ukp = nkeys.createUser();
   const upk = ukp.getPublicKey();
-  const sc = StringCodec();
-  const seed = sc.decode(ukp.getSeed());
+  const seed = new TextDecoder().decode(ukp.getSeed());
 
   function creds(ajwt = "", aseed = ""): string {
     return `-----BEGIN NATS USER JWT-----
@@ -513,7 +511,7 @@ Deno.test("auth - creds authenticator validation", () => {
   tests.push([jwt, seed, true, "jwt and seed"]);
 
   tests.forEach((v) => {
-    const d = sc.encode(creds(v[0], v[1]));
+    const d = new TextEncoder().encode(creds(v[0], v[1]));
     try {
       const auth = credsAuthenticator(d);
       if (!v[2]) {
diff --git a/core/tests/basics_test.ts b/core/tests/basics_test.ts
index 487c561b..38c16f78 100644
--- a/core/tests/basics_test.ts
+++ b/core/tests/basics_test.ts
@@ -34,10 +34,8 @@ import {
   Feature,
   headers,
   isIP,
-  JSONCodec,
   nuid,
   RequestStrategy,
-  StringCodec,
   syncIterator,
 } from "../src/internal_mod.ts";
 import type {
@@ -238,7 +236,6 @@ Deno.test("basics - wildcard subscriptions", async () => {
 
 Deno.test("basics - correct data in message", async () => {
   const { ns, nc } = await _setup(connect);
-  const sc = StringCodec();
   const subj = createInbox();
   const mp = deferred<Msg>();
   const sub = nc.subscribe(subj);
@@ -249,10 +246,10 @@ Deno.test("basics - correct data in message", async () => {
     }
   })().then();
 
-  nc.publish(subj, sc.encode(subj));
+  nc.publish(subj, subj);
   const m = await mp;
   assertEquals(m.subject, subj);
-  assertEquals(sc.decode(m.data), subj);
+  assertEquals(m.string(), subj);
   assertEquals(m.reply, "");
   await cleanup(ns, nc);
 });
@@ -359,16 +356,15 @@ Deno.test("basics - unsubscribe stops messages", async () => {
 
 Deno.test("basics - request", async () => {
   const { ns, nc } = await _setup(connect);
-  const sc = StringCodec();
   const s = createInbox();
   const sub = nc.subscribe(s);
   (async () => {
     for await (const m of sub) {
-      m.respond(sc.encode("foo"));
+      m.respond("foo");
     }
   })().then();
   const msg = await nc.request(s);
-  assertEquals(sc.decode(msg.data), "foo");
+  assertEquals(msg.string(), "foo");
   await cleanup(ns, nc);
 });
 
@@ -415,10 +411,9 @@ Deno.test("basics - request cancel rejects", async () => {
 
 Deno.test("basics - old style requests", async () => {
   const { ns, nc } = await _setup(connect);
-  const sc = StringCodec();
   nc.subscribe("q", {
     callback: (_err, msg) => {
-      msg.respond(sc.encode("hello"));
+      msg.respond("hello");
     },
   });
 
@@ -427,7 +422,7 @@ Deno.test("basics - old style requests", async () => {
     Empty,
     { reply: "bar", noMux: true, timeout: 1000 },
   );
-  assertEquals("hello", sc.decode(m.data));
+  assertEquals("hello", m.string());
   assertEquals("bar", m.subject);
 
   await cleanup(ns, nc);
@@ -435,10 +430,9 @@ Deno.test("basics - old style requests", async () => {
 
 Deno.test("basics - request with custom subject", async () => {
   const { ns, nc } = await _setup(connect);
-  const sc = StringCodec();
   nc.subscribe("q", {
     callback: (_err, msg) => {
-      msg.respond(sc.encode("hello"));
+      msg.respond("hello");
     },
   });
 
@@ -459,13 +453,12 @@ Deno.test("basics - request with custom subject", async () => {
 
 Deno.test("basics - request with headers", async () => {
   const { ns, nc } = await _setup(connect);
-  const sc = StringCodec();
   const s = createInbox();
   const sub = nc.subscribe(s);
   (async () => {
     for await (const m of sub) {
       const headerContent = m.headers?.get("test-header");
-      m.respond(sc.encode(`header content: ${headerContent}`));
+      m.respond(`header content: ${headerContent}`);
     }
   })().then();
   const requestHeaders = headers();
@@ -474,19 +467,18 @@ Deno.test("basics - request with headers", async () => {
     headers: requestHeaders,
     timeout: 5000,
   });
-  assertEquals(sc.decode(msg.data), "header content: Hello, world!");
+  assertEquals(msg.string(), "header content: Hello, world!");
   await cleanup(ns, nc);
 });
 
 Deno.test("basics - request with headers and custom subject", async () => {
   const { ns, nc } = await _setup(connect);
-  const sc = StringCodec();
   const s = createInbox();
   const sub = nc.subscribe(s);
   (async () => {
     for await (const m of sub) {
       const headerContent = m.headers?.get("test-header");
-      m.respond(sc.encode(`header content: ${headerContent}`));
+      m.respond(`header content: ${headerContent}`);
     }
   })().then();
   const requestHeaders = headers();
@@ -497,7 +489,7 @@ Deno.test("basics - request with headers and custom subject", async () => {
     reply: "reply-subject",
     noMux: true,
   });
-  assertEquals(sc.decode(msg.data), "header content: Hello, world!");
+  assertEquals(msg.string(), "header content: Hello, world!");
   await cleanup(ns, nc);
 });
 
@@ -884,33 +876,31 @@ Deno.test("basics - create inbox", () => {
 
 Deno.test("basics - custom prefix", async () => {
   const { ns, nc } = await _setup(connect, {}, { inboxPrefix: "_x" });
-  const jc = JSONCodec();
   const subj = createInbox();
   nc.subscribe(subj, {
     max: 1,
     callback: (_err, msg) => {
-      msg.respond(jc.encode(msg.reply!.startsWith("_x.")));
+      msg.respond();
     },
   });
 
   const v = await nc.request(subj);
-  assert(jc.decode(v.data));
+  assert(v.subject.startsWith("_x."));
   await cleanup(ns, nc);
 });
 
 Deno.test("basics - custom prefix noMux", async () => {
   const { ns, nc } = await _setup(connect, {}, { inboxPrefix: "_y" });
-  const jc = JSONCodec();
   const subj = createInbox();
   nc.subscribe(subj, {
     max: 1,
     callback: (_err, msg) => {
-      msg.respond(jc.encode(msg.reply!.startsWith("_y.")));
+      msg.respond();
     },
   });
 
   const v = await nc.request(subj);
-  assert(jc.decode(v.data));
+  assert(v.subject.startsWith("_y."));
   await cleanup(ns, nc);
 });
 
@@ -1072,12 +1062,10 @@ Deno.test("basics - request many sentinel", async () => {
   const nci = nc as NatsConnectionImpl;
 
   const subj = createInbox();
-  const sc = StringCodec();
-  const payload = sc.encode("hello");
   nc.subscribe(subj, {
     callback: (_err, msg) => {
       for (let i = 0; i < 10; i++) {
-        msg.respond(payload);
+        msg.respond("hello");
       }
       msg.respond();
     },
@@ -1106,12 +1094,10 @@ Deno.test("basics - request many sentinel - partial response", async () => {
   const nci = nc as NatsConnectionImpl;
 
   const subj = createInbox();
-  const sc = StringCodec();
-  const payload = sc.encode("hello");
   nc.subscribe(subj, {
     callback: (_err, msg) => {
       for (let i = 0; i < 10; i++) {
-        msg.respond(payload);
+        msg.respond("hello");
       }
     },
   });
@@ -1217,8 +1203,7 @@ Deno.test("basics - info", async () => {
 Deno.test("basics - initial connect error", async () => {
   const listener = Deno.listen({ port: 0 });
   const port = (listener.addr as Deno.NetAddr).port;
-  const sc = StringCodec();
-  const INFO = sc.encode(
+  const INFO = new TextEncoder().encode(
     `INFO {"server_id":"FAKE","server_name":"FAKE","version":"2.9.4","proto":1,"go":"go1.19.2","host":"127.0.0.1","port":${port},"headers":true,"max_payload":1048576,"jetstream":true,"client_id":4,"client_ip":"127.0.0.1"}\r\n`,
   );
 
@@ -1283,14 +1268,8 @@ Deno.test("basics - msg typed payload", async () => {
   });
 
   assertEquals((await nc.request("echo", Empty)).string(), "");
-  assertEquals(
-    (await nc.request("echo", StringCodec().encode("hello"))).string(),
-    "hello",
-  );
-  assertEquals(
-    (await nc.request("echo", StringCodec().encode("5"))).string(),
-    "5",
-  );
+  assertEquals((await nc.request("echo", "hello")).string(), "hello");
+  assertEquals((await nc.request("echo", "5")).string(), "5");
 
   await assertRejects(
     async () => {
@@ -1298,32 +1277,24 @@ Deno.test("basics - msg typed payload", async () => {
       r.json<number>();
     },
     Error,
-    "Bad JSON",
+    "Unexpected end of JSON input",
   );
 
+  assertEquals((await nc.request("echo", JSON.stringify(null))).json(), null);
+  assertEquals((await nc.request("echo", JSON.stringify(5))).json(), 5);
   assertEquals(
-    (await nc.request("echo", JSONCodec().encode(null))).json(),
-    null,
-  );
-  assertEquals(
-    (await nc.request("echo", JSONCodec().encode(undefined))).json(),
-    null,
-  );
-  assertEquals((await nc.request("echo", JSONCodec().encode(5))).json(), 5);
-  assertEquals(
-    (await nc.request("echo", JSONCodec().encode("hello"))).json(),
+    (await nc.request("echo", JSON.stringify("hello"))).json(),
     "hello",
   );
+  assertEquals((await nc.request("echo", JSON.stringify(["hello"]))).json(), [
+    "hello",
+  ]);
   assertEquals(
-    (await nc.request("echo", JSONCodec().encode(["hello"]))).json(),
-    ["hello"],
-  );
-  assertEquals(
-    (await nc.request("echo", JSONCodec().encode({ one: "two" }))).json(),
+    (await nc.request("echo", JSON.stringify({ one: "two" }))).json(),
     { one: "two" },
   );
   assertEquals(
-    (await nc.request("echo", JSONCodec().encode([{ one: "two" }]))).json(),
+    (await nc.request("echo", JSON.stringify([{ one: "two" }]))).json(),
     [{ one: "two" }],
   );
 
@@ -1408,7 +1379,7 @@ Deno.test("basics - json reviver", async () => {
 
   nc.subscribe(subj, {
     callback: (_err, msg) => {
-      msg.respond(JSONCodec().encode({ date: Date.now(), auth: true }));
+      msg.respond(JSON.stringify({ date: Date.now(), auth: true }));
     },
   });
 
diff --git a/core/tests/codec_test.ts b/core/tests/codec_test.ts
deleted file mode 100644
index 0f8e1d1f..00000000
--- a/core/tests/codec_test.ts
+++ /dev/null
@@ -1,37 +0,0 @@
-/*
- * Copyright 2020-2023 The NATS Authors
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-import { JSONCodec, StringCodec } from "@nats-io/nats-core";
-import { assertEquals } from "jsr:@std/assert";
-
-Deno.test("codec - string", () => {
-  const sc = StringCodec();
-  const d = sc.encode("hello");
-  assertEquals(sc.decode(d), "hello");
-});
-
-Deno.test("codec - json", () => {
-  const sc = JSONCodec();
-  const o = { hello: "world" };
-  const d = sc.encode(o);
-  assertEquals(sc.decode(d), o);
-});
-
-Deno.test("codec - json w/ reviver", () => {
-  // deno-lint-ignore no-explicit-any
-  const sc = JSONCodec((k: string, v: any) => k === "time" ? new Date(v) : v);
-  const o = { time: new Date() };
-  const d = sc.encode(o);
-  assertEquals(sc.decode(d), o);
-});
diff --git a/core/tests/doublesubs_test.ts b/core/tests/doublesubs_test.ts
index aacba80b..a5cfa1de 100644
--- a/core/tests/doublesubs_test.ts
+++ b/core/tests/doublesubs_test.ts
@@ -20,7 +20,6 @@ import {
   Events,
   extend,
   headers,
-  StringCodec,
 } from "../src/internal_mod.ts";
 import type { NatsConnectionImpl } from "../src/internal_mod.ts";
 import { assertArrayIncludes, assertEquals } from "jsr:@std/assert";
@@ -77,7 +76,7 @@ async function runDoubleSubsTest(tls: boolean) {
   const bar = nc.subscribe("bar");
   const baz = nc.subscribe("baz");
   nc.publish("foo", Empty);
-  nc.publish("bar", StringCodec().encode("hello"));
+  nc.publish("bar", "hello");
   const h = headers();
   h.set("foo", "bar");
   nc.publish("baz", Empty, { headers: h });
diff --git a/core/tests/drain_test.ts b/core/tests/drain_test.ts
index 0c07bcfb..fe692945 100644
--- a/core/tests/drain_test.ts
+++ b/core/tests/drain_test.ts
@@ -13,7 +13,7 @@
  * limitations under the License.
  */
 import { assert, assertEquals, fail } from "jsr:@std/assert";
-import { createInbox, ErrorCode, StringCodec } from "../src/internal_mod.ts";
+import { createInbox, ErrorCode } from "../src/internal_mod.ts";
 import type { Msg, NatsError } from "../src/internal_mod.ts";
 import {
   assertThrowsAsyncErrorCode,
@@ -133,12 +133,11 @@ Deno.test("drain - reject reqrep during connection drain", async () => {
   const nc2 = await connect({ port: ns.port });
   const lock = Lock();
   const subj = createInbox();
-  const sc = StringCodec();
   // start a service for replies
   await nc.subscribe(subj, {
     callback: (_, msg: Msg) => {
       if (msg.reply) {
-        msg.respond(sc.encode("ok"));
+        msg.respond("ok");
       }
     },
   });
diff --git a/core/tests/headers_test.ts b/core/tests/headers_test.ts
index f4c4df6e..f104476d 100644
--- a/core/tests/headers_test.ts
+++ b/core/tests/headers_test.ts
@@ -23,7 +23,6 @@ import {
   MsgImpl,
   NatsError,
   Parser,
-  StringCodec,
 } from "../src/internal_mod.ts";
 import type {
   NatsConnectionImpl,
@@ -181,7 +180,7 @@ function status(code: number, description: string): Uint8Array {
     ? `NATS/1.0 ${code.toString()} ${description}`.trim()
     : "NATS/1.0";
   const line = `${status}\r\n\r\n\r\n`;
-  return StringCodec().encode(line);
+  return new TextEncoder().encode(line);
 }
 
 function checkStatus(code = 200, description = "") {
diff --git a/core/tests/json_test.ts b/core/tests/json_test.ts
index 0e3c49a1..86126948 100644
--- a/core/tests/json_test.ts
+++ b/core/tests/json_test.ts
@@ -14,27 +14,14 @@
  */
 import { connect } from "./connect.ts";
 import { assertEquals } from "jsr:@std/assert";
-import { createInbox, ErrorCode, JSONCodec } from "../src/internal_mod.ts";
+import { createInbox } from "../src/internal_mod.ts";
 import type { Msg, NatsError } from "../src/internal_mod.ts";
 import { Lock } from "test_helpers";
-import { assertThrowsErrorCode } from "../../test_helpers/asserts.ts";
 import { _setup, cleanup } from "test_helpers";
 
-Deno.test("json - bad json error in callback", () => {
-  const o = {};
-  //@ts-ignore: bad json
-  o.a = o;
-
-  const jc = JSONCodec();
-  assertThrowsErrorCode(() => {
-    jc.encode(o);
-  }, ErrorCode.BadJson);
-});
-
 function macro(input: unknown) {
   return async () => {
     const { ns, nc } = await _setup(connect);
-    const jc = JSONCodec();
     const lock = Lock();
     const subj = createInbox();
     nc.subscribe(subj, {
@@ -44,13 +31,13 @@ function macro(input: unknown) {
         if (input === undefined) {
           input = null;
         }
-        assertEquals(jc.decode(msg.data), input);
+        assertEquals(msg.json(), input);
         lock.unlock();
       },
       max: 1,
     });
 
-    nc.publish(subj, jc.encode(input));
+    nc.publish(subj, JSON.stringify(input));
     await nc.flush();
     await lock;
     await cleanup(ns, nc);
@@ -60,7 +47,6 @@ function macro(input: unknown) {
 Deno.test("json - string", macro("helloworld"));
 Deno.test("json - empty", macro(""));
 Deno.test("json - null", macro(null));
-Deno.test("json - undefined", macro(undefined));
 Deno.test("json - number", macro(10));
 Deno.test("json - false", macro(false));
 Deno.test("json - true", macro(true));
diff --git a/core/tests/mrequest_test.ts b/core/tests/mrequest_test.ts
index 5389e63f..01f24603 100644
--- a/core/tests/mrequest_test.ts
+++ b/core/tests/mrequest_test.ts
@@ -22,7 +22,6 @@ import {
   Empty,
   Events,
   RequestStrategy,
-  StringCodec,
 } from "../src/internal_mod.ts";
 
 import { assert, assertEquals, assertRejects, fail } from "jsr:@std/assert";
@@ -118,12 +117,10 @@ async function requestManySentinel(
   const nci = nc as NatsConnectionImpl;
 
   const subj = createInbox();
-  const sc = StringCodec();
-  const payload = sc.encode("hello");
   nc.subscribe(subj, {
     callback: (_err, msg) => {
       for (let i = 0; i < 10; i++) {
-        msg.respond(payload);
+        msg.respond("hello");
       }
       if (!partial) {
         msg.respond();
diff --git a/core/tests/types_test.ts b/core/tests/types_test.ts
index eedac8da..61a26c33 100644
--- a/core/tests/types_test.ts
+++ b/core/tests/types_test.ts
@@ -15,13 +15,7 @@
 
 import { connect } from "./connect.ts";
 import type { Msg, NatsConnection } from "../src/internal_mod.ts";
-import {
-  createInbox,
-  DataBuffer,
-  deferred,
-  JSONCodec,
-  StringCodec,
-} from "../src/internal_mod.ts";
+import { createInbox, DataBuffer, deferred } from "../src/internal_mod.ts";
 import { assert, assertEquals } from "jsr:@std/assert";
 import { NatsServer } from "../../test_helpers/launcher.ts";
 
@@ -38,27 +32,25 @@ function mh(nc: NatsConnection, subj: string): Promise<Msg> {
 
 Deno.test("types - json types", async () => {
   const ns = await NatsServer.start();
-  const jc = JSONCodec();
   const nc = await connect({ port: ns.port });
   const subj = createInbox();
   const dm = mh(nc, subj);
-  nc.publish(subj, jc.encode(6691));
+  nc.publish(subj, JSON.stringify(6691));
   const msg = await dm;
-  assertEquals(typeof jc.decode(msg.data), "number");
-  assertEquals(jc.decode(msg.data), 6691);
+  assertEquals(typeof msg.json(), "number");
+  assertEquals(msg.json<number>(), 6691);
   await nc.close();
   await ns.stop();
 });
 
 Deno.test("types - string types", async () => {
   const ns = await NatsServer.start();
-  const sc = StringCodec();
   const nc = await connect({ port: ns.port });
   const subj = createInbox();
   const dm = mh(nc, subj);
-  nc.publish(subj, sc.encode("hello world"));
+  nc.publish(subj, "hello world");
   const msg = await dm;
-  assertEquals(sc.decode(msg.data), "hello world");
+  assertEquals(msg.string(), "hello world");
   await nc.close();
   await ns.stop();
 });
diff --git a/jetstream/deno.json b/jetstream/deno.json
index 7533229d..098cfe63 100644
--- a/jetstream/deno.json
+++ b/jetstream/deno.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/jetstream",
-  "version": "3.0.0-14",
+  "version": "3.0.0-15",
   "exports": {
     ".": "./src/mod.ts",
     "./internal": "./src/internal_mod.ts"
@@ -33,6 +33,6 @@
     "test": "deno test -A --parallel --reload --trace-leaks --quiet tests/ --import-map=import_map.json"
   },
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29"
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30"
   }
 }
diff --git a/jetstream/import_map.json b/jetstream/import_map.json
index f09e94e2..bafe819c 100644
--- a/jetstream/import_map.json
+++ b/jetstream/import_map.json
@@ -2,8 +2,8 @@
   "imports": {
     "@nats-io/nkeys": "jsr:@nats-io/nkeys@1.2.0-4",
     "@nats-io/nuid": "jsr:@nats-io/nuid@2.0.1-2",
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
-    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-29/internal",
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
+    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-30/internal",
     "test_helpers": "../test_helpers/mod.ts",
     "@std/io": "jsr:@std/io@0.224.0"
   }
diff --git a/jetstream/package.json b/jetstream/package.json
index 09c21942..f75421ff 100644
--- a/jetstream/package.json
+++ b/jetstream/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/jetstream",
-  "version": "3.0.0-14",
+  "version": "3.0.0-15",
   "files": [
     "lib/",
     "LICENSE",
@@ -34,7 +34,7 @@
   },
   "description": "jetstream library - this library implements all the base functionality for NATS JetStream for javascript clients",
   "dependencies": {
-    "@nats-io/nats-core": "~3.0.0-29"
+    "@nats-io/nats-core": "~3.0.0-30"
   },
   "devDependencies": {
     "@types/node": "^22.7.6",
diff --git a/jetstream/src/consumer.ts b/jetstream/src/consumer.ts
index 42fc347e..9f98ddb6 100644
--- a/jetstream/src/consumer.ts
+++ b/jetstream/src/consumer.ts
@@ -553,7 +553,7 @@ export class PullConsumerMessagesImpl extends QueuedIteratorImpl<JsMsg>
     this._push(() => {
       nc.publish(
         subj,
-        this.consumer.api.jc.encode(opts),
+        JSON.stringify(opts),
         { reply: this.inbox },
       );
       this.notify(ConsumerDebugEvents.Next, opts);
diff --git a/jetstream/src/jsbaseclient_api.ts b/jetstream/src/jsbaseclient_api.ts
index 776ba895..4badfa40 100644
--- a/jetstream/src/jsbaseclient_api.ts
+++ b/jetstream/src/jsbaseclient_api.ts
@@ -19,10 +19,8 @@ import {
   Empty,
   ErrorCode,
   extend,
-  JSONCodec,
 } from "@nats-io/nats-core/internal";
 import type {
-  Codec,
   Msg,
   NatsConnection,
   NatsConnectionImpl,
@@ -58,7 +56,6 @@ export class BaseApiClientImpl {
   opts: JetStreamOptions;
   prefix: string;
   timeout: number;
-  jc: Codec<unknown>;
 
   constructor(nc: NatsConnection, opts?: JetStreamOptions) {
     this.nc = nc as NatsConnectionImpl;
@@ -66,7 +63,6 @@ export class BaseApiClientImpl {
     this._parseOpts();
     this.prefix = this.opts.apiPrefix!;
     this.timeout = this.opts.timeout!;
-    this.jc = JSONCodec();
   }
 
   getOptions(): JetStreamOptions {
@@ -95,7 +91,7 @@ export class BaseApiClientImpl {
 
     let a: Uint8Array = Empty;
     if (data) {
-      a = this.jc.encode(data);
+      a = new TextEncoder().encode(JSON.stringify(data));
     }
 
     let { retries } = opts as {
@@ -143,7 +139,7 @@ export class BaseApiClientImpl {
   }
 
   parseJsResponse(m: Msg): unknown {
-    const v = this.jc.decode(m.data);
+    const v = JSON.parse(new TextDecoder().decode(m.data));
     const r = v as ApiResponse;
     if (r.error) {
       const err = checkJsErrorCode(r.error.code, r.error.description);
diff --git a/jetstream/src/jsm.ts b/jetstream/src/jsm.ts
index 6eec8bf1..9cf213c9 100644
--- a/jetstream/src/jsm.ts
+++ b/jetstream/src/jsm.ts
@@ -31,7 +31,6 @@ import type {
 } from "@nats-io/nats-core";
 import {
   Empty,
-  JSONCodec,
   QueuedIteratorImpl,
   RequestStrategy,
   TD,
@@ -62,7 +61,7 @@ export class DirectStreamAPIImpl extends BaseApiClientImpl
       qq = null;
     }
 
-    const payload = qq ? this.jc.encode(qq) : Empty;
+    const payload = qq ? JSON.stringify(qq) : Empty;
     const pre = this.opts.apiPrefix || "$JS.API";
     const subj = last_by_subj
       ? `${pre}.DIRECT.GET.${stream}.${last_by_subj}`
@@ -184,7 +183,7 @@ export class DirectMsgImpl implements DirectMsg {
   }
 
   json<T = unknown>(reviver?: ReviverFn): T {
-    return JSONCodec<T>(reviver).decode(this.data);
+    return JSON.parse(new TextDecoder().decode(this.data), reviver);
   }
 
   string(): string {
diff --git a/jetstream/src/jsmsg.ts b/jetstream/src/jsmsg.ts
index 9acb29e8..c16d06fc 100644
--- a/jetstream/src/jsmsg.ts
+++ b/jetstream/src/jsmsg.ts
@@ -24,10 +24,8 @@ import type {
 import {
   DataBuffer,
   deferred,
-  JSONCodec,
   nanos,
   RequestOne,
-  StringCodec,
 } from "@nats-io/nats-core/internal";
 import type { DeliveryInfo, PullOptions } from "./jsapi_types.ts";
 
@@ -280,9 +278,9 @@ export class JsMsgImpl implements JsMsg {
   }
 
   nak(millis?: number) {
-    let payload = NAK;
+    let payload: Uint8Array | string = NAK;
     if (millis) {
-      payload = StringCodec().encode(
+      payload = new TextEncoder().encode(
         `-NAK ${JSON.stringify({ delay: nanos(millis) })}`,
       );
     }
@@ -300,7 +298,7 @@ export class JsMsgImpl implements JsMsg {
     if (opts.expires && opts.expires > 0) {
       args.expires = nanos(opts.expires);
     }
-    const data = JSONCodec().encode(args);
+    const data = new TextEncoder().encode(JSON.stringify(args));
     const payload = DataBuffer.concat(NXT, SPACE, data);
     const reqOpts = subj ? { reply: subj } as RequestOptions : undefined;
     this.msg.respond(payload, reqOpts);
@@ -309,7 +307,7 @@ export class JsMsgImpl implements JsMsg {
   term(reason = "") {
     let term = TERM;
     if (reason?.length > 0) {
-      term = StringCodec().encode(`+TERM ${reason}`);
+      term = new TextEncoder().encode(`+TERM ${reason}`);
     }
     this.doAck(term);
   }
diff --git a/jetstream/src/jsmstream_api.ts b/jetstream/src/jsmstream_api.ts
index e989c656..547e0097 100644
--- a/jetstream/src/jsmstream_api.ts
+++ b/jetstream/src/jsmstream_api.ts
@@ -18,7 +18,6 @@ import {
   Empty,
   Feature,
   headers,
-  JSONCodec,
   MsgHdrsImpl,
   nanos,
   nuid,
@@ -695,7 +694,7 @@ export class StoredMsgImpl implements StoredMsg {
   }
 
   json<T = unknown>(reviver?: ReviverFn): T {
-    return JSONCodec<T>(reviver).decode(this.data);
+    return JSON.parse(new TextDecoder().decode(this.data), reviver);
   }
 
   string(): string {
diff --git a/jetstream/tests/fetch_test.ts b/jetstream/tests/fetch_test.ts
index fd3c414c..6ed15812 100644
--- a/jetstream/tests/fetch_test.ts
+++ b/jetstream/tests/fetch_test.ts
@@ -22,13 +22,7 @@ import {
 } from "test_helpers";
 import { initStream } from "./jstest_util.ts";
 import { assertEquals, assertExists, assertRejects } from "jsr:@std/assert";
-import {
-  delay,
-  Empty,
-  nanos,
-  StringCodec,
-  syncIterator,
-} from "@nats-io/nats-core";
+import { delay, Empty, nanos, syncIterator } from "@nats-io/nats-core";
 import type { NatsConnectionImpl } from "@nats-io/nats-core/internal";
 import {
   AckPolicy,
@@ -92,11 +86,10 @@ Deno.test("fetch - exactly messages", async () => {
   const { ns, nc } = await _setup(connect, jetstreamServerConf());
 
   const { stream, subj } = await initStream(nc);
-  const sc = StringCodec();
   const js = jetstream(nc);
   await Promise.all(
     new Array(200).fill("a").map((_, idx) => {
-      return js.publish(subj, sc.encode(`${idx}`));
+      return js.publish(subj, `${idx}`);
     }),
   );
 
diff --git a/jetstream/tests/jetstream_test.ts b/jetstream/tests/jetstream_test.ts
index 32399858..9a8c1f86 100644
--- a/jetstream/tests/jetstream_test.ts
+++ b/jetstream/tests/jetstream_test.ts
@@ -32,10 +32,8 @@ import {
   delay,
   Empty,
   headers,
-  JSONCodec,
   nanos,
   nuid,
-  StringCodec,
 } from "@nats-io/nats-core";
 import {
   assert,
@@ -216,16 +214,15 @@ Deno.test("jetstream - get message last by subject", async () => {
   await jsm.streams.add({ name: stream, subjects: [`${stream}.*`] });
 
   const js = jetstream(nc);
-  const sc = StringCodec();
-  await js.publish(`${stream}.A`, sc.encode("a"));
-  await js.publish(`${stream}.A`, sc.encode("aa"));
-  await js.publish(`${stream}.B`, sc.encode("b"));
-  await js.publish(`${stream}.B`, sc.encode("bb"));
+  await js.publish(`${stream}.A`, "a");
+  await js.publish(`${stream}.A`, "aa");
+  await js.publish(`${stream}.B`, "b");
+  await js.publish(`${stream}.B`, "bb");
 
   const sm = await jsm.streams.getMessage(stream, {
     last_by_subj: `${stream}.A`,
   });
-  assertEquals(sc.decode(sm.data), "aa");
+  assertEquals(sm.string(), "aa");
 
   await cleanup(ns, nc);
 });
@@ -334,11 +331,10 @@ Deno.test("jetstream - publish headers", async () => {
 Deno.test("jetstream - JSON", async () => {
   const { ns, nc } = await _setup(connect, jetstreamServerConf({}));
   const { stream, subj } = await initStream(nc);
-  const jc = JSONCodec();
   const js = jetstream(nc);
-  const values = [undefined, null, true, "", ["hello"], { hello: "world" }];
+  const values = [null, true, "", ["hello"], { hello: "world" }];
   for (const v of values) {
-    await js.publish(subj, jc.encode(v));
+    await js.publish(subj, JSON.stringify(v));
   }
 
   const jsm = await jetstreamManager(nc);
@@ -482,9 +478,8 @@ Deno.test("jetstream - seal", async () => {
   }
   const { stream, subj } = await initStream(nc);
   const js = jetstream(nc);
-  const sc = StringCodec();
-  await js.publish(subj, sc.encode("hello"));
-  await js.publish(subj, sc.encode("second"));
+  await js.publish(subj, "hello");
+  await js.publish(subj, "second");
 
   const jsm = await jetstreamManager(nc);
   const si = await jsm.streams.info(stream);
@@ -525,9 +520,8 @@ Deno.test("jetstream - deny delete", async () => {
   });
 
   const js = jetstream(nc);
-  const sc = StringCodec();
-  await js.publish(subj, sc.encode("hello"));
-  await js.publish(subj, sc.encode("second"));
+  await js.publish(subj, "hello");
+  await js.publish(subj, "second");
 
   const si = await jsm.streams.info(stream);
   assertEquals(si.config.deny_delete, true);
@@ -559,9 +553,8 @@ Deno.test("jetstream - deny purge", async () => {
   });
 
   const js = jetstream(nc);
-  const sc = StringCodec();
-  await js.publish(subj, sc.encode("hello"));
-  await js.publish(subj, sc.encode("second"));
+  await js.publish(subj, "hello");
+  await js.publish(subj, "second");
 
   const si = await jsm.streams.info(stream);
   assertEquals(si.config.deny_purge, true);
@@ -593,16 +586,15 @@ Deno.test("jetstream - rollup all", async () => {
   });
 
   const js = jetstream(nc);
-  const jc = JSONCodec();
   const buf = [];
   for (let i = 1; i < 11; i++) {
-    buf.push(js.publish(`${stream}.A`, jc.encode({ value: i })));
+    buf.push(js.publish(`${stream}.A`, JSON.stringify({ value: i })));
   }
   await Promise.all(buf);
 
   const h = headers();
   h.set(JsHeaders.RollupHdr, JsHeaders.RollupValueAll);
-  await js.publish(`${stream}.summary`, jc.encode({ value: 42 }), {
+  await js.publish(`${stream}.summary`, JSON.stringify({ value: 42 }), {
     headers: h,
   });
 
@@ -627,11 +619,10 @@ Deno.test("jetstream - rollup subject", async () => {
   });
 
   const js = jetstream(nc);
-  const jc = JSONCodec<Record<string, number>>();
   const buf = [];
   for (let i = 1; i < 11; i++) {
-    buf.push(js.publish(`${stream}.A`, jc.encode({ value: i })));
-    buf.push(js.publish(`${stream}.B`, jc.encode({ value: i })));
+    buf.push(js.publish(`${stream}.A`, JSON.stringify({ value: i })));
+    buf.push(js.publish(`${stream}.B`, JSON.stringify({ value: i })));
   }
   await Promise.all(buf);
 
@@ -647,7 +638,7 @@ Deno.test("jetstream - rollup subject", async () => {
 
   const h = headers();
   h.set(JsHeaders.RollupHdr, JsHeaders.RollupValueSubject);
-  await js.publish(`${stream}.A`, jc.encode({ value: 0 }), {
+  await js.publish(`${stream}.A`, JSON.stringify({ value: 0 }), {
     headers: h,
   });
 
@@ -684,10 +675,9 @@ Deno.test("jetstream - no rollup", async () => {
   assertEquals(si.config.allow_rollup_hdrs, false);
 
   const js = jetstream(nc);
-  const jc = JSONCodec<Record<string, number>>();
   const buf = [];
   for (let i = 1; i < 11; i++) {
-    buf.push(js.publish(`${stream}.A`, jc.encode({ value: i })));
+    buf.push(js.publish(`${stream}.A`, JSON.stringify({ value: i })));
   }
   await Promise.all(buf);
 
@@ -695,7 +685,7 @@ Deno.test("jetstream - no rollup", async () => {
   h.set(JsHeaders.RollupHdr, JsHeaders.RollupValueSubject);
   await assertRejects(
     async () => {
-      await js.publish(`${stream}.A`, jc.encode({ value: 42 }), {
+      await js.publish(`${stream}.A`, JSON.stringify({ value: 42 }), {
         headers: h,
       });
     },
@@ -936,8 +926,8 @@ Deno.test("jetstream - jsmsg decode", async () => {
     ack_policy: AckPolicy.Explicit,
   });
 
-  await js.publish("a.a", StringCodec().encode("hello"));
-  await js.publish("a.a", JSONCodec().encode({ one: "two", a: [1, 2, 3] }));
+  await js.publish("a.a", "hello");
+  await js.publish("a.a", JSON.stringify({ one: "two", a: [1, 2, 3] }));
 
   const c = await js.consumers.get(name, "me");
   assertEquals((await c.next())?.string(), "hello");
diff --git a/jetstream/tests/jsm_test.ts b/jetstream/tests/jsm_test.ts
index 45db99c9..a2ff776e 100644
--- a/jetstream/tests/jsm_test.ts
+++ b/jetstream/tests/jsm_test.ts
@@ -30,12 +30,10 @@ import {
   Empty,
   ErrorCode,
   headers,
-  JSONCodec,
   jwtAuthenticator,
   nanos,
   nkeys,
   nuid,
-  StringCodec,
 } from "@nats-io/nats-core";
 import type {
   ConsumerConfig,
@@ -736,24 +734,23 @@ Deno.test("jsm - get message", async () => {
   const { ns, nc } = await _setup(connect, jetstreamServerConf({}));
   const { stream, subj } = await initStream(nc);
 
-  const jc = JSONCodec();
   const h = headers();
   h.set("xxx", "a");
 
   const js = jetstream(nc);
-  await js.publish(subj, jc.encode(1), { headers: h });
-  await js.publish(subj, jc.encode(2));
+  await js.publish(subj, JSON.stringify(1), { headers: h });
+  await js.publish(subj, JSON.stringify(2));
 
   const jsm = await jetstreamManager(nc);
   let sm = await jsm.streams.getMessage(stream, { seq: 1 });
   assertEquals(sm.subject, subj);
   assertEquals(sm.seq, 1);
-  assertEquals(jc.decode(sm.data), 1);
+  assertEquals(sm.json<number>(), 1);
 
   sm = await jsm.streams.getMessage(stream, { seq: 2 });
   assertEquals(sm.subject, subj);
   assertEquals(sm.seq, 2);
-  assertEquals(jc.decode(sm.data), 2);
+  assertEquals(sm.json<number>(), 2);
 
   const err = await assertRejects(
     async () => {
@@ -773,9 +770,8 @@ Deno.test("jsm - get message payload", async () => {
   const { ns, nc } = await _setup(connect, jetstreamServerConf({}));
   const { stream, subj } = await initStream(nc);
   const js = jetstream(nc);
-  const sc = StringCodec();
   await js.publish(subj, Empty, { msgID: "empty" });
-  await js.publish(subj, sc.encode(""), { msgID: "empty2" });
+  await js.publish(subj, "", { msgID: "empty2" });
 
   const jsm = await jetstreamManager(nc);
   let sm = await jsm.streams.getMessage(stream, { seq: 1 });
@@ -787,7 +783,7 @@ Deno.test("jsm - get message payload", async () => {
   assertEquals(sm.subject, subj);
   assertEquals(sm.seq, 2);
   assertEquals(sm.data, Empty);
-  assertEquals(sc.decode(sm.data), "");
+  assertEquals(sm.string(), "");
 
   await cleanup(ns, nc);
 });
@@ -1200,14 +1196,12 @@ Deno.test("jsm - direct getMessage", async () => {
     allow_direct: true,
   });
 
-  const sc = StringCodec();
-
   const js = jetstream(nc);
-  await js.publish("foo", sc.encode("a"), { expect: { lastSequence: 0 } });
-  await js.publish("foo", sc.encode("b"), { expect: { lastSequence: 1 } });
-  await js.publish("foo", sc.encode("c"), { expect: { lastSequence: 2 } });
-  await js.publish("bar", sc.encode("d"), { expect: { lastSequence: 3 } });
-  await js.publish("foo", sc.encode("e"), { expect: { lastSequence: 4 } });
+  await js.publish("foo", "a", { expect: { lastSequence: 0 } });
+  await js.publish("foo", "b", { expect: { lastSequence: 1 } });
+  await js.publish("foo", "c", { expect: { lastSequence: 2 } });
+  await js.publish("bar", "d", { expect: { lastSequence: 3 } });
+  await js.publish("foo", "e", { expect: { lastSequence: 4 } });
 
   let m = await jsm.direct.getMessage("A", { seq: 0, next_by_subj: "bar" });
   assertEquals(m.seq, 4);
@@ -1953,8 +1947,8 @@ Deno.test("jsm - direct msg decode", async () => {
   const js = jetstream(nc);
   await jsm.streams.add({ name, subjects: [`a.>`], allow_direct: true });
 
-  await js.publish("a.a", StringCodec().encode("hello"));
-  await js.publish("a.a", JSONCodec().encode({ one: "two", a: [1, 2, 3] }));
+  await js.publish("a.a", "hello");
+  await js.publish("a.a", JSON.stringify({ one: "two", a: [1, 2, 3] }));
 
   assertEquals(
     (await jsm.direct.getMessage(name, { seq: 1 })).string(),
@@ -1975,8 +1969,8 @@ Deno.test("jsm - stored msg decode", async () => {
   const js = jetstream(nc);
   await jsm.streams.add({ name, subjects: [`a.>`], allow_direct: false });
 
-  await js.publish("a.a", StringCodec().encode("hello"));
-  await js.publish("a.a", JSONCodec().encode({ one: "two", a: [1, 2, 3] }));
+  await js.publish("a.a", "hello");
+  await js.publish("a.a", JSON.stringify({ one: "two", a: [1, 2, 3] }));
 
   assertEquals(
     (await jsm.streams.getMessage(name, { seq: 1 })).string(),
diff --git a/jetstream/tests/jsmsg_test.ts b/jetstream/tests/jsmsg_test.ts
index 0e9a2005..ab7c7090 100644
--- a/jetstream/tests/jsmsg_test.ts
+++ b/jetstream/tests/jsmsg_test.ts
@@ -20,7 +20,7 @@ import {
   StorageType,
 } from "../src/mod.ts";
 
-import { createInbox, Empty, nanos, StringCodec } from "@nats-io/nats-core";
+import { createInbox, Empty, nanos } from "@nats-io/nats-core";
 import type { Msg } from "@nats-io/nats-core";
 import type { MsgImpl } from "@nats-io/nats-core/internal";
 
@@ -133,7 +133,7 @@ Deno.test("jsmsg - acks", async () => {
   await nc.flush();
 
   assertEquals(replies.length, 4);
-  const sc = StringCodec();
+  const sc = new TextDecoder();
   assertEquals(sc.decode(replies[0].data), "-NAK");
   assertEquals(sc.decode(replies[1].data), "+WPI");
   assertEquals(sc.decode(replies[2].data), "+TERM");
diff --git a/jetstream/tests/streams_test.ts b/jetstream/tests/streams_test.ts
index 4bc7f411..25eb68d1 100644
--- a/jetstream/tests/streams_test.ts
+++ b/jetstream/tests/streams_test.ts
@@ -16,8 +16,6 @@
 import { connect, notCompatible } from "test_helpers";
 import { AckPolicy, jetstream, jetstreamManager } from "../src/mod.ts";
 
-import { JSONCodec } from "@nats-io/nats-core";
-
 import {
   assertEquals,
   assertExists,
@@ -67,7 +65,7 @@ Deno.test("streams - consumers", async () => {
 
   // add a stream and a message
   const { stream, subj } = await initStream(nc);
-  await js.publish(subj, JSONCodec().encode({ hello: "world" }));
+  await js.publish(subj, JSON.stringify({ hello: "world" }));
 
   // retrieve the stream
   const s = await js.streams.get(stream);
diff --git a/kv/deno.json b/kv/deno.json
index d537e6b4..dbbccd06 100644
--- a/kv/deno.json
+++ b/kv/deno.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/kv",
-  "version": "3.0.0-11",
+  "version": "3.0.0-12",
   "exports": {
     ".": "./src/mod.ts",
     "./internal": "./src/internal_mod.ts"
@@ -33,7 +33,7 @@
     "test": "deno test -A --parallel --reload --quiet tests/ --import-map=import_map.json"
   },
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
-    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-14"
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
+    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-15"
   }
 }
diff --git a/kv/import_map.json b/kv/import_map.json
index 0e765e3e..b0d4b9ee 100644
--- a/kv/import_map.json
+++ b/kv/import_map.json
@@ -1,9 +1,9 @@
 {
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
-    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-29/internal",
-    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-14",
-    "@nats-io/jetstream/internal": "jsr:@nats-io/jetstream@~3.0.0-14/internal",
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
+    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-30/internal",
+    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-15",
+    "@nats-io/jetstream/internal": "jsr:@nats-io/jetstream@~3.0.0-15/internal",
     "test_helpers": "../test_helpers/mod.ts",
     "@nats-io/nkeys": "jsr:@nats-io/nkeys@1.2.0-4",
     "@nats-io/nuid": "jsr:@nats-io/nuid@2.0.1-2",
diff --git a/kv/package.json b/kv/package.json
index c528b27b..2c9c691a 100644
--- a/kv/package.json
+++ b/kv/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/kv",
-  "version": "3.0.0-11",
+  "version": "3.0.0-12",
   "files": [
     "lib/",
     "LICENSE",
@@ -34,8 +34,8 @@
   },
   "description": "kv library - this library implements all the base functionality for NATS KV javascript clients",
   "dependencies": {
-    "@nats-io/jetstream": "~3.0.0-14",
-    "@nats-io/nats-core": "~3.0.0-29"
+    "@nats-io/jetstream": "~3.0.0-15",
+    "@nats-io/nats-core": "~3.0.0-30"
   },
   "devDependencies": {
     "@types/node": "^22.7.6",
diff --git a/kv/tests/kv_test.ts b/kv/tests/kv_test.ts
index 1ffe8a18..c004636b 100644
--- a/kv/tests/kv_test.ts
+++ b/kv/tests/kv_test.ts
@@ -71,7 +71,6 @@ import {
   NatsServer,
   notCompatible,
 } from "test_helpers";
-import { JSONCodec } from "@nats-io/nats-core/internal";
 import type { QueuedIteratorImpl } from "@nats-io/nats-core/internal";
 import { Kvm } from "../src/kv.ts";
 import { flakyTest } from "../../test_helpers/mod.ts";
@@ -1619,8 +1618,8 @@ Deno.test("kv - encoded entry", async () => {
   const js = jetstream(nc);
   const kv = await new Kvm(js).create("K");
   await kv.put("a", "hello");
-  await kv.put("b", JSONCodec().encode(5));
-  await kv.put("c", JSONCodec().encode(["hello", 5]));
+  await kv.put("b", JSON.stringify(5));
+  await kv.put("c", JSON.stringify(["hello", 5]));
 
   assertEquals((await kv.get("a"))?.string(), "hello");
   assertEquals((await kv.get("b"))?.json(), 5);
diff --git a/migration.md b/migration.md
index 23aba0b1..0dbefe9c 100644
--- a/migration.md
+++ b/migration.md
@@ -79,6 +79,11 @@ these modules for cross-runtime consumption.
   removed, these were supporting legacy JetStream APIs. If you were using these
   internal types to transform the types in the subscription, take a look at
   [messagepipeline](https://github.com/synadia-io/orbit.js/tree/main/messagepipeline).
+- The utilities `JSONCodec` and `StringCodec` have been removed, the `Msg` types
+  and derivatives can set string or Uint8Array payalods. To read payloads as
+  string or JSON use `string()` and `json()` methods. For publishing JSON
+  payloads, simply specify the output of `JSON.stringify()` to the publish
+  operation.
 
 ## Changes in JetStream
 
diff --git a/obj/deno.json b/obj/deno.json
index 3839b25c..42d2e23f 100644
--- a/obj/deno.json
+++ b/obj/deno.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/obj",
-  "version": "3.0.0-11",
+  "version": "3.0.0-12",
   "exports": {
     ".": "./src/mod.ts",
     "./internal": "./src/internal_mod.ts"
@@ -33,7 +33,7 @@
     "test": "deno test -A --parallel --reload --quiet tests/ --import-map=import_map.json"
   },
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
-    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-14"
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
+    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-15"
   }
 }
diff --git a/obj/import_map.json b/obj/import_map.json
index 0e765e3e..b0d4b9ee 100644
--- a/obj/import_map.json
+++ b/obj/import_map.json
@@ -1,9 +1,9 @@
 {
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
-    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-29/internal",
-    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-14",
-    "@nats-io/jetstream/internal": "jsr:@nats-io/jetstream@~3.0.0-14/internal",
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
+    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-30/internal",
+    "@nats-io/jetstream": "jsr:@nats-io/jetstream@~3.0.0-15",
+    "@nats-io/jetstream/internal": "jsr:@nats-io/jetstream@~3.0.0-15/internal",
     "test_helpers": "../test_helpers/mod.ts",
     "@nats-io/nkeys": "jsr:@nats-io/nkeys@1.2.0-4",
     "@nats-io/nuid": "jsr:@nats-io/nuid@2.0.1-2",
diff --git a/obj/package.json b/obj/package.json
index d5d70a07..8d228e52 100644
--- a/obj/package.json
+++ b/obj/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/obj",
-  "version": "3.0.0-11",
+  "version": "3.0.0-12",
   "files": [
     "lib/",
     "LICENSE",
@@ -34,8 +34,8 @@
   },
   "description": "obj library - this library implements all the base functionality for NATS objectstore for javascript clients",
   "dependencies": {
-    "@nats-io/jetstream": "~3.0.0-14",
-    "@nats-io/nats-core": "~3.0.0-29"
+    "@nats-io/jetstream": "~3.0.0-15",
+    "@nats-io/nats-core": "~3.0.0-30"
   },
   "devDependencies": {
     "@types/node": "^22.7.6",
diff --git a/obj/src/objectstore.ts b/obj/src/objectstore.ts
index f3d97729..f6c37c3b 100644
--- a/obj/src/objectstore.ts
+++ b/obj/src/objectstore.ts
@@ -25,7 +25,6 @@ import {
   deferred,
   Feature,
   headers,
-  JSONCodec,
   MsgHdrsImpl,
   nuid,
   QueuedIteratorImpl,
@@ -361,8 +360,7 @@ export class ObjectStoreImpl implements ObjectStore {
       const m = await this.jsm.streams.getMessage(this.stream, {
         last_by_subj: meta,
       });
-      const jc = JSONCodec<ServerObjectInfo>();
-      const soi = jc.decode(m.data) as ServerObjectInfo;
+      const soi = m.json<ServerObjectInfo>();
       soi.revision = m.seq;
       return soi;
     } catch (err) {
@@ -490,7 +488,7 @@ export class ObjectStoreImpl implements ObjectStore {
           h.set(JsHeaders.RollupHdr, JsHeaders.RollupValueSubject);
 
           // try to update the metadata
-          const pa = await this.js.publish(metaSubj, JSONCodec().encode(info), {
+          const pa = await this.js.publish(metaSubj, JSON.stringify(info), {
             headers: h,
             timeout,
           });
@@ -743,11 +741,10 @@ export class ObjectStoreImpl implements ObjectStore {
     info.chunks = 0;
     info.digest = "";
 
-    const jc = JSONCodec();
     const h = headers();
     h.set(JsHeaders.RollupHdr, JsHeaders.RollupValueSubject);
 
-    await this.js.publish(this._metaSubject(info.name), jc.encode(info), {
+    await this.js.publish(this._metaSubject(info.name), JSON.stringify(info), {
       headers: h,
     });
     return this.jsm.streams.purge(this.stream, {
diff --git a/obj/tests/objectstore_test.ts b/obj/tests/objectstore_test.ts
index bd00750f..85fafc58 100644
--- a/obj/tests/objectstore_test.ts
+++ b/obj/tests/objectstore_test.ts
@@ -35,7 +35,6 @@ import {
   nanos,
   nuid,
   SHA256,
-  StringCodec,
 } from "@nats-io/nats-core/internal";
 import type { NatsConnectionImpl } from "@nats-io/nats-core/internal";
 import type { ObjectInfo, ObjectStoreMeta } from "../src/types.ts";
@@ -216,8 +215,7 @@ Deno.test("objectstore - multi content", async () => {
     { name: "a.js", options: { max_chunk_size: 1 } },
     readableStreamFrom(a),
   );
-  const sc = StringCodec();
-  const b = sc.encode("hello world from object store");
+  const b = new TextEncoder().encode("hello world from object store");
   await os.put(
     { name: "b.js", options: { max_chunk_size: nc.info!.max_payload } },
     readableStreamFrom(b),
@@ -293,17 +291,15 @@ Deno.test("objectstore - multi with delete", async () => {
   const objm = new Objm(nc);
   const os = await objm.create("test", { storage: StorageType.Memory });
 
-  const sc = StringCodec();
-
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a!")),
+    readableStreamFrom(new TextEncoder().encode("a!")),
   );
 
   const si = await os.status({ subjects_filter: ">" });
   await os.put(
     { name: "b", options: { max_chunk_size: nc.info!.max_payload } },
-    readableStreamFrom(sc.encode("b!")),
+    readableStreamFrom(new TextEncoder().encode("b!")),
   );
 
   await os.get("b");
@@ -323,14 +319,31 @@ Deno.test("objectstore - object names", async () => {
   }
   const objm = new Objm(nc);
   const os = await objm.create("test", { storage: StorageType.Memory });
-  const sc = StringCodec();
-  await os.put({ name: "blob.txt" }, readableStreamFrom(sc.encode("A")));
-  await os.put({ name: "foo bar" }, readableStreamFrom(sc.encode("A")));
-  await os.put({ name: " " }, readableStreamFrom(sc.encode("A")));
-  await os.put({ name: "*" }, readableStreamFrom(sc.encode("A")));
-  await os.put({ name: ">" }, readableStreamFrom(sc.encode("A")));
+  await os.put(
+    { name: "blob.txt" },
+    readableStreamFrom(new TextEncoder().encode("A")),
+  );
+  await os.put(
+    { name: "foo bar" },
+    readableStreamFrom(new TextEncoder().encode("A")),
+  );
+  await os.put(
+    { name: " " },
+    readableStreamFrom(new TextEncoder().encode("A")),
+  );
+  await os.put(
+    { name: "*" },
+    readableStreamFrom(new TextEncoder().encode("A")),
+  );
+  await os.put(
+    { name: ">" },
+    readableStreamFrom(new TextEncoder().encode("A")),
+  );
   await assertRejects(async () => {
-    await os.put({ name: "" }, readableStreamFrom(sc.encode("A")));
+    await os.put(
+      { name: "" },
+      readableStreamFrom(new TextEncoder().encode("A")),
+    );
   });
   await cleanup(ns, nc);
 });
@@ -342,9 +355,11 @@ Deno.test("objectstore - metadata", async () => {
   }
   const objm = new Objm(nc);
   const os = await objm.create("test", { storage: StorageType.Memory });
-  const sc = StringCodec();
 
-  await os.put({ name: "a" }, readableStreamFrom(sc.encode("A")));
+  await os.put(
+    { name: "a" },
+    readableStreamFrom(new TextEncoder().encode("A")),
+  );
 
   // rename a
   let meta = { name: "b" } as ObjectStoreMeta;
@@ -481,18 +496,20 @@ Deno.test("objectstore - watch initially empty", async () => {
   const infos = await os.list();
   assertEquals(infos.length, 0);
 
-  const sc = StringCodec();
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a")),
+    readableStreamFrom(new TextEncoder().encode("a")),
   );
 
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("aa")),
+    readableStreamFrom(new TextEncoder().encode("aa")),
   );
 
-  await os.put({ name: "b" }, readableStreamFrom(sc.encode("b")));
+  await os.put(
+    { name: "b" },
+    readableStreamFrom(new TextEncoder().encode("b")),
+  );
 
   await done;
 
@@ -515,15 +532,14 @@ Deno.test("objectstore - watch skip history", async () => {
   const objm = new Objm(nc);
   const os = await objm.create("test");
 
-  const sc = StringCodec();
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a")),
+    readableStreamFrom(new TextEncoder().encode("a")),
   );
 
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("aa")),
+    readableStreamFrom(new TextEncoder().encode("aa")),
   );
 
   const buf: ObjectInfo[] = [];
@@ -541,7 +557,10 @@ Deno.test("objectstore - watch skip history", async () => {
     }
   })();
 
-  await os.put({ name: "c" }, readableStreamFrom(sc.encode("c")));
+  await os.put(
+    { name: "c" },
+    readableStreamFrom(new TextEncoder().encode("c")),
+  );
 
   await done;
 
@@ -560,15 +579,14 @@ Deno.test("objectstore - watch history", async () => {
   const objm = new Objm(nc);
   const os = await objm.create("test");
 
-  const sc = StringCodec();
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a")),
+    readableStreamFrom(new TextEncoder().encode("a")),
   );
 
   await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("aa")),
+    readableStreamFrom(new TextEncoder().encode("aa")),
   );
 
   const buf: ObjectInfo[] = [];
@@ -586,7 +604,10 @@ Deno.test("objectstore - watch history", async () => {
     }
   })();
 
-  await os.put({ name: "c" }, readableStreamFrom(sc.encode("c")));
+  await os.put(
+    { name: "c" },
+    readableStreamFrom(new TextEncoder().encode("c")),
+  );
 
   await done;
 
@@ -607,10 +628,9 @@ Deno.test("objectstore - same store link", async () => {
   const objm = new Objm(nc);
   const os = await objm.create("test");
 
-  const sc = StringCodec();
   const src = await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a")),
+    readableStreamFrom(new TextEncoder().encode("a")),
   );
   const oi = await os.link("ref", src);
   assertEquals(oi.options?.link?.bucket, src.bucket);
@@ -635,10 +655,9 @@ Deno.test("objectstore - link of link rejected", async () => {
   const objm = new Objm(nc);
   const os = await objm.create("test");
 
-  const sc = StringCodec();
   const src = await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a")),
+    readableStreamFrom(new TextEncoder().encode("a")),
   );
   const link = await os.link("ref", src);
 
@@ -661,10 +680,9 @@ Deno.test("objectstore - external link", async () => {
   const objm = new Objm(nc);
   const os = await objm.create("test");
 
-  const sc = StringCodec();
   const src = await os.put(
     { name: "a" },
-    readableStreamFrom(sc.encode("a")),
+    readableStreamFrom(new TextEncoder().encode("a")),
   );
 
   const os2 = await objm.create("another");
@@ -793,9 +811,8 @@ Deno.test("objectstore - partials", async () => {
   }
   const objm = new Objm(nc);
   const os = await objm.create("test");
-  const sc = StringCodec();
 
-  const data = sc.encode("".padStart(7, "a"));
+  const data = new TextEncoder().encode("".padStart(7, "a"));
 
   const info = await os.put(
     { name: "test", options: { max_chunk_size: 2 } },
@@ -989,7 +1006,6 @@ Deno.test("objectstore - cannot put links", async () => {
   if (await notCompatible(ns, nc, "2.6.3")) {
     return;
   }
-  const sc = StringCodec();
   const objm = new Objm(nc);
   const os = await objm.create("test");
 
@@ -1001,7 +1017,7 @@ Deno.test("objectstore - cannot put links", async () => {
 
   await assertRejects(
     async () => {
-      await os.put(mm, readableStreamFrom(sc.encode("a")));
+      await os.put(mm, readableStreamFrom(new TextEncoder().encode("a")));
     },
     Error,
     "link cannot be set when putting the object in bucket",
diff --git a/services/deno.json b/services/deno.json
index 2c1e3ca7..ee58151d 100644
--- a/services/deno.json
+++ b/services/deno.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/services",
-  "version": "3.0.0-8",
+  "version": "3.0.0-9",
   "exports": {
     ".": "./src/mod.ts",
     "./internal": "./src/internal_mod.ts"
@@ -33,6 +33,6 @@
     "test": "deno test -A --parallel --reload --quiet tests/ --import-map=import_map.json"
   },
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29"
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30"
   }
 }
diff --git a/services/import_map.json b/services/import_map.json
index 26fb5eff..0c5e9ca1 100644
--- a/services/import_map.json
+++ b/services/import_map.json
@@ -1,7 +1,7 @@
 {
   "imports": {
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
-    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-29/internal",
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
+    "@nats-io/nats-core/internal": "jsr:@nats-io/nats-core@~3.0.0-30/internal",
     "test_helpers": "../test_helpers/mod.ts",
     "@nats-io/nkeys": "jsr:@nats-io/nkeys@1.2.0-4",
     "@nats-io/nuid": "jsr:@nats-io/nuid@2.0.1-2",
diff --git a/services/package.json b/services/package.json
index 20a5f2b9..d27e0f39 100644
--- a/services/package.json
+++ b/services/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/services",
-  "version": "3.0.0-8",
+  "version": "3.0.0-9",
   "files": [
     "lib/",
     "LICENSE",
@@ -34,7 +34,7 @@
   },
   "description": "services library - this library implements all the base functionality for NATS services for javascript clients",
   "dependencies": {
-    "@nats-io/nats-core": "~3.0.0-29"
+    "@nats-io/nats-core": "~3.0.0-30"
   },
   "devDependencies": {
     "@types/node": "^22.7.6",
diff --git a/services/src/service.ts b/services/src/service.ts
index 2071b5d7..fb6036e3 100644
--- a/services/src/service.ts
+++ b/services/src/service.ts
@@ -16,7 +16,6 @@ import {
   deferred,
   Empty,
   headers,
-  JSONCodec,
   nanos,
   nuid,
   parseSemVer,
@@ -130,7 +129,7 @@ export class ServiceMsgImpl implements ServiceMsg {
   respondError(
     code: number,
     description: string,
-    data?: Uint8Array,
+    data?: Payload,
     opts?: PublishOptions,
   ): boolean {
     opts = opts || {};
@@ -488,14 +487,13 @@ export class ServiceImpl implements Service {
   }
 
   start(): Promise<Service> {
-    const jc = JSONCodec();
     const statsHandler = (err: Error | null, msg: Msg): Promise<void> => {
       if (err) {
         this.close(err);
         return Promise.reject(err);
       }
       return this.stats().then((s) => {
-        msg?.respond(jc.encode(s));
+        msg?.respond(JSON.stringify(s));
         return Promise.resolve();
       });
     };
@@ -505,11 +503,11 @@ export class ServiceImpl implements Service {
         this.close(err);
         return Promise.reject(err);
       }
-      msg?.respond(jc.encode(this.info()));
+      msg?.respond(JSON.stringify(this.info()));
       return Promise.resolve();
     };
 
-    const ping = jc.encode(this.ping());
+    const ping = JSON.stringify(this.ping());
     const pingHandler = (err: Error | null, msg: Msg): Promise<void> => {
       if (err) {
         this.close(err).then().catch();
diff --git a/services/src/serviceclient.ts b/services/src/serviceclient.ts
index b6def53e..92493102 100644
--- a/services/src/serviceclient.ts
+++ b/services/src/serviceclient.ts
@@ -14,7 +14,6 @@
  */
 import {
   Empty,
-  JSONCodec,
   QueuedIteratorImpl,
   RequestStrategy,
 } from "@nats-io/nats-core/internal";
@@ -79,13 +78,12 @@ export class ServiceClientImpl implements ServiceClient {
     id = "",
   ): Promise<QueuedIterator<T>> {
     const iter = new QueuedIteratorImpl<T>();
-    const jc = JSONCodec<T>();
     const subj = ServiceImpl.controlSubject(v, name, id, this.prefix);
     const responses = await this.nc.requestMany(subj, Empty, this.opts);
     (async () => {
       for await (const m of responses) {
         try {
-          const s = jc.decode(m.data);
+          const s = m.json<T>();
           iter.push(s);
         } catch (err) {
           // @ts-ignore: pushing fn
diff --git a/services/src/types.ts b/services/src/types.ts
index b105381c..c3c777d3 100644
--- a/services/src/types.ts
+++ b/services/src/types.ts
@@ -2,6 +2,7 @@ import type {
   Msg,
   Nanos,
   NatsError,
+  Payload,
   PublishOptions,
   QueuedIterator,
 } from "@nats-io/nats-core";
@@ -10,7 +11,7 @@ export interface ServiceMsg extends Msg {
   respondError(
     code: number,
     description: string,
-    data?: Uint8Array,
+    data?: Payload,
     opts?: PublishOptions,
   ): boolean;
 }
diff --git a/services/tests/service-check.ts b/services/tests/service-check.ts
index 373b761b..8933a872 100644
--- a/services/tests/service-check.ts
+++ b/services/tests/service-check.ts
@@ -15,7 +15,7 @@
 
 import { cli } from "https://deno.land/x/cobra@v0.0.9/mod.ts";
 import { connect } from "jsr:@nats-io/nats-transport-deno@3.0.0-4";
-import { collect, parseSemVer, StringCodec } from "@nats-io/nats-core/internal";
+import { collect, parseSemVer } from "@nats-io/nats-core/internal";
 
 import type { NatsConnection } from "@nats-io/nats-core/internal";
 
@@ -43,10 +43,10 @@ const root = cli({
     let nc: NatsConnection | null = null;
     try {
       nc = await connect({ servers });
-      await invoke(nc, name);
-      await checkPing(nc, name);
-      await checkInfo(nc, name);
-      await checkStats(nc, name);
+      await invoke(nc!, name);
+      await checkPing(nc!, name);
+      await checkInfo(nc!, name);
+      await checkStats(nc!, name);
     } catch (err) {
       cmd.stderr(err.message);
       console.log(err);
@@ -154,7 +154,7 @@ async function invoke(nc: NatsConnection, name: string): Promise<void> {
 
   // the service should throw/register an error if "error" is specified as payload
   proms = infos.map((v) => {
-    return nc.request(v.endpoints[0].subject, StringCodec().encode("error"));
+    return nc.request(v.endpoints[0].subject, "error");
   });
   responses = await Promise.all(proms);
   responses.forEach((m) => {
@@ -168,14 +168,14 @@ async function invoke(nc: NatsConnection, name: string): Promise<void> {
   proms = infos.map((v, idx) => {
     return nc.request(
       v.endpoints[0].subject,
-      StringCodec().encode(`hello ${idx}`),
+      `hello ${idx}`,
     );
   });
   responses = await Promise.all(proms);
   responses.forEach((m, idx) => {
     const r = `hello ${idx}`;
     assertEquals(
-      StringCodec().decode(m.data),
+      m.string(),
       r,
       `expected service response ${r}`,
     );
diff --git a/services/tests/service_test.ts b/services/tests/service_test.ts
index 61570c20..6b490a1a 100644
--- a/services/tests/service_test.ts
+++ b/services/tests/service_test.ts
@@ -29,9 +29,7 @@ import {
   createInbox,
   delay,
   ErrorCode,
-  JSONCodec,
   nuid,
-  StringCodec,
 } from "@nats-io/nats-core/internal";
 import type {
   Msg,
@@ -102,7 +100,6 @@ Deno.test("service - bad name", async () => {
 
 Deno.test("service - client", async () => {
   const { ns, nc } = await _setup(connect, {}, {});
-  const sc = StringCodec();
   const subj = createInbox();
   const svc = new Svc(nc);
 
@@ -113,7 +110,7 @@ Deno.test("service - client", async () => {
   }) as ServiceImpl;
   srv.addEndpoint("hello", {
     handler: (_err, msg) => {
-      msg?.respond(sc.encode("hello"));
+      msg?.respond("hello");
     },
     subject: subj,
   });
@@ -687,9 +684,9 @@ Deno.test("service - cross platform service test", async () => {
     subject: createInbox(),
     handler: (_err, m): void => {
       if (m.data.length === 0) {
-        m.respondError(400, "need a string", JSONCodec().encode(""));
+        m.respondError(400, "need a string", JSON.stringify(""));
       } else {
-        if (StringCodec().decode(m.data) === "error") {
+        if (m.string() === "error") {
           throw new Error("service asked to throw an error");
         }
         m.respond(m.data);
@@ -723,9 +720,9 @@ Deno.test("service - cross platform service test", async () => {
   const { success, stderr, stdout } = await cmd.output();
 
   if (!success) {
-    console.log(StringCodec().decode(stdout));
-    console.log(StringCodec().decode(stderr));
-    fail(StringCodec().decode(stderr));
+    console.log(new TextDecoder().decode(stdout));
+    console.log(new TextDecoder().decode(stderr));
+    fail(new TextDecoder().decode(stderr));
   }
 
   await nc.close();
@@ -746,7 +743,7 @@ Deno.test("service - stats name respects assigned name", async () => {
   const stats = await test.stats();
   assertEquals(stats.name, "tEsT");
   const r = await nc.request(`$SRV.PING.tEsT`);
-  const si = JSONCodec<ServiceIdentity>().decode(r.data);
+  const si = r.json<ServiceIdentity>();
   assertEquals(si.name, "tEsT");
 
   await cleanup(ns, nc);
@@ -760,21 +757,20 @@ Deno.test("service - multiple endpoints", async () => {
     name: "multi",
     version: "0.0.1",
   });
-  const sc = StringCodec();
   ms.addEndpoint("hey", (_err, m) => {
-    m.respond(sc.encode("hi"));
+    m.respond("hi");
   });
   ms.addGroup("service").addEndpoint("echo", (_err, m) => {
     m.respond(m.data);
   });
 
   let r = await nc.request(`hey`);
-  assertEquals(sc.decode(r.data), "hi");
-  r = await nc.request(`service.echo`, sc.encode("yo!"));
-  assertEquals(sc.decode(r.data), "yo!");
+  assertEquals(r.string(), "hi");
+  r = await nc.request(`service.echo`, "yo!");
+  assertEquals(r.string(), "yo!");
 
   r = await nc.request(`$SRV.STATS`);
-  const stats = JSONCodec().decode(r.data) as ServiceStats;
+  const stats = r.json<ServiceStats>();
 
   function t(name: string) {
     const v = stats.endpoints?.find((n) => {
@@ -945,7 +941,7 @@ Deno.test("service - json reviver", async () => {
     },
   });
 
-  await nc.request("group.endpoint", JSONCodec().encode({ date: Date.now() }));
+  await nc.request("group.endpoint", JSON.stringify({ date: Date.now() }));
 
   await cleanup(ns, nc);
 });
diff --git a/transport-deno/deno.json b/transport-deno/deno.json
index 915b5108..b7aaef40 100644
--- a/transport-deno/deno.json
+++ b/transport-deno/deno.json
@@ -20,7 +20,7 @@
   },
   "imports": {
     "@std/io": "jsr:@std/io@0.224.0",
-    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-29",
+    "@nats-io/nats-core": "jsr:@nats-io/nats-core@~3.0.0-30",
     "@nats-io/nkeys": "jsr:@nats-io/nkeys@1.2.0-4",
     "@nats-io/nuid": "jsr:@nats-io/nuid@2.0.1-2"
   }
diff --git a/transport-node/package-lock.json b/transport-node/package-lock.json
index 160d3e9b..68736119 100644
--- a/transport-node/package-lock.json
+++ b/transport-node/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@nats-io/transport-node",
-  "version": "3.0.0-14",
+  "version": "3.0.0-15",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@nats-io/transport-node",
-      "version": "3.0.0-14",
+      "version": "3.0.0-15",
       "license": "Apache-2.0",
       "dependencies": {
         "@nats-io/nats-core": "~3.0.0-20",
diff --git a/transport-node/package.json b/transport-node/package.json
index 68da683c..8bb3a98e 100644
--- a/transport-node/package.json
+++ b/transport-node/package.json
@@ -1,6 +1,6 @@
 {
   "name": "@nats-io/transport-node",
-  "version": "3.0.0-14",
+  "version": "3.0.0-15",
   "description": "Node.js client for NATS, a lightweight, high-performance cloud native messaging system",
   "keywords": [
     "nats",
@@ -54,7 +54,7 @@
     "node": ">= 18.0.0"
   },
   "dependencies": {
-    "@nats-io/nats-core": "~3.0.0-29",
+    "@nats-io/nats-core": "~3.0.0-30",
     "@nats-io/nkeys": "~1.2.0-7",
     "@nats-io/nuid": "^2.0.1-2"
   },
diff --git a/transport-node/src/version.ts b/transport-node/src/version.ts
index 0bf8b446..7e38d46f 100644
--- a/transport-node/src/version.ts
+++ b/transport-node/src/version.ts
@@ -1,2 +1,2 @@
 // This file is generated - do not edit
-export const version = "3.0.0-14";
+export const version = "3.0.0-15";