diff --git a/.changeset/wise-berries-yawn.md b/.changeset/wise-berries-yawn.md
new file mode 100644
index 0000000..c1d6bf7
--- /dev/null
+++ b/.changeset/wise-berries-yawn.md
@@ -0,0 +1,5 @@
+---
+'@ssecd/jkn': minor
+---
+
+add custom base url config
diff --git a/README.md b/README.md
index 74bbd6e..ba2542f 100644
--- a/README.md
+++ b/README.md
@@ -125,13 +125,15 @@ function persistSep(sep: VClaimResponse<'sep', 'insertV2'>) {
 
 Konfigurasi mengikuti interface berikut:
 
-```ts
+````ts
 interface Config {
 	/**
 	 * Kode PPK yang diberikan BPJS.
 	 *
 	 * Diperlukan untuk melakukan proses encryption
 	 * pada web service eRekam Medis.
+	 *
+	 * @default process.env.JKN_PPK_CODE
 	 */
 	ppkCode: string;
 
@@ -214,8 +216,24 @@ interface Config {
 	 * @default false
 	 */
 	throw: boolean;
+
+	/**
+	 * Base URL web service dari BPJS. Secara default sudah diatur
+	 * berdasarkan base url yang ada di TrustMark. Nilai dapat diatur
+	 * secara partial, misalnya:
+	 *
+	 * ```
+	 * baseUrls: {
+	 * 	vclaim: {
+	 * 		development: 'http://dev.example.com',
+	 * 		production: 'http://prod.example.com'
+	 * 	}
+	 * }
+	 * ```
+	 */
+	baseUrls: Partial<Record<Type, Record<Mode, string>>>;
 }
-```
+````
 
 ## API Tersedia
 
diff --git a/src/fetcher.ts b/src/fetcher.ts
index e7eb74f..64ff391 100644
--- a/src/fetcher.ts
+++ b/src/fetcher.ts
@@ -13,6 +13,8 @@ export interface Config {
 	 *
 	 * Diperlukan untuk melakukan proses encryption
 	 * pada web service eRekam Medis.
+	 *
+	 * @default process.env.JKN_PPK_CODE
 	 */
 	ppkCode: string;
 
@@ -95,6 +97,22 @@ export interface Config {
 	 * @default false
 	 */
 	throw: boolean;
+
+	/**
+	 * Base URL web service dari BPJS. Secara default sudah diatur
+	 * berdasarkan base url yang ada di TrustMark. Nilai dapat diatur
+	 * secara partial, misalnya:
+	 *
+	 * ```
+	 * baseUrls: {
+	 * 	vclaim: {
+	 * 		development: 'http://dev.example.com',
+	 * 		production: 'http://prod.example.com'
+	 * 	}
+	 * }
+	 * ```
+	 */
+	baseUrls: Partial<Record<Type, Record<Mode, string>>>;
 }
 
 export interface SendOption {
@@ -140,7 +158,7 @@ export type SendResponse<T> = {
 	rekamMedis: LowerResponse<T, string>;
 };
 
-const api_base_urls: Record<Type, Record<Mode, string>> = {
+const defaultBaseUrls: Record<Type, Record<Mode, string>> = {
 	vclaim: {
 		development: 'https://apijkn-dev.bpjs-kesehatan.go.id/vclaim-rest-dev',
 		production: 'https://apijkn.bpjs-kesehatan.go.id/vclaim-rest'
@@ -181,7 +199,8 @@ export class Fetcher {
 		pcareUserKey: process.env.JKN_PCARE_USER_KEY ?? '',
 		icareUserKey: process.env.JKN_ICARE_USER_KEY ?? '',
 		rekamMedisUserKey: process.env.JKN_REKAM_MEDIS_USER_KEY ?? '',
-		throw: false
+		throw: false,
+		baseUrls: defaultBaseUrls
 	};
 
 	constructor(private userConfig?: Partial<Config> | (() => MaybePromise<Partial<Config>>)) {}
@@ -190,16 +209,10 @@ export class Fetcher {
 		if (!this.userConfig || this.configured) return;
 
 		if (typeof this.userConfig === 'object') {
-			this.config = {
-				...this.config,
-				...this.userConfig
-			};
+			this.config = this.mergeConfig(this.config, this.userConfig);
 		} else if (typeof this.userConfig === 'function') {
-			const config = await this.userConfig();
-			this.config = {
-				...this.config,
-				...config
-			};
+			const userConfig = await this.userConfig();
+			this.config = this.mergeConfig(this.config, userConfig);
 		}
 
 		if (!this.config.consId || !this.config.consSecret) {
@@ -209,6 +222,12 @@ export class Fetcher {
 		this.configured = true;
 	}
 
+	private mergeConfig(target: Config, source: Partial<Config>): Config {
+		// simple object merge strategy because only baseUrls is typeof object for now
+		const baseUrls = { ...target.baseUrls, ...source.baseUrls };
+		return { ...target, ...source, baseUrls };
+	}
+
 	private get userKeyMap(): Record<Type, string | undefined> {
 		return {
 			vclaim: this.config.vclaimUserKey,
@@ -260,7 +279,10 @@ export class Fetcher {
 
 		let response = '';
 		try {
-			const url = new URL(api_base_urls[type][this.config.mode] + option.path);
+			const baseUrl = this.config.baseUrls[type];
+			if (!baseUrl) throw new Error(`base url of type "${type}" is invalid`);
+
+			const url = new URL(baseUrl[this.config.mode] + option.path);
 			const init: RequestInit = { method: option.method ?? 'GET' };
 			const headers = { ...this.getDefaultHeaders(type), ...(option.headers ?? {}) };
 
diff --git a/test/fetcher.test.ts b/test/fetcher.test.ts
new file mode 100644
index 0000000..ef28fef
--- /dev/null
+++ b/test/fetcher.test.ts
@@ -0,0 +1,25 @@
+import { describe, expect, it } from 'vitest';
+import { Fetcher } from '../src/fetcher';
+
+describe('Fetcher', () => {
+	it.concurrent('validate config', async () => {
+		const userConfig = {
+			ppkCode: '12345',
+			baseUrls: {
+				pcare: {
+					development: 'http://dev.example.com',
+					production: 'http://example.com'
+				}
+			}
+		};
+		const fetcher = new Fetcher(userConfig);
+		const config = await fetcher.getConfig();
+
+		expect(config.ppkCode).toBe(userConfig.ppkCode);
+		expect(config.baseUrls.pcare).toEqual(userConfig.baseUrls.pcare);
+		expect(config.baseUrls.pcare?.development).toBe(userConfig.baseUrls.pcare.development);
+		expect(config.baseUrls.vclaim?.development).toBe(
+			'https://apijkn-dev.bpjs-kesehatan.go.id/vclaim-rest-dev'
+		);
+	});
+});