diff --git a/src/main.ts b/src/main.ts
index 2e9c819..6352b53 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -8,6 +8,22 @@ import {scanFiles} from './stages/scan-files.js';
 import {fixFiles} from './stages/fix-files.js';
 import {traverseFiles} from './stages/traverse-files.js';
 import {scanDependencies} from './stages/scan-dependencies.js';
+import {availableParallelism} from 'node:os';
+
+function getWantedThreads(scanSpeed: string): number {
+  const threads = availableParallelism();
+  switch (scanSpeed) {
+    case 'slow':
+      return threads * 0.25;
+    case 'medium':
+      return threads * 0.5;
+    case 'fast':
+      return threads * 0.75;
+    case 'fastest':
+      return threads;
+  }
+  return 1;
+}
 
 const availableManifests: Record<string, modReplacements.ManifestModule> = {
   native: modReplacements.nativeReplacements,
@@ -118,6 +134,38 @@ async function runModuleReplacements(): Promise<void> {
         cl.confirm({
           message: 'Automatically uninstall packages?',
           initialValue: false
+        }),
+      scanSpeed: () =>
+        cl.select({
+          message: 'Preferred scan speed',
+          options: [
+            {
+              value: 'fastest',
+              label: 'Fastest',
+              hint: 'uses all the threads, pushes cpu to 100%'
+            },
+            {
+              value: 'fast',
+              label: 'Fast',
+              hint: '75% of available threads'
+            },
+            {
+              value: 'medium',
+              label: 'Medium',
+              hint: '50% of available threads'
+            },
+            {
+              value: 'slow',
+              label: 'Slow',
+              hint: '25% of available threads'
+            },
+            {
+              value: 'slowest',
+              label: 'Slowest',
+              hint: 'disables parallelism, 1 thread'
+            }
+          ],
+          initialValue: 'fast'
         })
     },
     {
@@ -198,13 +246,15 @@ async function runModuleReplacements(): Promise<void> {
 
   try {
     const files = await traverseFiles(options.filesDir);
-
+    const threads = getWantedThreads(options.scanSpeed);
+    console.time('scan');
     const scanFilesResult = await scanFiles(
       files,
       manifestReplacements,
+      threads,
       scanSpinner
     );
-
+    console.timeEnd('scan');
     if (scanFilesResult.length > 0) {
       dependenciesFound = true;
     }
diff --git a/src/stages/scan-files.ts b/src/stages/scan-files.ts
index f3d2a94..e4ab066 100644
--- a/src/stages/scan-files.ts
+++ b/src/stages/scan-files.ts
@@ -13,6 +13,7 @@ const available = availableParallelism();
 export function scanFiles(
   files: string[],
   replacements: modReplacements.ModuleReplacement[],
+  threads: number,
   spinner: ReturnType<typeof cl.spinner>
 ): Promise<FileReplacement[]> {
   return new Promise((resolve, reject) => {
@@ -21,7 +22,7 @@ export function scanFiles(
     const filesLength = files.length;
     const results: FileReplacement[] = [];
 
-    for (const file of files.splice(0, available)) {
+    for (const file of files.splice(0, threads)) {
       const worker = new Worker(`${__dirname}/workers/scan-file.js`);
       // todo, what todo with the errors?
       worker.on('error', (error) => reject(error.message));
diff --git a/src/stages/workers/scan-file.ts b/src/stages/workers/scan-file.ts
index 013a936..b9670dd 100644
--- a/src/stages/workers/scan-file.ts
+++ b/src/stages/workers/scan-file.ts
@@ -1,11 +1,11 @@
 import * as modReplacements from 'module-replacements';
 import {ts as sg} from '@ast-grep/napi';
-import {readFile} from 'node:fs/promises';
 import dedent from 'dedent';
 import pc from 'picocolors';
 import {type FileReplacement} from './../../shared-types.js';
 import {suggestReplacement} from './../../suggest-replacement.js';
 import {parentPort} from 'node:worker_threads';
+import {open} from 'node:fs/promises';
 
 async function scanFile(
   filePath: string,
@@ -85,9 +85,11 @@ async function scanTask(
   replacements: modReplacements.ModuleReplacement[]
 ) {
   try {
-    const contents = await readFile(file, 'utf8');
+    const fd = await open(file);
+    const contents = await fd.readFile({encoding: 'utf-8'});
     const lines = contents.split('\n');
     const scanResult = await scanFile(file, contents, lines, replacements);
+    await fd.close();
 
     parentPort?.postMessage({type: 'result', value: scanResult});
   } catch (err) {