diff --git a/common/autoinstallers/license-header/index.js b/common/autoinstallers/license-header/index.js
index 22304a9163..8ffab83f59 100644
--- a/common/autoinstallers/license-header/index.js
+++ b/common/autoinstallers/license-header/index.js
@@ -57,6 +57,11 @@ function addLicenseHeader(targetDir, licenseContent, options = {}) {
       .join("\n") +
     (commentSuffix ? "\n" + commentSuffix : "") +
     "\n\n";
+  const licenseHeader = licensedText.trim();
+  const licenseHeaders = [
+    licenseHeader,
+    licenseHeader.replace(/\n/g, "\r\n"),
+  ];
 
   function traverseDir(currentDir) {
     const entries = fs.readdirSync(currentDir, { withFileTypes: true });
@@ -88,7 +93,14 @@ function addLicenseHeader(targetDir, licenseContent, options = {}) {
       const originalContent = fs.readFileSync(filePath, "utf8");
 
       // Check if the license already exists (simple match at the beginning)
-      if (!force && (originalContent.startsWith(licensedText.trim()) || bashHeaders.some(_header => originalContent.startsWith(_header.trim())) || originalContent.startsWith(rushPreHeader.trim()))) {
+      if (
+        !force &&
+        (licenseHeaders.some(_header => originalContent.startsWith(_header)) ||
+          bashHeaders.some(_header =>
+            originalContent.startsWith(_header.trim()),
+          ) ||
+          originalContent.startsWith(rushPreHeader.trim()))
+      ) {
         return;
       }
 
diff --git a/common/autoinstallers/license-header/index.test.js b/common/autoinstallers/license-header/index.test.js
new file mode 100644
index 0000000000..511d74f3a7
--- /dev/null
+++ b/common/autoinstallers/license-header/index.test.js
@@ -0,0 +1,123 @@
+/**
+ * Copyright (c) 2025 Bytedance Ltd. and/or its affiliates
+ * SPDX-License-Identifier: MIT
+ */
+
+const assert = require("node:assert/strict");
+const { execFileSync } = require("node:child_process");
+const fs = require("node:fs");
+const os = require("node:os");
+const path = require("node:path");
+const { afterEach, test } = require("node:test");
+
+const canonicalHeader = `/**
+ * Copyright (c) 2025 Bytedance Ltd. and/or its affiliates
+ * SPDX-License-Identifier: MIT
+ */`;
+const temporaryDirectories = [];
+
+afterEach(() => {
+  for (const directory of temporaryDirectories.splice(0)) {
+    fs.rmSync(directory, { recursive: true, force: true });
+  }
+});
+
+function createFixtureRepository(files) {
+  const root = fs.mkdtempSync(
+    path.join(os.tmpdir(), "flowgram-license-header-")
+  );
+  temporaryDirectories.push(root);
+
+  const scriptDirectory = path.join(
+    root,
+    "common",
+    "autoinstallers",
+    "license-header"
+  );
+  fs.mkdirSync(scriptDirectory, { recursive: true });
+  fs.copyFileSync(
+    __filename.replace(/\.test\.js$/, ".js"),
+    path.join(scriptDirectory, "index.js")
+  );
+  fs.writeFileSync(path.join(root, ".gitignore"), "node_modules\n");
+
+  for (const [relativePath, content] of Object.entries(files)) {
+    const filePath = path.join(root, relativePath);
+    fs.mkdirSync(path.dirname(filePath), { recursive: true });
+    fs.writeFileSync(filePath, content);
+  }
+
+  return { root, scriptDirectory };
+}
+
+function runLicenseHeaderScript(scriptDirectory) {
+  const nodeModulesDirectory = path.dirname(
+    path.dirname(require.resolve("ignore/package.json"))
+  );
+
+  return execFileSync(process.execPath, ["index.js"], {
+    cwd: scriptDirectory,
+    encoding: "utf8",
+    env: {
+      ...process.env,
+      NODE_PATH: nodeModulesDirectory,
+    },
+  });
+}
+
+test("leaves canonical LF and CRLF headers byte-identical", () => {
+  const lfContent = `${canonicalHeader}\n\nconst lf = true;\n`;
+  const crlfContent = lfContent.replace(/\n/g, "\r\n");
+  const { root, scriptDirectory } = createFixtureRepository({
+    "fixtures/lf.ts": lfContent,
+    "fixtures/crlf.ts": crlfContent,
+  });
+
+  runLicenseHeaderScript(scriptDirectory);
+
+  assert.equal(
+    fs.readFileSync(path.join(root, "fixtures/lf.ts"), "utf8"),
+    lfContent
+  );
+  assert.equal(
+    fs.readFileSync(path.join(root, "fixtures/crlf.ts"), "utf8"),
+    crlfContent
+  );
+});
+
+test("adds one canonical header to an unlicensed file and stays idempotent", () => {
+  const source = "const value = 1;\n";
+  const { root, scriptDirectory } = createFixtureRepository({
+    "fixtures/missing.ts": source,
+  });
+
+  runLicenseHeaderScript(scriptDirectory);
+  const firstRun = fs.readFileSync(
+    path.join(root, "fixtures/missing.ts"),
+    "utf8"
+  );
+  runLicenseHeaderScript(scriptDirectory);
+  const secondRun = fs.readFileSync(
+    path.join(root, "fixtures/missing.ts"),
+    "utf8"
+  );
+
+  assert.equal(firstRun, `${canonicalHeader}\n\n${source}`);
+  assert.equal(secondRun, firstRun);
+});
+
+test("leaves a recognized shebang byte-identical", () => {
+  const source = '#!/usr/bin/env node\r\nconsole.log("ok");\r\n';
+  const { root, scriptDirectory } = createFixtureRepository({
+    "fixtures/command.js": source,
+  });
+
+  runLicenseHeaderScript(scriptDirectory);
+  runLicenseHeaderScript(scriptDirectory);
+
+  const result = fs.readFileSync(
+    path.join(root, "fixtures/command.js"),
+    "utf8"
+  );
+  assert.equal(result, source);
+});
diff --git a/common/autoinstallers/license-header/package.json b/common/autoinstallers/license-header/package.json
index f28241f7c3..30c5362191 100644
--- a/common/autoinstallers/license-header/package.json
+++ b/common/autoinstallers/license-header/package.json
@@ -4,7 +4,8 @@
   "private": true,
   "author": "289056872@qq.com",
   "scripts": {
-    "license-header-fix": "node ./index.js"
+    "license-header-fix": "node ./index.js",
+    "test": "node --test index.test.js"
   },
   "dependencies": {
     "ignore": "^7.0.4"