diff --git a/.eslintrc.js b/.eslintrc.js
index 94bf6675d..f02e0a4ed 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 'use strict';
 
 const restrictedGlobals = require('confusing-browser-globals');
@@ -78,6 +86,8 @@ module.exports = {
   plugins: [
     'sort-keys-fix',
     'simple-import-sort',
+    'header',
+
     // import helps to configure simple-import-sort
     'import',
     'jest',
@@ -92,11 +102,13 @@ module.exports = {
   // and then enable some React specific ones.
   rules: {
     'accessor-pairs': OFF,
+
     'brace-style': [ERROR, '1tbs'],
     'consistent-return': OFF,
     'dot-location': [ERROR, 'property'],
     // We use console['error']() as a signal to not transform it:
     'dot-notation': [ERROR, {allowPattern: '^(error|warn)$'}],
+
     'eol-last': ERROR,
     eqeqeq: [ERROR, 'allow-null'],
     // Prettier forces semicolons in a few places
@@ -104,6 +116,8 @@ module.exports = {
 
     'flowtype/sort-keys': ERROR,
 
+    'header/header': [2, 'scripts/www/headerTemplate.js'],
+
     // (This helps configure simple-import-sort) Make sure all imports are at the top of the file
     'import/first': ERROR,
 
diff --git a/babel.config.js b/babel.config.js
index 7b448b8d9..ff972262b 100644
--- a/babel.config.js
+++ b/babel.config.js
@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 'use strict';
 
 module.exports = {
diff --git a/jest.config.js b/jest.config.js
index 143a3f93d..10d16d400 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 'use strict';
 
 const common = {
diff --git a/libdefs/dom.js b/libdefs/dom.js
index 2f1374738..631003d96 100644
--- a/libdefs/dom.js
+++ b/libdefs/dom.js
@@ -1,4 +1,12 @@
-/* eslint-disable strict */
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
+// eslint-disable-next-line strict
 declare type WindowSelection = {
   anchorNode: Node | null,
   anchorOffset: number,
diff --git a/libdefs/environment.js b/libdefs/environment.js
index c1012f71f..37b97342e 100644
--- a/libdefs/environment.js
+++ b/libdefs/environment.js
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 'use strict';
diff --git a/libdefs/prismjs.js b/libdefs/prismjs.js
index 05aaca555..0aca744ec 100644
--- a/libdefs/prismjs.js
+++ b/libdefs/prismjs.js
@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 'use strict';
 
 type TokenStream = Array<string | Token>;
diff --git a/libdefs/react.js b/libdefs/react.js
index cda171b5f..125da28ae 100644
--- a/libdefs/react.js
+++ b/libdefs/react.js
@@ -1,4 +1,13 @@
-/* eslint-disable strict */
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 // Flow comes with a pretty good library definitions for React, and it
 // includes a type for useRef but no definition for the ref object itself.
+
+// eslint-disable-next-line strict
 declare type RefObject<T> = {current: null | T};
diff --git a/libdefs/yjs.js b/libdefs/yjs.js
index e09bd44c7..b58fc7a83 100644
--- a/libdefs/yjs.js
+++ b/libdefs/yjs.js
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 'use strict';
diff --git a/packages/lexical-playground/__tests__/e2e/CharacterLimit.spec.mjs b/packages/lexical-playground/__tests__/e2e/CharacterLimit.spec.mjs
index ad87eadd7..d243012f0 100644
--- a/packages/lexical-playground/__tests__/e2e/CharacterLimit.spec.mjs
+++ b/packages/lexical-playground/__tests__/e2e/CharacterLimit.spec.mjs
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 import {
diff --git a/packages/lexical-playground/__tests__/utils/index.mjs b/packages/lexical-playground/__tests__/utils/index.mjs
index a4bf39ae8..1aabe3a46 100644
--- a/packages/lexical-playground/__tests__/utils/index.mjs
+++ b/packages/lexical-playground/__tests__/utils/index.mjs
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 import {expect, test as base} from '@playwright/test';
diff --git a/packages/lexical-website-new/babel.config.js b/packages/lexical-website-new/babel.config.js
index 468cd8c31..ab18191bf 100644
--- a/packages/lexical-website-new/babel.config.js
+++ b/packages/lexical-website-new/babel.config.js
@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 'use strict';
 
 module.exports = {
diff --git a/packages/lexical-website-new/docusaurus.config.js b/packages/lexical-website-new/docusaurus.config.js
index 90ad8afa9..cbbd50955 100644
--- a/packages/lexical-website-new/docusaurus.config.js
+++ b/packages/lexical-website-new/docusaurus.config.js
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- *
  */
 
 'use strict';
diff --git a/packages/lexical-website-new/plugins/webpack-buffer/index.js b/packages/lexical-website-new/plugins/webpack-buffer/index.js
index 7a0b3b55d..b55366723 100644
--- a/packages/lexical-website-new/plugins/webpack-buffer/index.js
+++ b/packages/lexical-website-new/plugins/webpack-buffer/index.js
@@ -4,8 +4,8 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- *
  */
+
 'use strict';
 
 const webpack = require('webpack');
diff --git a/packages/lexical-website-new/sidebars.js b/packages/lexical-website-new/sidebars.js
index 233f37393..2a736969d 100644
--- a/packages/lexical-website-new/sidebars.js
+++ b/packages/lexical-website-new/sidebars.js
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- *
  */
 
 'use strict';
diff --git a/packages/lexical-website-new/src/components/CommunityLinks/index.js b/packages/lexical-website-new/src/components/CommunityLinks/index.js
index 5fd6561da..529d95010 100644
--- a/packages/lexical-website-new/src/components/CommunityLinks/index.js
+++ b/packages/lexical-website-new/src/components/CommunityLinks/index.js
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- *
  */
 
 import Link from '@docusaurus/Link';
diff --git a/packages/lexical-website-new/src/components/ImageSwitcher/index.js b/packages/lexical-website-new/src/components/ImageSwitcher/index.js
index 93f9b9530..e4d20a867 100644
--- a/packages/lexical-website-new/src/components/ImageSwitcher/index.js
+++ b/packages/lexical-website-new/src/components/ImageSwitcher/index.js
@@ -4,7 +4,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- *
  */
 
 import {useColorMode} from '@docusaurus/theme-common';
diff --git a/playwright.config.js b/playwright.config.js
index a36f71bf0..a12c4a49c 100644
--- a/playwright.config.js
+++ b/playwright.config.js
@@ -1,3 +1,11 @@
+/**
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ *
+ */
+
 'use strict';
 const {devices} = require('@playwright/test');
 
diff --git a/scripts/build.js b/scripts/build.js
index 8c8303502..69a5ae107 100644
--- a/scripts/build.js
+++ b/scripts/build.js
@@ -3,6 +3,7 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
 
 'use strict';
diff --git a/scripts/check-flow-types.js b/scripts/check-flow-types.js
index 5f65ba7ee..b073ad27c 100644
--- a/scripts/check-flow-types.js
+++ b/scripts/check-flow-types.js
@@ -3,6 +3,7 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
 
 'use strict';
diff --git a/scripts/clean.js b/scripts/clean.js
index c53b3dcf5..bc7ef8788 100644
--- a/scripts/clean.js
+++ b/scripts/clean.js
@@ -3,6 +3,7 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
 
 'use strict';
diff --git a/scripts/error-codes/evalToString.js b/scripts/error-codes/evalToString.js
index 442b71bb2..f61ff535e 100644
--- a/scripts/error-codes/evalToString.js
+++ b/scripts/error-codes/evalToString.js
@@ -4,8 +4,8 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
  */
+
 'use strict';
 
 function evalToString(ast /* : Object */) /* : string */ {
diff --git a/scripts/error-codes/extract-errors.js b/scripts/error-codes/extract-errors.js
index 611c1b0e7..fc12e8c97 100644
--- a/scripts/error-codes/extract-errors.js
+++ b/scripts/error-codes/extract-errors.js
@@ -3,7 +3,9 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
+
 'use strict';
 
 const parser = require('@babel/parser');
diff --git a/scripts/error-codes/formatProdErrorMessage.js b/scripts/error-codes/formatProdErrorMessage.js
index ccbf4d6db..d712749eb 100644
--- a/scripts/error-codes/formatProdErrorMessage.js
+++ b/scripts/error-codes/formatProdErrorMessage.js
@@ -5,6 +5,7 @@
  * LICENSE file in the root directory of this source tree.
  *
  */
+
 'use strict';
 
 // Do not require this module directly! Use normal `invariant` calls with
diff --git a/scripts/error-codes/invertObject.js b/scripts/error-codes/invertObject.js
index 71cb7f3de..1029e6c25 100644
--- a/scripts/error-codes/invertObject.js
+++ b/scripts/error-codes/invertObject.js
@@ -4,8 +4,8 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow
  */
+
 'use strict';
 
 /*:: import type { ErrorMap } from './Types' */
diff --git a/scripts/error-codes/transform-error-messages.js b/scripts/error-codes/transform-error-messages.js
index 34f18e550..6dd338703 100644
--- a/scripts/error-codes/transform-error-messages.js
+++ b/scripts/error-codes/transform-error-messages.js
@@ -3,7 +3,9 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
+
 'use strict';
 
 const fs = require('fs');
diff --git a/scripts/npm/packages.js b/scripts/npm/packages.js
index dfbdc760d..2073e8199 100644
--- a/scripts/npm/packages.js
+++ b/scripts/npm/packages.js
@@ -6,7 +6,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 'use strict';
diff --git a/scripts/npm/prepare-release.js b/scripts/npm/prepare-release.js
index f46dc9499..b7ba66461 100644
--- a/scripts/npm/prepare-release.js
+++ b/scripts/npm/prepare-release.js
@@ -6,7 +6,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 'use strict';
diff --git a/scripts/npm/release.js b/scripts/npm/release.js
index 446d3d17a..03168c450 100644
--- a/scripts/npm/release.js
+++ b/scripts/npm/release.js
@@ -6,7 +6,6 @@
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
  *
- * @flow strict
  */
 
 'use strict';
diff --git a/scripts/updateVersion.js b/scripts/updateVersion.js
index 2880f95bc..2d3f2be2f 100644
--- a/scripts/updateVersion.js
+++ b/scripts/updateVersion.js
@@ -3,6 +3,7 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
 
 'use strict';
diff --git a/scripts/www/rewriteImports.js b/scripts/www/rewriteImports.js
index 39537d31e..68de4e800 100644
--- a/scripts/www/rewriteImports.js
+++ b/scripts/www/rewriteImports.js
@@ -3,6 +3,7 @@
  *
  * This source code is licensed under the MIT license found in the
  * LICENSE file in the root directory of this source tree.
+ *
  */
 
 'use strict';