diff --git a/.eslintrc.js b/.eslintrc.js
deleted file mode 100644
index 42ddb9f0e..000000000
--- a/.eslintrc.js
+++ /dev/null
@@ -1,53 +0,0 @@
-"use strict";
-
-module.exports = {
-  "env": {
-    "browser": true,
-    "es2021": true,
-  },
-  "extends": ["google"],
-  "overrides": [{
-    // eslint-plugin-html handles eol-last slightly different - it applies to
-    // each set of script tags, so we turn it off here.
-    "files": "**/*.*php",
-    "rules": {
-      "eol-last": "off",
-      "indent": "off",
-    },
-  }],
-  "plugins": [
-    "html",
-    "php-markup",
-  ],
-  "rules": {
-    "no-invalid-this": "off",
-    "camelcase": "off",
-    "comma-dangle": "off",
-    "guard-for-in": "off",
-    "operator-linebreak": "off",
-    "max-len": "off",
-    "new-cap": ["error", {
-      capIsNewExceptions: ["Error", "Warning", "Debug", "Polygon_calcArea", "Play", "Stop", "Panzoom"],
-      newIsCapExceptionPattern: "^Asset\.."
-    }],
-    "no-array-constructor": "off",
-    "no-unused-vars": ["error", {
-      "vars": "local",
-      "args": "none",
-      "ignoreRestSiblings": false
-    }],
-    "no-var": "off",
-    "prefer-rest-params": "off",
-    "quotes": "off",
-    "require-jsdoc": "off",
-    "spaced-comment": "off",
-  },
-  "settings": {
-    "php/php-extensions": [".php"],
-    "php/markup-replacement": {"php": "", "=": "0"},
-    "php/keep-eol": false,
-    "php/remove-whitespace": false,
-    "php/remove-empty-line": false,
-    "php/remove-php-lint": false
-  }
-};
diff --git a/.github/workflows/ci-eslint.yml b/.github/workflows/ci-eslint.yml
index 3bdf8f471..2ad64e3e5 100644
--- a/.github/workflows/ci-eslint.yml
+++ b/.github/workflows/ci-eslint.yml
@@ -19,6 +19,6 @@ jobs:
         with:
           submodules: recursive
       - name: Install ESLint
-        run: npm install eslint@8.7.0 eslint-config-google@0.14.0 eslint-plugin-html@6.2.0 eslint-plugin-php-markup@6.0.0
+        run: npm install eslint@9 @eslint/eslintrc @eslint/js globals eslint-config-google@0.14.0 eslint-plugin-html eslint-plugin-php-markup@6.0.0
       - name: Run ESLint
         run: npx eslint --ext .js.php,.js .
diff --git a/AGENTS.md b/AGENTS.md
index 6842cd335..eb3bfc3a1 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -183,7 +183,7 @@ npx eslint --ext .js.php,.js .        # Lint all
 npx eslint --fix web/js/              # Auto-fix
 ```
 
-ESLint config: `.eslintrc.js` (Google style guide). Runs in CI via `.github/workflows/ci-eslint.yml`.
+ESLint config: `eslint.config.js` (ESLint 9 flat config, Google style guide). Runs in CI via `.github/workflows/ci-eslint.yml`.
 
 ### PHP/API Testing
 
diff --git a/eslint.config.js b/eslint.config.js
index 076deef6c..e077f3b6d 100644
--- a/eslint.config.js
+++ b/eslint.config.js
@@ -1,8 +1,8 @@
 "use strict";
 
 const {
-    defineConfig,
-    globalIgnores,
+  defineConfig,
+  globalIgnores,
 } = require("eslint/config");
 
 const globals = require("globals");
@@ -11,100 +11,102 @@ const phpMarkup = require("eslint-plugin-php-markup");
 const js = require("@eslint/js");
 
 const {
-    FlatCompat,
+  FlatCompat,
 } = require("@eslint/eslintrc");
 
 const compat = new FlatCompat({
-    baseDirectory: __dirname,
-    recommendedConfig: js.configs.recommended,
-    allConfig: js.configs.all
+  baseDirectory: __dirname,
+  recommendedConfig: js.configs.recommended,
+  allConfig: js.configs.all
 });
 
 module.exports = defineConfig([{
-    languageOptions: {
-        globals: {
-            ...globals.browser,
-        },
+  "languageOptions": {
+    globals: {
+      ...globals.browser,
+    },
+  },
+
+  "extends": compat.extends("google"),
+
+  "plugins": {
+    html,
+    "php-markup": phpMarkup,
+  },
+
+  "rules": {
+    "valid-jsdoc": "off",
+    "no-invalid-this": "off",
+    "camelcase": "off",
+    "comma-dangle": "off",
+    "guard-for-in": "off",
+    "operator-linebreak": "off",
+    "max-len": "off",
+
+    "new-cap": ["error", {
+      capIsNewExceptions: ["Error", "Warning", "Debug", "Polygon_calcArea", "Play", "Stop", "Panzoom"],
+      newIsCapExceptionPattern: "^Asset..",
+    }],
+
+    "no-array-constructor": "off",
+
+    "no-unused-vars": ["error", {
+      "vars": "local",
+      "args": "none",
+      "ignoreRestSiblings": false,
+    }],
+
+    "no-var": "off",
+    "prefer-rest-params": "off",
+    "quotes": "off",
+    "require-jsdoc": "off",
+    "spaced-comment": "off",
+  },
+
+  "settings": {
+    "php/php-extensions": [".php"],
+
+    "php/markup-replacement": {
+      "php": "",
+      "=": "0",
     },
 
-    extends: compat.extends("google"),
-
-    plugins: {
-        html,
-        "php-markup": phpMarkup,
-    },
-
-    "rules": {
-        "no-invalid-this": "off",
-        "camelcase": "off",
-        "comma-dangle": "off",
-        "guard-for-in": "off",
-        "max-len": "off",
-
-        "new-cap": ["error", {
-            capIsNewExceptions: ["Error", "Warning", "Debug", "Polygon_calcArea", "Play", "Stop", "Panzoom"],
-            newIsCapExceptionPattern: "^Asset..",
-        }],
-
-        "no-array-constructor": "off",
-
-        "no-unused-vars": ["error", {
-            "vars": "local",
-            "args": "none",
-            "ignoreRestSiblings": false,
-        }],
-
-        "no-var": "off",
-        "prefer-rest-params": "off",
-        "quotes": "off",
-        "require-jsdoc": "off",
-        "spaced-comment": "off",
-    },
-
-    "settings": {
-        "php/php-extensions": [".php"],
-
-        "php/markup-replacement": {
-            "php": "",
-            "=": "0",
-        },
-
-        "php/keep-eol": false,
-        "php/remove-whitespace": false,
-        "php/remove-empty-line": false,
-        "php/remove-php-lint": false,
-    },
+    "php/keep-eol": false,
+    "php/remove-whitespace": false,
+    "php/remove-empty-line": false,
+    "php/remove-php-lint": false,
+  },
 }, {
-    files: ["**/*.*php"],
+  "files": ["**/*.*php"],
 
-    "rules": {
-        "eol-last": "off",
-        "indent": "off",
-    },
+  "rules": {
+    "eol-last": "off",
+    "indent": "off",
+  },
 }, globalIgnores([
-    "**/*.min.js",
-    "web/api/lib",
-    "web/includes/csrf/",
-    "web/js/videojs.zoomrotate.js",
-    "web/js/video-stream.js",
-    "web/js/video-rtc.js",
-    "web/js/fontfaceobserver.standalone.js",
-    "web/skins/classic/js/bootstrap-4.5.0.js",
-    "web/skins/classic/js/bootstrap.bundle.min.js",
-    "web/skins/classic/js/bootstrap-table-1.23.5",
-    "web/skins/classic/js/chosen",
-    "web/skins/classic/js/dateTimePicker",
-    "web/skins/classic/js/jquery-*.js",
-    "web/skins/classic/js/jquery-ui-*",
-    "web/skins/classic/js/jquery.js",
-    "web/skins/classic/js/moment.js",
-    "web/skins/classic/js/video.js",
-    "web/skins/classic/assets",
-    "web/js/janus.js",
-    "web/js/ajaxQueue.js",
-    "web/js/hls-1.5.20/",
-    "web/js/noUiSlider-15.8.1/",
-    "web/js/dms.js",
-    "web/skins/classic/includes/export_functions.php",
-    "web/skins/classic/views/events.php",
+  "**/*.min.js",
+  "web/api/lib",
+  "web/includes/csrf/",
+  "web/js/videojs.zoomrotate.js",
+  "web/js/video-stream.js",
+  "web/js/video-rtc.js",
+  "web/js/fontfaceobserver.standalone.js",
+  "web/skins/classic/js/bootstrap-4.5.0.js",
+  "web/skins/classic/js/bootstrap.bundle.min.js",
+  "web/skins/classic/js/bootstrap-table-1.23.5",
+  "web/skins/classic/js/chosen",
+  "web/skins/classic/js/dateTimePicker",
+  "web/skins/classic/js/jquery-*.js",
+  "web/skins/classic/js/jquery-ui-*",
+  "web/skins/classic/js/jquery.js",
+  "web/skins/classic/js/moment.js",
+  "web/skins/classic/js/video.js",
+  "web/skins/classic/assets",
+  "web/js/janus.js",
+  "web/js/ajaxQueue.js",
+  "web/js/hls-1.6.13/",
+  "web/js/noUiSlider-15.8.1/",
+  "web/js/dms.js",
+  "web/skins/classic/includes/export_functions.php",
+  "web/skins/classic/views/events.php",
 ])]);