manifest.json File Format

Introduction

manifest.json is the file every browser extension has at its top level. It is what makes a folder an extension: its name and version, the permissions it asks for, and the scripts and pages it uses. It is used by Chrome and the other Chromium browsers, and by Firefox and Safari, which follow the same WebExtensions design. In a package it sits at the top of a .crx or .xpi file.

The file is JSON, and MDN notes it may also contain // comments. A file dropped on any page of this site, and named manifest.json with a manifest_version, opens in the explorer with its permissions and keys explained.

Structure

The file holds one JSON object. Only three keys are required on every browser.

{
  "manifest_version": 3,
  "name": "Sample Extension",
  "version": "1.0",
  "description": "A sample",
  "icons": { "128": "icon.png" },
  "action": { "default_popup": "popup.html" },
  "background": { "service_worker": "worker.js" },
  "permissions": ["storage"],
  "host_permissions": ["https://*.example.org/*"]
}

The rest of the format is described on these pages:

• Keys – every key, and the structure of the main ones
• Permissions – what each permission allows, and the host permissions

Manifest versions

Chrome supports only Manifest V3 now. Chrome 139 removed Manifest V2, and the remaining Manifest V2 extensions were removed from the Chrome Web Store on 31 August 2026. Firefox supports both.

Also used for

• GeoJSON – Map points, lines and areas with properties, written as JSON.
• Hugging Face model config (config.json) – config.json: a model’s architecture and sizes, read before the weights.
• Hugging Face tokenizer (tokenizer.json) – tokenizer.json: a language model’s vocabulary and tokenising rules.
• JSON Schema – A JSON document that describes and validates other JSON documents.
• JavaScript Object Notation – Text format for objects, arrays, strings, numbers and booleans.
• Lottie animation – Vector animations as JSON, exported from After Effects and played in apps and web pages.
• Visual Studio Code settings – VS Code’s settings.json: dotted setting IDs in JSON with comments.
• npm package manifest (package.json) – A JavaScript package’s name, version, scripts and dependencies, in JSON.

Links