What is manifest.json in a Chrome extension?

It is the single required file at the root of every Chrome extension: a JSON document that tells the browser what the extension is called, what version it is, and what it is allowed to do. Chrome reads it at install time to build the permission consent dialog, wire up your popup, background service worker, and content scripts, and decide which APIs your code may call. If manifest.json is missing or malformed, the extension will not load at all — chrome://extensions reports the parse error and stops.

What does a minimal valid Manifest V3 manifest.json look like?

Only three fields are strictly required: {"manifest_version": 3, "name": "My Extension", "version": "1.0"}. That already loads in chrome://extensions. In practice you also want description and icons (the Web Store listing uses both), and then one key per capability — action for a toolbar popup, background.service_worker for event handling, content_scripts to inject code into pages, and permissions/host_permissions for API and site access. This generator starts from that minimal core and only adds keys for features you actually toggle on.

How accurate is the install-warning preview?

It reproduces the aggregated consent dialog Chrome shows at install time. Each permission that warns on its own (like history, geolocation, or proxy) maps to Chrome's own wording, host match patterns become "Read and change your data on ", and a broad pattern such as or https://*/* collapses to "on all websites". Overlapping warnings are deduped and the stronger one wins — for example history's warning subsumes the weaker "Read your browsing history" from tabs.

Does it support both Manifest V3 and V2?

Yes. Switching version rewrites the keys correctly: V3 uses action, service_worker background, and separate host_permissions, while V2 uses browser_action, background scripts, and folds host patterns into permissions. The permission picker also hides version-specific entries — scripting and sidePanel are V3-only; webRequestBlocking is V2-only. The validator flags V2 as no longer accepted in the Web Store and disabled in Chrome 139+.

What's inside the downloaded starter project?

The ZIP contains a manifest.json plus a stub file for every feature you enabled: a service worker or background page, popup.html/popup.js for the action, the JS/CSS files named in your content scripts, options.html/options.js, sidepanel.html, DevTools pages, new-tab/history/bookmarks override pages, and an icons README. It is a loadable unpacked extension — unzip it and load the folder via "Load unpacked" in chrome://extensions.

What does the validation check for?

It separates store-blocking errors from best-practice warnings. Errors include a missing name or version, a malformed version string, a side panel without the sidePanel permission, and webRequestBlocking under V3. Warnings cover names over 75 characters, descriptions over 132, script injection without host access or activeTab, suspicious keyboard-shortcut syntax, and MV3 web-accessible resources missing a matches list.

How do I add host access and content scripts?

Enter host match patterns in the Host permissions box, one per line — for example https://*.example.com/* or . These drive the install-warning preview. Add content scripts with the Add button, then set match patterns, JS and CSS file names, a run_at timing (document_idle, document_start, or document_end), and the all-frames flag. The generator de-duplicates and shapes everything into a valid content_scripts array.

Will the generated extension work in Firefox and Edge?

Edge runs Chromium manifests unchanged, so you can publish the same package to the Edge Add-ons store. For Firefox the Advanced section lists practical notes — add browser_specific_settings.gecko.id, supply background.scripts alongside service_worker for MV3, and use sidebar_action instead of side_panel. The notes update based on which features your manifest uses.

Chrome Extension Manifest Generator

Build a complete, valid manifest.json for Chrome/Edge extensions (Manifest V3 or V2) with a searchable permission picker, a live install-warning preview that mirrors Chrome's consent dialog, validation, and a one-click runnable starter-project ZIP.

About this ToolHow it works, benefits & use cases

Hand-writing a manifest.json means memorising which keys belong to Manifest V3, which permissions trip Chrome's install dialog, and which fields the Web Store silently truncates. This generator turns all of that into a form. Toggle features — toolbar popup, background service worker, side panel, DevTools page, new-tab override, options page, omnibox keyword — and the manifest rebuilds live in the output panel. A searchable permission picker groups every Chrome permission by area, color-codes each by risk, and feeds an install-warning preview that reproduces the exact consent dialog users see: host patterns collapse to "Read and change your data on…", broad access becomes "…on all websites", and overlapping warnings are deduped like the real thing. Inline validation flags Web-Store blockers and best-practice issues, and when the manifest is clean you can download a runnable unpacked extension — manifest plus stub popup, service worker, content scripts, options, and icon notes — as a ZIP.

How to Use

1Pick Manifest V3 (the current standard) or V2, or click a starter template such as Popup action, Content script, Side panel, New tab page, DevTools panel, or Context menu.
2Fill in Basics (name, version, description) and flip on the Features you need — the manifest.json panel updates as you type.
3Search and toggle permissions in the picker, then list host match patterns one per line; watch the Install permission preview show exactly what Chrome will warn users about.
4Add content scripts, keyboard shortcuts, and web-accessible resources with the Add buttons, and open Advanced & metadata for short name, CSP, incognito mode, and cross-browser notes.
5Check the Validation card — fix any red errors, review amber warnings — then copy the JSON or click "Download starter project" to get a runnable ZIP.

Key Benefits

Live manifest.json output that rebuilds as you toggle features and permissions
Install-warning preview mirrors Chrome's real consent dialog, including host-pattern phrasing and warning dedupe
Searchable, risk-color-coded permission catalog grouped by area (tabs, storage, network, browser data, identity, and more)
Validation that catches Web-Store blockers like missing version and invalid V3 permissions, plus best-practice warnings
Switches every key correctly between Manifest V3 and V2 (action vs browser_action, service_worker vs background scripts, host folding)
One-click ZIP of a runnable unpacked extension with stub popup, background, content script, options, and DevTools files
Cross-browser notes for Firefox and Edge, plus a shareable URL that captures the whole manifest

Common Use Cases

Bootstrapping a new Chrome or Edge extension without copying boilerplate from old projects
Auditing how scary your permission set looks before publishing — tuning permissions until the install dialog reads cleanly
Migrating a Manifest V2 extension to V3 and seeing which keys change
Generating a loadable scaffold to test an idea in chrome://extensions in seconds
Teaching how Chrome permissions map to user-facing consent warnings
Producing a correct AppIcon-ready manifest skeleton to hand to a teammate via a single link

manifest.json

Copy, download, share, or pipe to another tool

{
  "manifest_version": 3,
  "name": "Popup Extension",
  "version": "1.0.0",
  "description": "A Chrome extension built with consolelog.tools",
  "icons": {
    "16": "icons/icon16.png",
    "32": "icons/icon32.png",
    "48": "icons/icon48.png",
    "128": "icons/icon128.png"
  },
  "action": {
    "default_popup": "popup.html",
    "default_title": "Open popup",
    "default_icon": {
      "16": "icons/icon16.png",
      "32": "icons/icon32.png",
      "48": "icons/icon48.png",
      "128": "icons/icon128.png"
    }
  },
  "permissions": [
    "storage",
    "activeTab"
  ]
}

Install permission preview

No warning prompt. Chrome installs this extension without a permission dialog.

Validation — all clear

This manifest passes every check — ready to load and publish.

Manifest version

Start from a template

Basics

Name*

Version

Description

46/132 chars shown in the store

Features

Action tooltip (default_title)

Options page

Permissions (2)

Tabs & windows

Storage & state

User interface

Scripting & content

Network

Browser data

Device & system

Identity & power

Host permissions

One match pattern per line. Drives the install-warning preview.

Content scripts (0)

No content scripts. Add one to inject JS/CSS into matching pages.

Keyboard shortcuts (0)

No commands. Add a shortcut to trigger the action or a custom event.

Web-accessible resources (0)

No web-accessible resources. Add files that pages are allowed to load.

Advanced & metadata

Short name

Version name

Author

Homepage URL

Default locale

Minimum Chrome version

Incognito mode

Content Security Policy (extension_pages)

Cross-browser (Firefox / Edge)

Add `browser_specific_settings: { "gecko": { "id": "[email protected]" } }` so Firefox/AMO can identify the add-on.
Edge runs Chromium manifests unchanged; publish the same package to the Edge Add-ons store.

See the consent dialog before your users do

Every permission you add is mapped to the exact warning Chrome shows at install time — host patterns become “Read and change your data on…”, broad access collapses to “…on all websites”, and overlapping warnings are deduped just like the real dialog. Tune permissions until the preview reads how you want, validate against the store rules, then download a runnable unpacked extension you can load straight into chrome://extensions.

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Related guide

Guide · 10 min readChrome Extension manifest.json: The Complete Manifest V3 Field GuideEvery manifest.json key explained: the three required fields, UI surfaces, service workers, content scripts, the three-way permission model and the install warnings it triggers, plus the exact MV2 to MV3 migration map now that Manifest V2 is fully gone.Read the guide

Chrome Extension Manifest Generator

How to Use

Key Benefits

Common Use Cases

Install permission preview

Validation — all clear

Manifest version

Start from a template

Basics

Features

Permissions (2)

Tabs & windows

Storage & state

User interface

Scripting & content

Network

Browser data

Device & system

Identity & power

Content scripts (0)

Keyboard shortcuts (0)

Web-accessible resources (0)

Cross-browser (Firefox / Edge)

See the consent dialog before your users do

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Frequently Asked Questions - Chrome Extension Manifest Generator