# Extension.dev platform documentation

> Extension.dev is the hosted platform that takes a finished browser extension from build to every browser's store. These docs cover the console, the publish rail, shared previews, and the agent tools: the MCP server, the agent skill, and the CLI.

Extension.dev sponsors Extension.js, the open source framework it builds on. The framework covers create, develop and build on your own machine, up to packaging, and is documented at https://extension.js.org. The platform begins where a workspace or an access token is minted, and that is what these docs describe.

extension.dev is not open to the public yet. Every page here is truthful about the platform. Signup and the hosted console answer that they are not open yet until it opens.

## Start here

What the platform is, and your first extension shipped to every browser.

- [Overview](https://docs.extension.dev): What Extension.dev is, the map of the docs, and where to go next.

## Agent tools and the CLI

What the platform gives a coding agent, and where the CLI mints a token.

- [MCP server](https://docs.extension.dev/tools/mcp): Give a coding agent the build, preview, release and publish verbs.
- [Server flags and telemetry](https://docs.extension.dev/tools/mcp/flags): The three flags that decide which MCP tools an agent sees, the approvals that wait for a person, the fence around page-written text, and the one telemetry event.
- [Platform tools](https://docs.extension.dev/tools/mcp/platform): Log an agent in to extension.dev, create several projects under one approval, share a build in progress, and keep publish and submit apart with the eleven platform tools.
- [Run on Safari](https://docs.extension.dev/tools/mcp/safari): Start a Safari dev session from an agent, turn on the one Safari setting it needs, and see which MCP tools work there and which Extension.js version each one needs.
- [Agent skill](https://docs.extension.dev/tools/skill): The judgment half of the agent stack, one skill in the open Agent Skills format.
- [Pair with Chrome DevTools MCP](https://docs.extension.dev/tools/chrome-devtools-mcp): Run Google's chrome-devtools-mcp and the extension.dev MCP server in one agent config, and know which one to reach for.
- [CLI](https://docs.extension.dev/tools/cli): The Extension.js command line, and the agent-facing package that reaches the platform.
- [Agent bridge](https://docs.extension.dev/tools/agent-bridge): The local channel that lets a terminal, a script or an AI agent observe a running extension and, per session, act on it.
- [Agent logs](https://docs.extension.dev/tools/logs): One ordered stream of everything the extension does, across every context, written to a local file and readable from the terminal or an agent.
- [Inspect and act](https://docs.extension.dev/tools/inspect-and-act): Read the live DOM of any surface and run scoped operations in the exact extension context you care about, on Chrome and Firefox.

## MCP tool reference

One page per MCP tool, generated from the server's schemas: inputs, gate, flags and a sample prompt, plus the install block for every client.

- ["extension_add_feature"](https://docs.extension.dev/tools/mcp/add-feature): "Plan the surface before adding an options page, a popup, a side panel, a content script, a devtools panel, a new tab page or a background script to an existing extension."
- ["extension_analyze"](https://docs.extension.dev/tools/mcp/analyze): "Analyze a BUILT extension on disk: file sizes, declared entry points, permissions, bundle composition, store-readiness checks, and manifestByBrowser, the emitted manifest of eve..."
- ["extension_assert"](https://docs.extension.dev/tools/mcp/assert): "Run a test stage against a live dev session: state expectations and read one verdict for each, instead of reading a blob and hand-rolling the judgement."
- ["extension_auth"](https://docs.extension.dev/tools/mcp/auth): "Sign this machine in to extension.dev, report that login, or clear it: action status (the default), login and logout."
- ["extension_browsers"](https://docs.extension.dev/tools/mcp/browsers): "Find, install and remove the browsers Extension.js tooling can launch."
- ["extension_build"](https://docs.extension.dev/tools/mcp/build): "Build a browser extension for production."
- ["extension_builds"](https://docs.extension.dev/tools/mcp/builds): "Read, rebuild and configure the platform's builds of the logged-in project on extension.dev: action list (the default), get, logs, recheck, rebuild, configure and create-channel."
- ["extension_create"](https://docs.extension.dev/tools/mcp/create): "Create a browser extension project from a template in the extension.dev catalog; call extension_templates first to see what is available."
- ["extension_dev"](https://docs.extension.dev/tools/mcp/dev): "Run the extension while you edit it: dev build, hot module replacement, and a browser with the extension loaded."
- ["extension_docs_search"](https://docs.extension.dev/tools/mcp/docs-search): "Find the docs page to cite before answering any question about a WebExtension API, a manifest key, a permission, or a difference between Chrome, Firefox, Edge and Safari."
- ["extension_doctor"](https://docs.extension.dev/tools/mcp/doctor): "Diagnose a dev session end to end: ready contract, dev-server process, control-port agreement, control channel, eval token, executor, browser liveness."
- ["extension_dom_snapshot"](https://docs.extension.dev/tools/mcp/dom-snapshot): "Take a shallow structured DOM snapshot of one chosen surface: element counts, extension roots, open shadow roots, optional byte-capped HTML, and optional recent console lines."
- ["extension_eval"](https://docs.extension.dev/tools/mcp/eval): "Evaluate an expression in a running extension context: the background, an extension surface (popup, options, sidebar, devtools, newtab, history, bookmarks), a content script or..."
- ["extension_inspect"](https://docs.extension.dev/tools/mcp/inspect): "Inspect a running extension deeply over the browser's debugger protocol: full HTML (open shadow roots of the extension-root hosts inlined; other shadow roots are not crossed by..."
- ["extension_list_extensions"](https://docs.extension.dev/tools/mcp/list-extensions): "List the extensions in the running dev browser: id, name, version, and, on Chromium, live contexts."
- ["extension_logs"](https://docs.extension.dev/tools/mcp/logs): "Read or stream logs from every context of a running dev session (service worker, content scripts, popup, options, sidebar, devtools, pages) in one ordered timeline."
- ["extension_manifest_validate"](https://docs.extension.dev/tools/mcp/manifest-validate): "Validate a manifest.json across browsers."
- ["extension_open"](https://docs.extension.dev/tools/mcp/open): "Open an extension surface (popup, options, sidebar, the newtab, history or bookmarks override page, or the extension's DevTools panel), navigate a tab to a url, or replay an eve..."
- ["extension_preview_web"](https://docs.extension.dev/tools/mcp/preview-web): "Preview a build in the web emulator and share it as a quick link anyone can open, with no install, sign-in or dev server."
- ["extension_project_create"](https://docs.extension.dev/tools/mcp/project-create): "Create an extension.dev project for an extension that does not have one yet, without opening the console: right after extension_create and extension_build, once the source is pu..."
- ["extension_publish"](https://docs.extension.dev/tools/mcp/publish): "Publish a build of the logged-in project on extension.dev and answer the link to send testers, which opens a page with a download and a run command for each browser."
- ["extension_release_promote"](https://docs.extension.dev/tools/mcp/release-promote): "Promote a built extension to a release channel (stable, preview, beta) on extension.dev, headless: action promote (the default) points channel at buildId, cut opens a release pu..."
- ["extension_release_status"](https://docs.extension.dev/tools/mcp/release-status): "Read where a project stands on extension.dev from the public registry (registry.extension.land): its release channels with each channel's audience and recent builds (include:'re..."
- ["extension_reload"](https://docs.extension.dev/tools/mcp/reload): "Reload a running extension's background context, or a tab."
- ["extension_screenshot"](https://docs.extension.dev/tools/mcp/screenshot): "Take a screenshot of one open extension surface (popup, options, sidebar, newtab, history, bookmarks) or web page in a live extension_dev or extension_start session and save it..."
- ["extension_shares"](https://docs.extension.dev/tools/mcp/shares): "List, create and revoke the emulator preview links that give a tester one build and its zip: the uploads this login has shared, the same links extension_preview_web share:true h..."
- ["extension_start"](https://docs.extension.dev/tools/mcp/start): "Run the PRODUCTION build in a browser: build the project, serve it, and launch."
- ["extension_stop"](https://docs.extension.dev/tools/mcp/stop): "Stop a session that extension_dev or extension_start is running: terminate the server and the browser it launched, and remove the live-preview carrier if extension_dev placed one."
- ["extension_storage"](https://docs.extension.dev/tools/mcp/storage): "Read or write chrome.storage in a running extension."
- ["extension_submit"](https://docs.extension.dev/tools/mcp/submit): "Submit a built extension to a store's review through extension.dev, which holds the store credentials and runs the upload on the platform (Chrome Web Store, Firefox AMO, Edge Ad..."
- ["extension_templates"](https://docs.extension.dev/tools/mcp/templates): "Browse the extension.dev template catalog."
- ["extension_theme_verify"](https://docs.extension.dev/tools/mcp/theme-verify): "Verify a Chrome theme manifest before it ships."
- ["extension_wait"](https://docs.extension.dev/tools/mcp/wait): "Wait for a running dev or start session to be ready, or for a rebuild after a source edit (for: \"rebuild\")."
- ["extension_workspace"](https://docs.extension.dev/tools/mcp/workspace): "Read the extension.dev workspace a stored login belongs to: its plan and limits, its projects, and its usage."
- ["extension_workspace_create"](https://docs.extension.dev/tools/mcp/workspace-create): "Create an extension.dev workspace that does not exist yet, without opening the console."
- ["Install in your client"](https://docs.extension.dev/tools/mcp/clients): "The MCP server's install line and config block for every client, with the local-only variant beside the full one."

## Templates

The six default starters and the full catalog, each created from the terminal, from an agent, or from templates.extension.dev.

- [Templates](https://docs.extension.dev/templates/): Six default starters and a catalog of 59 working extensions, each created from the terminal, from an agent, or from templates.extension.dev.
- [JavaScript template](https://docs.extension.dev/templates/javascript): A sidebar panel and a content script in JavaScript, created in one command from the terminal, from an agent, or from the catalog.
- [TypeScript template](https://docs.extension.dev/templates/typescript): A sidebar panel and a content script in TypeScript, created in one command from the terminal, from an agent, or from the catalog.
- [React template](https://docs.extension.dev/templates/react): A sidebar panel and a content script in React, created in one command from the terminal, from an agent, or from the catalog.
- [Preact template](https://docs.extension.dev/templates/preact): A sidebar panel and a content script in Preact, created in one command from the terminal, from an agent, or from the catalog.
- [Vue template](https://docs.extension.dev/templates/vue): A sidebar panel and a content script in Vue, created in one command from the terminal, from an agent, or from the catalog.
- [Svelte template](https://docs.extension.dev/templates/svelte): A sidebar panel and a content script in Svelte, created in one command from the terminal, from an agent, or from the catalog.

## More

- [Use the platform from your agent](https://docs.extension.dev/tools/mcp/platform-from-your-agent): Sign an agent in to one project or a whole workspace, see what its login reads and does, and which acts wait for an owner's approval.

## Related

- [Extension.js framework docs](https://extension.js.org): The free, open source framework the platform sponsors. It covers create, develop and build on your own machine, up to packaging.
- [Agent skill, installable by URL](https://docs.extension.dev/.well-known/skills/index.json): The @extension.dev/skill package served in the open Agent Skills layout, so `npx skills add https://docs.extension.dev` installs it once the site opens; until then the skill files hold with the fleet and `npx skills add extensiondev/skill` installs the same skill from GitHub.