extension_preview_web

Preview an in-progress extension in the web emulator, with no real browser.

Quick start

Share this build with my designer

How the agent uses it

This builds the project (unless build:false) and previews dist/<browser>. Pass share:true unless you are working inside the extension.dev monorepo: it uploads the build and returns a link anyone can open, with no install, sign-in or dev server, and it is the only lane that works from an npm install of this server. Sharing also serves the build as a zip, so it hands over the built code; read the share property before using it. The default lane instead returns a deep link over the dev-only preview://build scheme, which resolves only against a preview.extension.dev dev server on this machine, so it is for people developing extension.dev itself. Call extension_shares to list and revoke every link shared this way, so one never vanishes with this response.

Reference

Group	platform, on with --features=local,platform (private alpha)
Tier	Platform
Needs	the server started with --features=local,platform; sharing needs a login
Read only	no
Destructive	no
Idempotent	no
Reaches the open web	yes

Inputs

Input	Type	Required	Default	What it does
projectPath	string	yes		Extension project root
project	string	no		Which stored login to use, as '<workspace>/<project>' (or a project slug that matches one login), when extension_auth has signed in to more than one project on this machine. Omitted, the most recent login is used, after EXTENSION_DEV_TOKEN when that is set. Named, it outranks EXTENSION_DEV_TOKEN. extension_auth (action: status) lists the stored logins.
browser	"chrome" | "chromium" | "edge" | "brave" | "opera" | "vivaldi" | "yandex" | "firefox" | "waterfox" | "librewolf" | "zen" | "floorp" | "safari"	no	"chrome"	Which dist/<browser> output to preview. The emulator renders it as mocked Chrome either way.
build	boolean	no	true	Build first. false previews the existing dist/<browser> as-is.
distPath	string	no		Preview this built directory instead of dist/<browser> under projectPath. Implies build:false.
hostUrl	string	no		Origin of the running preview.extension.dev dev server (default http://localhost:3110).
probe	boolean	no	true	Fetch the surface's dev middleware first to confirm the artifact loads on the local host. With share:true it also checks the shared link the way a browser would, following the zip's redirects and asserting the final response allows the preview origin, and reports that as share.browserLoadable.
open	boolean	no	false	Also open the deep link in a running session's browser, in a focus-safe background tab. Needs a live extension_dev/extension_start session.
openIn	"chrome" | "chromium" | "edge" | "brave" | "opera" | "vivaldi" | "yandex" | "firefox" | "waterfox" | "librewolf" | "zen" | "floorp" | "safari"	no		Which session's browser to open it in. Defaults to browser.
share	boolean	no	false	Upload the built dist and return a public link (share.previewUrl) that renders those exact bytes for anyone: no install, sign-in or dev server. Uploading is metered against your plan's allowance on extension.dev; left false, the result's share property says what the local deepLink needs, what share:true spends, and the exact call to get a shareable link. It also serves the build as a zip (share.zipUrl), so sharing hands over the code. Needs a token scoped to an extension.dev project (extension_auth or EXTENSION_DEV_TOKEN); without one you get a login hint and the local preview still succeeds. Live until share.expiresAt; DELETE share.revokeUrl to kill it sooner. Revocation is permanent, and re-sharing an unchanged build returns the same link unless it was revoked, so each share is also appended to the project's gitignored .extension.dev/shared-previews.json.

When it fails

• The tool is missing from the client's list. Start the server with --features=local,platform; see Platform tools.
• The platform refuses the call. Log in first with extension_auth.
• The answer reads status: "platform-held". extension.dev is not open to the public yet, so nothing ran on its machines. Creating, running and building an extension still work on your machine; see Use the platform from your agent.
• The answer depends on the network. This tool reaches the open web, so a refusal can be the network, not the project.

Next

• MCP server: install, the two groups and the session gates
• Install in your client
• extension_auth: Sign this machine in to extension.dev, report that login, or clear it.
• extension_builds: Read, rebuild and configure the platform's builds of the logged-in project on extension.dev.
• extension_project_create: Create an extension.dev project for an extension that does not have one yet, without opening the console.
• extension_publish: Publish the project your stored token is scoped to (extension_auth, or EXTENSION_DEV_TOKEN) to extension.dev, and return its shareable URL.
• extension_release_promote: Promote a built extension to a release channel (stable, preview, beta, …) on extension.dev, headless.
• extension_release_status: Read where a project stands on extension.dev, from the public registry (registry.extension.land).
• extension_shares: List, create and revoke the public preview links this token has shared, which is what extension_preview_web share:true hands out.
• extension_submit: Submit a built extension for store REVIEW through extension.dev, which holds your store credentials and dispatches from your project's mirror CI: the Chrome Web Store, Firefox A...
• extension_workspace: Read the extension.dev workspace a stored login belongs to: its plan and limits, its projects, and its usage.
• extension_workspace_create: Create an extension.dev workspace that does not exist yet, without opening the console.