extension_try
Run a published extension.dev build for the person in a fresh browser on this machine, so they see it work without downloading a package, turning on developer mode or running an installer.
Quick start
Try cezaraugusto/rebeccat for me and show me what it does
How the agent uses it
It downloads the build's package (newest by default), checks it against the platform's integrity record when there is one, unpacks it into a temporary folder and launches it with a new profile; on Extension.js 4.1.34 or later it then opens the popup or replays the toolbar action and saves a screenshot, and on an older engine it only launches and says the extension was not used. The answer names the version, the package size, what was confirmed and what was not, the screenshot, and what the extension can reach in plain words: warn the person about that. Nothing stays installed: call it again with action:'close' when done. For a project on disk use extension_dev or extension_start.
Page text in the answer
Part of this tool's answer is text a web page or the extension wrote. The server fences it between <untrusted-data-ID> and </untrusted-data-ID> with a fresh random ID per call, named in untrusted.boundary. A fence is a signal to the model, not a gate: pair it with --no-ship when the agent reads pages you do not trust. See Server flags and telemetry.
Reference
| Group | local, on by default |
| Tier | Run |
| Needs | none |
| Read only | no |
| Destructive | no |
| Idempotent | no |
| Reaches the open web | yes |
Inputs
| Input | Type | Required | Default | What it does |
|---|---|---|---|---|
project | string | yes | The published project as "<workspace>/<project>", the two names in its extension.dev address <workspace>.extension.dev/<project>. | |
version | string | no | The version to run (0.3.0), or a build sha or its first characters (6b393ca). Omitted, the newest successful build that has a package for the browser. | |
browser | string | no | "chrome" | chrome, edge or firefox. safari is refused: its package is an app that needs signing and a manual enable in Safari's settings. |
url | string | no | The http or https page to open with the extension. Omitted, the browser opens about:blank: no sample page ships with this server. | |
headless | boolean | no | true | true runs the browser with no window, which never takes the person's keyboard. false opens a window they can see and use. |
action | "run" | "close" | no | "run" | run downloads and launches. close ends every try of this project (one browser with browser) and deletes its folder and profile; screenshots stay. |
When it fails
- 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_dev: Run the extension while you edit it: dev build, hot module replacement, and a browser with the extension loaded.extension_start: Run the PRODUCTION build in a browser: build, serve and launch.extension_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_wait: Wait for a running dev or start session to be ready, or for a rebuild after a source edit (for: "rebuild").