Antigravity MCP setup: add an MCP server

Add an MCP server to Google Antigravity: mcp_config.json with serverUrl, agy mcp add, why the token must be literal, and how to see it loaded.

Last updated Sep 22, 2026

Antigravity keeps one MCP configuration for the IDE, the app and the CLI together. Its remote-server entry uses serverUrl rather than the url most other clients expect.

The worked example is Scalebrowser's own server, which gives the agent a real browser on your machine. Any other HTTP MCP server takes the same entry with its own address.

Before you start

Everything below assumes a daemon that is already running and a token to reach it with.

Windows desktop app

The app starts the daemon for you. The token is the contents of %LOCALAPPDATA%\Scalebrowser\token, and the address it is listening on is the native_addr field of %LOCALAPPDATA%\Scalebrowser\runtime.json. That is usually 127.0.0.1:8787, but the app moves up a port when something else already holds it.

Self-hosted daemon

scalebrowser-daemon --generate-token prints a token and stores it under <data_dir>/token. The address is whatever bind_addr says, which is 127.0.0.1:8787 unless you changed it. See Install & run.

The token is a full-power credential. It reaches every profile, every stored session and the whole management API. Treat it like a password and keep it out of a repository. Antigravity has no way to read it from the environment, so the file that holds it is the one thing to protect.

Add the server

~/.gemini/config/mcp_config.json is the file the IDE, the Antigravity app and the agy CLI all read. A workspace can carry its own .agents/mcp_config.json, but the CLI has been reported to ignore it (an open issue in September 2026), so the global file is the one that works everywhere.

~/.gemini/config/mcp_config.jsonjson

{
  "mcpServers": {
    "scalebrowser": {
      "serverUrl": "http://127.0.0.1:8787/v1/mcp",
      "headers": {
        "Authorization": "Bearer <token>"
      }
    }
  }
}

The token has to be written into the file. Antigravity does not expand environment variables in mcp_config.json: a header of Bearer ${SCALEBROWSER_TOKEN} is sent as exactly that text, and the daemon answers Unauthorized. Keep this file out of any repository, and never put a token into the workspace copy.

The CLI writes the same entry. Flags go before the name:

bash

agy mcp add --header "Authorization: Bearer <token>" scalebrowser http://127.0.0.1:8787/v1/mcp

In the IDE you can reach the same file without leaving the editor: … at the top of the agent panel → MCP Servers → Manage MCP Servers → View raw config. The MCP Store opens from the same MCP Servers menu; a server you run yourself is added here, not there.

Write serverUrl. Current builds also accept url, older ones read an entry with url as a different shape and never load it. serverUrl works on every version, and it is what agy mcp add writes.

Check that it loaded

CLI: agy mcp list prints each server with its type and status. Inside a session, /mcp opens the manager with a status per server, a reload and the logs.
Antigravity app: Settings → Customizations → Installed MCP Servers, with a toggle and a refresh per server.
IDE: MCP Servers → Manage MCP Servers lists what loaded.

New MCP tools start on Ask, so the first call of each asks for permission. Antigravity speaks stdio, Streamable HTTP and SSE.

When it does not load

Antigravity says	What to do
`Unauthorized`	The header did not carry the real token, most often because it was written as a variable. Put the token in literally.
`must have either command or serverUrl`	The entry uses a key this build does not know, such as `httpUrl`. Rename it to `serverUrl`.
`cannot have both command and serverUrl`	One entry mixes a local command with a remote address. Keep `serverUrl` only.
The server is missing from the list	It sits in the workspace file. Move it to `~/.gemini/config/mcp_config.json`.

What the agent can do now

Ask it to open a page and it will lease a profile, bind a tab and start reading. The tool set, the page map and the failure shapes are on MCP server; what the agent is allowed to do is decided by the daemon, not by the client, so see tool profiles.

Run it on your own machine

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