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Add a remote MCP server to Antigravity

Updated

Antigravity’s agent can call remote MCP servers. This guide connects BRONTIR, live web research with citations from search to Reddit, YouTube and reviews, in the Antigravity app, with the IDE’s menu path alongside. It covers what trips people up: a server that isn’t in the MCP store goes into mcp_config.json by hand, the sign-in ends with an authorization code you paste back, and some versions stop at “Unauthorized” before it starts.

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Antigravity MCP setup, step by step

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Added through the MCP config file.

  1. Press Settings at the bottom left, then Customizations. Under Installed MCP Servers, press Open MCP Config, or open ~/.gemini/config/mcp_config.json yourself.
  2. Add this and save. If the file already lists servers, put research inside its mcpServers:
    { "mcpServers": { "research": { "serverUrl": "https://research.brontir.com/api/mcp" } } }
  3. Press Refresh next to Add MCP. The server shows an Unauthorized error until you sign in: press Authenticate next to it.
  4. Sign in with your Google account and press Approve. Copy the authorization code the next page shows, paste it into the box under the server and press Submit.

Recent versions take url as well as serverUrl, and serverUrl works on every version. In the Antigravity IDE, open the file from the agent side panel (… → MCP Servers → Manage MCP Servers → View raw config) and sign in from Agent Settings (Ctrl + ,) → Customizations.

Always restart your client after connecting. Quit and reopen the desktop app, or reload the page in a web client. Clients read the tool list once at startup, so until they restart your agent may not see the new tools even though the connector already shows as connected.

Antigravity MCP troubleshooting

  • The connector is connected, but the agent doesn't see the tools. Restart the client: quit and reopen the desktop app, or reload the page in a web client. If the tools are still missing, start a new chat, since an open conversation can keep the tool list it was created with.
  • You pressed Approve, but the client still shows the connector as not connected. Authorization did go through; the client just hasn't refreshed its own state. Restart the app or reload the page and it will show as connected. If it doesn't, press Connect once more and approve again.
  • The agent uses its built-in web search instead of these tools. Name the tools in your prompt: “use advanced_web_search and advanced_web_fetch from the research MCP” rather than “look this up”. To make it permanent, add it as a global rule in Antigravity’s Rules (+ Global), which writes it to ~/.gemini/GEMINI.md.

Full setup guide for every client: brontir.com/docs.

Antigravity MCP: common questions

Where is the MCP config in Antigravity?

In the app: Settings at the bottom left → Customizations, then Open MCP Config under Installed MCP Servers. In the IDE: … → MCP Servers → Manage MCP Servers → View raw config, in the agent side panel. Both open ~/.gemini/config/mcp_config.json, and a project can have its own in .agents/mcp_config.json.

Why doesn’t Antigravity pick up my server?

The list doesn’t reload by itself: press Refresh next to Add MCP, under Installed MCP Servers, or restart Antigravity. If the server still doesn’t appear, check the file is valid JSON with a single mcpServers object: { "mcpServers": { "research": { "serverUrl": "https://research.brontir.com/api/mcp" } } }. Recent versions of the app and the IDE take url as well, but serverUrl works on every version, the command-line agent included.

How does the sign-in finish?

Press Authenticate next to the server in Settings → Customizations (Agent Settings, Ctrl + ,, in the IDE), sign in with Google in the browser, copy the authorization code it gives you, paste it into the box under the server and press Submit. A Sign out button next to the server means you’re connected.

Antigravity shows “Unauthorized” and there is no Authenticate button. What now?

Some Antigravity versions fail the browser sign-in for remote servers: the server stops at calling "initialize": Unauthorized, and its menu offers only Restart and Disable. Connect with an API key instead. Create one on the API keys panel of your BRONTIR account and add it as a header: { "mcpServers": { "research": { "serverUrl": "https://research.brontir.com/api/mcp", "headers": { "Authorization": "Bearer nai_…" } } } }. The command-line agent takes the same header: agy mcp add -H "Authorization: Bearer nai_…" research https://research.brontir.com/api/mcp.

Once connected

What your agent can do with BRONTIR

  • Search the web and the news, Reddit, YouTube, TikTok and other social platforms.
  • Read whole pages, PDFs, video transcripts and comment threads, not snippets.
  • Pull reviews, maps and local businesses, app stores, products and ad libraries.
  • Get it all back structured, with citations down to the exact line.
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