Housecarl
Housecarl Arbiter
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Use it from Google Antigravity

Connect Housecarl Arbiter to Google Antigravity so Antigravity's agent can gather evidence, run investigations, and return scored verdicts — all in one pass.

What you need

  • A Housecarl Arbiter account (free tier works)
  • An Arbiter API key — create one in Connection under API Keys. Copy it at creation; it is shown once.

Add Arbiter as an MCP server

In Google Antigravity, open your MCP server configuration and add the following entry. Antigravity uses serverUrl (not url) as the key name:

{
  "mcpServers": {
    "Housecarl Arbiter": {
      "serverUrl": "https://api.arbiter.housecarl.cloud/mcp/v1",
      "headers": {
        "x-api-key": "YOUR_API_KEY"
      }
    }
  }
}

Replace YOUR_API_KEY with the key you just created.

Try it

Once connected, Antigravity can reach Arbiter's MCP tools directly. A prompt like this sends the full pipeline in one shot:

"Pull down https://en.wikipedia.org/wiki/Cold_fusion and find all the claims it makes. Then go search all the evidence it cites, and go looking for supporting or denying evidence. After that, feed it all into the Housecarl Arbiter research system."

Antigravity will read the document, extract claims and evidence, search for corroboration, and submit the full investigation to Housecarl Arbiter for formal reasoning analysis.

Results land in your Sessions — one session per investigation, with the full scored verdict and reasoning trace.

Configuration note

Standard MCP clients (Claude Code, Cursor, Windsurf) use url as the key. Google Antigravity uses serverUrl. If you paste a config from another client it will silently fail to connect — swap url → serverUrl and it works.

Reference