mcp-gauge — Verifiable facts for AI agents, pay-per-call via x402

Check official facts before your AI agent acts. 180+ signals from USGS, NOAA, SEC EDGAR, EPA, and more — each response includes multi-source cross-validation and a tamper-proof receipt anchored to Bitcoin via OpenTimestamps. No API key, no signup. Pay per call in USDC on Base via x402.

Quick start

Claude Desktop

Add to your config (`~/Library/Application Support/Claude/claude_desktop_config.json` on macOS, `%APPDATA%\Claude\claude_desktop_config.json` on Windows):

{
  "mcpServers": {
    "gauge": {
      "command": "npx",
      "args": ["-y", "mcp-gauge-x402"],
      "env": {
        "EVM_PRIVATE_KEY": "0x..."   // optional — omit for free tools only
      }
    }
  }
}

Cursor

Add to `.cursor/mcp.json` in your project root (or global config):

{
  "mcpServers": {
    "gauge": {
      "command": "npx",
      "args": ["-y", "mcp-gauge-x402"],
      "env": {
        "EVM_PRIVATE_KEY": "0x..."   // optional — omit for free tools only
      }
    }
  }
}

Claude Code

claude mcp add gauge -- npx -y mcp-gauge-x402
# For paid tools, add the env:
claude mcp add gauge --env EVM_PRIVATE_KEY=0x... -- npx -y mcp-gauge-x402

Other MCP hosts

Any MCP client that supports stdio transport works. Command: `npx -y mcp-gauge-x402`, set `EVM_PRIVATE_KEY` in env for paid tools.

> Alternative: install from GitHub (no npm account needed):

> ```

> npx -y github:CHANGCHINFU/mcp-gauge

> ```

From source

git clone https://github.com/CHANGCHINFU/mcp-gauge && cd mcp-gauge
npm install && npm run build
node dist/index.js

Payment setup

How it works: When your agent calls a paid tool, the GAUGE server returns an x402 payment challenge. The MCP client automatically pays in USDC on Base (EIP-3009 gasless — no ETH needed) and retries the request. The receipt is included in every response.

Wallet safety:

• Use a dedicated burner wallet with a small USDC balance — never your main wallet
• The private key never leaves your machine (processed locally by `x402-fetch`)
• Fund with just enough USDC for your expected usage
• Network: Base mainnet (Coinbase L2)

Tools

Free (no wallet needed)

Paid — single-source verification

Paid — 3-source cross-validation bundles

Prices are set by the live x402 challenge (use `gauge_preview` to check current pricing). If you drive the API with your own x402 client, set `maxValue` to at least $0.25 — the default $0.10 makes your client reject bundle tools locally.

Environment variables

Zero-trust verification

Every paid record carries a `record_hash` (canonical SHA-256). Daily Merkle roots are stamped to Bitcoin via OpenTimestamps. The stamp proves the record set existed no later than `stamped_at`. Re-check anytime:

• `gauge_anchor` tool (free)
• `POST /verify` or `/proof/:record_hash` at the GAUGE API
• Download attestation bytes and verify with the official `ots` CLI

FAQ

Do I need ETH for gas?

No. x402 uses EIP-3009 (gasless USDC transfer). You only need USDC on Base.

What if I don't set a private key?

You can still use all 5 free tools. Paid tools will be listed but return an error when called.

Is my private key sent to the server?

No. The key stays on your machine. `x402-fetch` signs the payment locally and sends only the signed authorization to the GAUGE server.

What happens if the data isn't available?

The tool honest-fails with no charge. You only pay when you get a result.

Can I verify the receipt without your server?

Yes. Download the OpenTimestamps attestation via `gauge_anchor` and verify with the standard `ots` CLI tool against any Bitcoin node.

Links

• Website: truthbear.co
• Front desk: gauge-frontdesk.zeabur.app
• API discovery: `https://api.truthbear.co/.well-known/x402`, `/llms.txt`
• Smithery: smithery.ai/servers/a98741263/mcp-gauge
• GitHub: CHANGCHINFU/mcp-gauge

MIT · AEML-DS Vanished-Data Exchange