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 (proving the record set existed no later than the stamp time, not that it was collected on the data day). 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):

Terminal

Copy

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 — it proves the record set existed no later than the stamp time, not that it was collected on the data day.

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