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

MCP server score License: MIT Model Context Protocol

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

	Without `EVM_PRIVATE_KEY`	With `EVM_PRIVATE_KEY`
Free tools	Yes	Yes
Paid tools	No (tools visible but calls fail)	Yes (auto-pays via x402)

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)

Tool	What it does
`gauge_catalog`	Browse 180+ available signals
`gauge_preview`	Coverage, pricing menu, bundle contents
`gauge_sample`	Full sample record with Bitcoin receipt
`gauge_river_free`	US river gauge reading (USGS) with receipt
`gauge_anchor`	Look up Bitcoin proof for any `record_hash`

Paid — single-source verification

Tool	What it does
`verify_signal`	Check one official fact from 180+ signals. Bitcoin-anchored receipt.
`gauge_flood_risk`	Hydrology / air / precipitation alias of `verify_signal`
`gauge_resolution_as_of`	Prediction-market settlement — official fact + evidence + receipt

Paid — 3-source cross-validation bundles

Tool	What it cross-checks
`gauge_region`	Air quality + precipitation + river level
`gauge_crop_drought`	Drought severity + heat/GDD + satellite crop health
`gauge_grid_stress`	Demand pressure + renewable output + energy inflation
`gauge_route_disruption`	Sea state + wave cause + live AIS vessel traffic
`gauge_filing_check`	SEC 8-K events + late filing + insider buy/sell
`gauge_stablecoin_lifecycle`	Peg drift + redemption acceleration + protocol exposure
`gauge_rwa_lifecycle`	Issuer lifecycle + redemption pressure + downstream exposure
`gauge_lrt_lifecycle`	Discount-to-NAV + withdrawal queue + collateral cascade
`gauge_defi_lending`	Utilization + bad-debt pressure + contagion
`gauge_depin_network`	Network liveness + reward churn + downstream exposure

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

Key	Required	Description
`EVM_PRIVATE_KEY`	For paid tools	Base-mainnet wallet private key (0x...). Needs USDC, no ETH.
`GAUGE_BASE_URL`	No	API endpoint. Default: `https://api.truthbear.co`
`GAUGE_MAX_USDC`	No	Atomic per-call cap in USDC (6 decimals). Default: `350000`

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.