clearsigned-mcp

An MCP server that gives any agent a verify_claim tool: calibrated claim verification against live web evidence, paid per call over x402 ($0.05 USDC on Base), with an Ed25519-signed receipt the server verifies offline against Clearsigned's pinned published key before your agent sees it.

Tools

UNVERIFIABLE is a real answer, not an error: the engine abstains instead of guessing. The price never depends on the verdict; refunds exist only for failure to deliver. A request with no claim is refused locally, before any payment.

Install

pip install clearsigned-mcp        # or: pipx install clearsigned-mcp
export CLEARSIGNED_BUYER_KEY=0x…   # an EVM key holding a little USDC on Base mainnet
clearsigned-mcp                    # stdio transport

Claude Desktop / Claude Code / any MCP client:

{
  "mcpServers": {
    "clearsigned": {
      "command": "clearsigned-mcp",
      "env": { "CLEARSIGNED_BUYER_KEY": "0x…" }
    }
  }
}

The key is used only to sign x402 payment authorizations from your own wallet. It is never sent to Clearsigned; the service sees the payment, not the key.

How to check us

• Pin the key at https://verify.clearsigned.com/pubkey; this server does, and refuses a receipt whose signature does not verify against it.
• Walk the public hash-chained ledger at https://verify.clearsigned.com/ledger/verify; every paid receipt and its on-chain settlement are separate events joined on payer and nonce.
• Read the live figures at https://clearsigned.com/quality (counts and timings, never a claim) and the serving calibration curve at https://clearsigned.com/stats.json.

Source of truth

This package is developed inside the Clearsigned monorepo (products/mcp-server/) and mirrored to a public repository for registries and installs. Issues and pull requests on the mirror are welcome; changes land in the monorepo first.

Development

python -m pytest tests/

The tests never touch the network or a wallet: the exchange is injected, and receipts are signed with a throwaway Ed25519 key to exercise the offline verification exactly as production does it.