ProofCheck MCP

ProofCheck is a free, read-only verifier for x402 signed offers and receipts that validates signatures and checks for evidence binding the signing key to the service via did:web, DNS, or ERC-8004. It provides verdicts on authorization strength and supports remote MCP tools for verification tasks without requiring API keys or performing payments.

Endpoint and access

No sign-in to connect and list tools. Individual tools may still need a vendor account, credentials, or permissions; check the documented prerequisites.

Community listingStreamable HTTPNo sign-inEndpoint checked 2026-11-01Published by something

MCP endpoint (Streamable HTTP)

https://proofcheck.something-agent.workers.dev/mcp

Vendor documentation

What you can do with it

Verify x402 signed offers and receipts
Check if a signing key is authorized for a service
Preflight check x402 endpoints
Lookup ERC-8004 agent identity

Source and maintenance

Community listingRegistry 0.1.0

mcp-registry: io.github.something-agent/proofcheck@0.1.0 Source repository Project website

Maintenance checked: Nov 1, 2026, 8:12 AM UTC

Protocol and capabilities

Server: proofcheck 0.1.4
MCP protocol: 2025-06-18
Tools: 5 advertised
Resources: Not advertised
Resource templates: Not advertised
Prompts: Not advertised

Server-advertised capabilities

{
  "tools": {
    "listChanged": false
  }
}

Server-provided instructions

Untrusted server output shown for inspection. It is not Koskamo guidance and is excluded from knowledge search.

Free, read-only verification of x402 signed offers and receipts, with evidence on whether the signing key is authorized for the service. Never pays or signs.

Tools

5 advertised

verify_offer

Advertised by the server during the last successful anonymous check.

Verify an x402 signed offer (EIP-712 or JWS): signature, expiry, match to accepts[], and signer-authorization evidence (payTo, did:web, DNS _controllers, ERC-8004). Free.

verify_offer input schema

{
  "type": "object",
  "required": [
    "offer"
  ],
  "properties": {
    "offer": {
      "type": "object",
      "description": "The offer object: {format, payload?, signature, acceptIndex?}"
    },
    "accepts": {
      "type": "array",
      "items": {
        "type": "object"
      },
      "description": "Optional accepts[] from the live 402 to match against"
    },
    "resource_url": {
      "type": "string"
    },
    "trusted_pay_to": {
      "type": "array",
      "items": {
        "type": "string"
      }
    }
  }
}

verify_receipt

Advertised by the server during the last successful anonymous check.

Verify an x402 signed receipt (EIP-712 or JWS) returned in the settlement response: signature, freshness, payer/resource/transaction match, signer-authorization evidence. Free.

verify_receipt input schema

{
  "type": "object",
  "required": [
    "receipt"
  ],
  "properties": {
    "payer": {
      "type": "string"
    },
    "network": {
      "type": "string"
    },
    "receipt": {
      "type": "object"
    },
    "transaction": {
      "type": "string"
    },
    "resource_url": {
      "type": "string"
    },
    "trusted_pay_to": {
      "type": "array",
      "items": {
        "type": "string"
      }
    },
    "max_age_seconds": {
      "type": "number"
    }
  }
}

verify_payment_required

Advertised by the server during the last successful anonymous check.

Verify every signed offer inside a PaymentRequired object (pass the decoded JSON, or the raw base64 PAYMENT-REQUIRED header). Free.

verify_payment_required input schema

{
  "type": "object",
  "required": [
    "payment_required"
  ],
  "properties": {
    "resource_url": {
      "type": "string"
    },
    "payment_required": {
      "description": "Object or base64/JSON string"
    }
  }
}

preflight_x402_endpoint

Advertised by the server during the last successful anonymous check.

Unpaid preflight of an x402 URL: fetch its 402, summarise accepts[]/extensions, verify any signed offers and report who can vouch for the signer. Never pays. Free.

preflight_x402_endpoint input schema

{
  "type": "object",
  "required": [
    "url"
  ],
  "properties": {
    "url": {
      "type": "string"
    },
    "method": {
      "enum": [
        "GET",
        "POST"
      ],
      "type": "string"
    }
  }
}

lookup_erc8004_agent

Advertised by the server during the last successful anonymous check.

Read-only ERC-8004 identity lookup (owner, agentWallet, registration file, endpoint-domain verification) on Ethereum, Base, Optimism, Arbitrum, Polygon, BNB, Avalanche, Gnosis, Celo, Linea or Scroll.

lookup_erc8004_agent input schema

{
  "type": "object",
  "required": [
    "chain_id",
    "agent_id"
  ],
  "properties": {
    "agent_id": {
      "type": "string"
    },
    "chain_id": {
      "type": "integer"
    }
  }
}

Prompts

Not advertised

No prompt definitions available.

Resources

Not advertised

No resource definitions available.

30-day availability

Aggregated from read-only remote checks; this is not a tool-execution or security guarantee.

Successful checks: 1 of 1 (100%)
Average latency: 211 ms
95th percentile latency: 211 ms

Maintenance history

Public check and source-refresh events. Editorial and ownership records remain private.

Nov 1, 2026, 8:39 AM UTC · probe · passed · 211 ms · metadata changed · 5 tool(s)

Connect from your client

Each snippet registers the same endpoint; pick the client you use.

This server is operated by the named third party. Listing and endpoint checks are not an endorsement or a security audit. Review the operator's permissions, terms, and data handling before connecting. How listings are checked and corrected.

Claude Code

Run this once in a terminal. It registers the remote server. Use --scope project to write .mcp.json for the repo.

Claude Code configuration

claude mcp add --transport http proofcheck-mcp https://proofcheck.something-agent.workers.dev/mcp

Codex

Run this once. Codex stores MCP servers in ~/.codex/config.toml (or .codex/config.toml in a trusted project).

Codex configuration

codex mcp add proofcheck-mcp --url https://proofcheck.something-agent.workers.dev/mcp

Cursor

Merge this server into .cursor/mcp.json in your project, then enable proofcheck-mcp in your MCP settings.

Cursor configuration

{
  "mcpServers": {
    "proofcheck-mcp": {
      "url": "https://proofcheck.something-agent.workers.dev/mcp"
    }
  }
}

Cline

Merge this into cline_mcp_settings.json (Cline → MCP Servers → Configure).

Cline configuration

{
  "mcpServers": {
    "proofcheck-mcp": {
      "type": "streamableHttp",
      "url": "https://proofcheck.something-agent.workers.dev/mcp",
      "disabled": false
    }
  }
}

VS Code

Merge this server into .vscode/mcp.json. Use MCP: List Servers to start proofcheck-mcp and inspect its tools.

VS Code configuration

{
  "servers": {
    "proofcheck-mcp": {
      "type": "http",
      "url": "https://proofcheck.something-agent.workers.dev/mcp"
    }
  }
}

Gemini CLI

Run this once. It writes .gemini/settings.json in the current project; pass --scope user for ~/.gemini/settings.json.

Gemini CLI configuration

gemini mcp add --transport http proofcheck-mcp https://proofcheck.something-agent.workers.dev/mcp

Claude Desktop

Merge this into claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\), then restart Claude Desktop.

Claude Desktop configuration

{
  "mcpServers": {
    "proofcheck-mcp": {
      "url": "https://proofcheck.something-agent.workers.dev/mcp"
    }
  }
}

Windsurf

Merge this into ~/.codeium/windsurf/mcp_config.json, then refresh MCP in Cascade. Windsurf remote servers use serverUrl, not url.

Windsurf configuration

{
  "mcpServers": {
    "proofcheck-mcp": {
      "serverUrl": "https://proofcheck.something-agent.workers.dev/mcp"
    }
  }
}

Let your agent find its tools

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