# x402 Counterparty Score

> Decision-grade counterparty scores for the x402 ecosystem, served to AI agents over MCP (Model Context Protocol) with per-call x402 payments (USDC). Input an x402 endpoint URL or pay-to address; output is a trust verdict (trusted/caution/avoid) with wash-trading ratio, real-buyer count, repeat-buyer rate, and provenance fields (source, updated_at, confidence).

All paths in this file are relative to this file's origin.

## Service

- MCP endpoint: send JSON-RPC 2.0 messages via POST /mcp (MCP Streamable HTTP). GET /mcp returns 405: the optional SSE notification stream is not offered; use POST.
- Payment: x402 protocol, USDC. Calling the paid tool without payment returns an in-band quote in the tool result's `_meta["x402/error"]` (an `accepts` array with scheme, network, asset, pay-to address, amount). Sign a payment authorization for one entry of `accepts`, base64-encode the x402 payment payload JSON, and call the tool again with it in `params._meta["x402/payment"]`. x402-aware MCP clients do this automatically.
- The in-band 402 quote is authoritative for price, asset, network, and pay-to address. The listed $0.02/call is the currently configured price.
- Error envelopes settle no payment: `ANSWER_UNAVAILABLE` (503 semantics; no fresh answer — missing, delisted, or older than 24h; stale answers are never sold) and `TOOL_DELISTED` (503 semantics; delisting is checked before any payment step) both carry machine-readable recovery instructions.
- Every successful response includes provenance: `source`, `updated_at`, `confidence`.

## Tools

- score_x402_counterparty (paid): Returns trust verdict (trusted/caution/avoid) with wash-trading ratio, real-buyer count, and repeat-buyer rate for an x402 endpoint URL or pay-to address. $0.02/call. Updated daily from Base on-chain settlement data and the x402 Bazaar catalog.
- get_sample_score (free): Returns a clearly-marked stale sample counterparty score in the exact response schema of score_x402_counterparty (verdict, wash_trading_ratio, real_buyer_count, repeat_buyer_rate, source, updated_at, confidence). Free, no payment required, no input required. Sample data is fixed and expired by design — use it to validate response parsing, then call score_x402_counterparty ($0.02/call) for fresh decision-grade scores.

## Documentation

- [OpenAPI specification](/openapi.json): machine-readable endpoint description, tool input/output JSON Schemas, x402 payment flow, error envelopes
- [Methodology](/methodology): deterministic scoring rules, data sources and licensing basis, confidence definition, coverage limits, probing and bootstrap-settlement disclosures
- [Landing page](/): service summary for humans verifying this service before funding an agent wallet