P0: sanctions, KYB and payee checks

by dev.workers.x402-bazaar-rank-worker.x402-bazaar-rank

Check counterparty

check_counterparty

Read-onlyIdempotent

Use when you must vet a counterparty before paying or onboarding it: one call screens a name (and an optional wallet address) against OFAC SDN, UK, EU, Canada and US CSL. Returns the paid x402 request for your input (GET /check/counterparty, $0.015 per call; schema linked). Call that URL with an x402 or MPP client to get the data. Bad input is refused before any charge. Sanctions part: UK and Canada: organisations and wallets only. A name, optionally with country, LEI or wallet address; for one payee address before paying use check_payee; for a plain list lookup of an address or name use sanctions_screening. With an access key (Authorization: Bearer p0k_..., buy at https://x402-bazaar-rank.x402-bazaar-rank-worker.workers.dev/keys/buy?usd=5) the tool pays the call itself, returns the data and deducts the price. First call each day returns the data itself, free; later calls return the paid request.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "name": "<name>"
    },
    "name": "check_counterparty"
  }
}

Input Schema

Name	Required	Description
`lei`	No	Optional 20-character LEI: read instead of a name search
`name`	Yes	Counterparty name in Latin letters
`address`	No	Optional crypto wallet address to screen too
`country`	No	Optional ISO country, e.g. DE (non-US skips the FDIC section)

Schema Changelog

Changes observed during successful MCP inspections.

First observedNov 7, 2026

TDQS

A4.4/5.0

Behavior5/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already declare this a safe, read-only, idempotent operation, and the description adds substantial non-obvious behavior: $0.015 per call, an x402/MPP payment handshake, invalid input refused before any charge, an optional Bearer access key that auto-pays and deducts, and the first call each day being free with subsequent calls returning the paid request. That is exactly the kind of context annotations cannot express.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The core use case is front-loaded, but the body is a run-on sequence mixing payment mechanics, a long key-purchase URL, and a dangling fragment ('A name, optionally with country, LEI or wallet address') whose placement is confusing. Several clauses could be tightened or reordered without losing information.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

For a billed, single-call screening tool with no output schema, it covers the payment path, authentication options, cost, free-tier behavior, and input validation failure. The only gap is what the returned screening payload contains beyond the named lists, which an agent must discover on the first call.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so all four parameters are already documented in the schema, including the LEI-instead-of-name and non-US country/FDIC notes. The description mostly restates the parameter set ('A name, optionally with country, LEI or wallet address'), with only the UK/Canada organisation-and-wallet restriction adding marginally new meaning; baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a concrete verb and resource ('screens a name ... against OFAC SDN, UK, EU, Canada and US CSL') and pins the endpoint (GET /check/counterparty). It is immediately distinguishable from siblings like sanctions_screening and check_payee, which it names explicitly.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

It opens with an explicit when-to-use trigger ('vet a counterparty before paying or onboarding it') and routes elsewhere with conditions: 'for one payee address before paying use check_payee; for a plain list lookup of an address or name use sanctions_screening'. Coverage limitations (UK and Canada: organisations and wallets only) are also flagged.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

All P0: sanctions, KYB and payee checks tools Inspect

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