Spend Check (paid, credits or x402)

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

Annotations already mark readOnly and idempotent, but the description adds valuable behavioral context: cost per check, latency, the policy that 'An unknown payee is always caution, never clear,' and a detailed output structure. This goes well beyond annotations without contradicting them.

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

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

The description uses labeled sections (WHAT, WHEN, WHEN NOT, COST, LATENCY, OUTPUT) that are concise and front-loaded. Each sentence adds useful information without redundancy or wasted words.

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

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

The tool has an output schema, but the description still provides a helpful preview of return fields. It also covers cost, latency, usage boundaries, and a key policy caveat. The inclusion of sibling tool references and cost information makes it operationally complete for an agent.

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

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

Schema coverage is 100%—both payTo and amount_usd are well-described. The description adds some contextual framing (e.g., 'pre-payment' and 'raising a payment limit') but does not introduce parameter-specific meaning beyond the schema. This aligns with the baseline for high schema coverage.

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

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

The description clearly states a specific verb+resource: 'pre-payment counterparty check. Given a 0x address or URL, returns a clear/caution/avoid verdict with per-source evidence... and a signed attestation.' It distinguishes from siblings by explicitly pointing to oracle_verify_work for judging delivered work.

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

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

Explicit WHEN clauses: 'before sending any x402 payment to a service you have not paid before, or before raising a payment limit.' WHEN NOT is also explicit: 'for services you already trust, for judging delivered work (use oracle_verify_work), or as a guarantee.' This provides clear alternatives and exclusions.

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