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

With no annotations supplied, the description carries the full behavioral burden and does so: it discloses the ranking signal (30-day unique payers, repeat calls per payer, scanner traffic filtered), data freshness (re-crawled every 6 h), billing ($0.008 USDC per call via x402 on Base), and failure semantics (no match = 404, not charged). These are exactly the mutation/cost/auth traits an agent cannot get from structured fields.

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?

Four short clauses, each front-loaded with a distinct fact: what it searches, how results are ranked, what happens on no match, and what it costs. No filler and no repetition of the schema or tool name.

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?

For a three-parameter search with no output schema and no annotations, the definition covers purpose, result contents (sellers plus price plus cheapest proven alternative), cost and error behavior. It could still be clearer about response shape/ordering guarantees and how large result sets are paged beyond 'limit', which keeps it off a 5.

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%, so 'q', 'limit' and 'minPayers' are already documented, and the baseline is 3. The description adds only indirect meaning by tying 'minPayers' to the demand-ranking concept ('30-day unique payers'); it gives no syntax hints for query phrasing or limit defaults beyond what the schema says.

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?

States a specific verb and object ('find paid APIs for any task') plus a precise scope ('the whole CDP Bazaar, 110k+ endpoints, re-crawled every 6 h'), so the resource is unmistakable. It stops short of naming the near-neighbours in the sibling list (x402check_check, list_services, intel_do_search), which is the one thing keeping it from a 5.

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?

'Find paid APIs for any task' implies the use case, and the 404/not-charged rule tells the agent what happens on a miss. However, there is no explicit when-not guidance or pointer to an alternative such as x402check_check for validating a specific endpoint, so routing between similar tools is left to inference.

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