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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), yet the description still adds real value: a rate limit, silent truncation to the top 3 results on the free tier, a ranking methodology, and an escape hatch to the paid /v1/find route. The only gap is it doesn't say what happens when the quota is exhausted or how aggressively results are truncated.

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?

Two dense sentences with the action front-loaded, followed by ranking criteria, output contents, and quota terms. Every clause carries information, though the second sentence stacks ranking factors, outputs, and pricing into one long list that could be split for faster scanning.

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 3-parameter, read-only discovery tool with full schema coverage, annotations, and an output schema, the description covers purpose, ranking logic, output contents, quota limits, and a paid alternative. Nothing essential is missing, short of explicit sibling routing or quota-exhaustion behavior.

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 description coverage is 100% and each of the three parameters already carries a description and example, so the baseline of 3 applies. The description reinforces 'need' as plain-language intent and mentions price and network as outputs, but adds no filtering semantics beyond the schema (e.g. whether maxPrice excludes or merely ranks endpoints).

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 states a specific verb and resource ('Find which live x402 paid API to call') and grounds it with concrete example needs ('transcribe audio', 'web search', 'token price'). It also explains the ranking basis (relevance plus measured seller reputation), which distinguishes it in spirit from reputation/leaderboard siblings, though it never names those siblings explicitly.

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?

Usage is implied by 'for a need', and it does disclose a concrete operational boundary (free: 10 calls/day per client, top 3 results; full results via paid HTTP /v1/find). However, it gives no explicit when-to-use-this-vs-sibling guidance, e.g. whether to call x402_seller_reputation or x402_readiness_check first to validate a candidate endpoint.

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