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

Goes well beyond the readOnlyHint/openWorldHint annotations: it discloses the 60 calls/minute rate limit, no-auth requirement, the 36 h staleness window, the 7-day TERMS_MAX_AGE_HOURS rule that downgrades pay to recheck (reason_code terms_stale), and the exact fields returned per result.

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?

Purpose and scope are front-loaded in the first clause, followed by return shape, filtering, freshness rules, and a workflow pointer. Dense but every sentence carries information; only the parenthetical acronym (TERMS_MAX_AGE_HOURS) is slightly over-packed.

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?

There is no output schema, so the description supplies the return contract itself — price, network, last_checked, stale, verdict with reason, and receipt. Combined with rate limits, auth posture, and the recommended follow-up call, an agent has everything needed to invoke and interpret this tool.

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 67%, and the description compensates: it explains that q matches words against URL or source list, that limit caps results at 20, and that verdict filters the freshness-adjusted verdict (a non-obvious detail the schema's bare enum omits).

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 resource — discovery of x402 pay-per-call endpoints — plus its source (402xAgent's weekly crawl) and result cap (up to 20). It also names endpoint_spot_check as the pre-payment companion, which separates it from sibling tools such as search_catalog or lookup.

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?

Gives clear operating guidance: skips are included by default unless verdict filters them, and endpoint_spot_check should be run right before paying with quote=<receipt_id>. It doesn't explicitly say when to prefer it over search_catalog or lookup, so it's short of full alternative routing.

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