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

Annotations already declare readOnlyHint and openWorldHint, but the description adds substantial context beyond them: no auth required, a 60 calls/minute rate limit, staleness rules (36 h = stale, a 7-day-old 'pay' downgraded to 'recheck'), and the default inclusion of skips. These are exactly the behavioral traits an agent needs before calling.

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?

Information-dense and front-loaded with what the tool returns, followed by filtering, freshness rules, and the safety caveat. Every clause carries meaning, though the long single paragraph could be broken up 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?

With no output schema, the description carries the full burden and does so: it enumerates returned fields (price, network, last_checked, stale flag, verdict with reason, receipt) plus rate limits and auth posture. Nothing an agent needs to call it correctly is missing.

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%, with q and verdict documented in the schema but limit only carrying default/min/max. The description compensates by stating the 'up to 20 endpoints' cap and clarifying that verdict filters on the freshness-adjusted verdict, adding nuance the enum alone does not convey.

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+resource ('discovery of x402 pay-per-call endpoints') and scopes it to '402xAgent's weekly crawl', which clearly differentiates it from siblings like search_catalog or lookup. An agent can tell what this returns without opening the schema.

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 operational context: skips are included by default, verdict filters them, and it explicitly routes the agent to endpoint_spot_check 'right before paying'. It does not, however, distinguish this tool from the other search-like siblings (search_catalog, lookup), so the alternative-selection guidance is incomplete.

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