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

Annotations already cover read-only/idempotent/closed-world, but the description adds context beyond them: results are cached, the caller's URL is never fetched, the endpoint is never paid, unlisted/unavailable/stale data is not charged, unknown means missing evidence, and repeated paid calls may incur another charge. Pricing ($0.005 with a shared free trial) is disclosed, which no structured field provides.

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?

Front-loaded with what is returned, then behavior, parameters, routing, and price. Almost every sentence carries distinct information, though the cost statements ('Price $0.005 per cached lookup' and 'repeated paid calls may incur another charge') are close enough to feel slightly redundant.

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?

An output schema exists, so return shape needn't be explained, and the description still covers the semantics an agent needs: caching, scoring/unknown meaning, billing behavior, listing prerequisite, and the sibling routing decision. Nothing material is left to inference for this two-parameter, read-only 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 100%, so the baseline is 3. The description goes slightly beyond the schema by emphasizing the URL must be the exact resource URL and by giving a practical rule for method ('add method when the URL has multiple advertised methods'), which adds conditional intent even though it overlaps the schema's 'required if the URL is ambiguous' wording.

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 (returns cached observations) and resource (an x402 endpoint URL) plus the artifact returned (transparent score, components, seven-day probe history). It also explicitly carves out what it is not ('not a paid-delivery or compliance guarantee') and names sibling tools, so an agent can distinguish it from check_payee and preflight_payment without opening any 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 explicit when-to-use ('for endpoint history and price context before paying') and routes two named alternatives with their own conditions: check_payee for wallet/name screening, preflight_payment for an allow/hold/block decision. It also states the precondition that the URL must already be publicly listed by Bazaar or x402scan.

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