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

Annotations only cover the safety profile (readOnly, idempotent, non-destructive); the description goes well beyond them with interpretation-critical semantics: zero attempts means unknown rather than 0% success, and reported success is not a guarantee for the caller's runtime, payment method, or region. This is exactly the context an agent cannot derive 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?

Three short sentences, zero filler, and the most important caveat (zero attempts = unknown) is placed early where it will be read before the returned number is interpreted.

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 carries the burden of explaining returns; it names the key dimensions (sample size, recency, success rate) but does not enumerate the response fields or size/recency thresholds, leaving the agent to inspect the payload.

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% for the single parameter, and the schema already explains that a domain or HTTPS URL is accepted while paths are not identities. The description adds no syntax or format detail beyond that, so the baseline of 3 applies.

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: 'Look up a domain and its aggregate agent purchase attempt evidence.' The scope (single domain, aggregate evidence) is clear. It does not, however, explicitly differentiate itself from the sibling search_merchants, which is the most likely source of confusion.

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?

The description implies usage through its interpretive instructions ('Check sample size and recency'), and the title supplies the 'before checkout' context, but it never states when to call this versus search_merchants or submit_review. Usage is inferable rather than stated.

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