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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds useful behavioral detail: the verdict enum (avoid/caution/ok/unknown) and the evidence returned. It doesn't say what happens on unresolvable URLs or how to interpret 'unknown.'

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?

One sentence, front-loaded with the invocation triggers before the return details. Dense but no filler; the return-value clause is slightly redundant given the output schema exists.

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 read-only, one-parameter tool with a full output schema, the definition covers triggers and the shape of the verdict. The only gap is guidance on handling 'unknown' or unresolvable inputs.

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% and the single param is fully documented in the schema (URL or bare domain). The description only hints at the URL concept through the 'names an API' phrasing and adds no format or syntax detail beyond the schema.

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: 'Check an x402 seller.' The scope is unmistakable, though it doesn't name the sibling tools (list_reliable_sellers, recent_changes) to differentiate 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?

Gives explicit triggers: before any x402 payment, before retrying after an HTTP 402, or when the user names an API they intend to pay per call. It doesn't say when NOT to use it or name a specific alternative to use instead.

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