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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description is free to add the context that matters: the call is free of charge, it returns a stale/'last dated' verdict rather than a fresh check, unknown sites are non-errors, and how to obtain fresh data. That is meaningful behavior beyond what the structured fields convey.

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?

Four short sentences, front-loaded with the cost signal ('Free.') and the core semantics, then the error-expectation and the purchase route. Every sentence carries information an agent needs; nothing is padding.

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 must carry the return-value burden and it does: verdict, score, date, badge, and the known flag. Combined with the cost and freshness caveats, an agent has everything needed to call this correctly without probing.

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% and the single `url` parameter already documents the accepted https URL/hostname format. The description adds no further syntax, normalization, or edge-case detail for the input, 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+resource ('look up the last dated verdict for a website') and enumerates exactly what comes back: verdict, score, date, badge. It also differentiates itself from get_pricing by noting that a fresh check must be purchased there, so an agent can route 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?

Names the alternative tool explicitly ('To get a fresh check, buy one (see get_pricing)') along with the condition that selects it: this tool returns only previously cached verdicts. It further pre-empts a common misuse by stating an unknown site is a normal result (known: false), not an error.

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