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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so safety is covered. The description adds genuinely non-derivable behavioral context: the three match outcomes, that 'unknown' means never checked rather than absent, that the record is dated evidence rather than a safety rating, and that the call is free. Rate limits or latency characteristics are not mentioned.

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 tight sentences: the action and precondition come first, the possible outcomes second, and the interpretive caveat plus cost/read-only note last. Every sentence carries information an agent needs and none 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?

For a single-parameter read tool with an output schema and full annotation coverage, the description supplies the missing interpretive layer — what each match value means and how to read an 'unknown'. Nothing required to call it correctly or interpret it is absent.

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?

With one parameter at 100% schema description coverage, the schema already documents that the URL should be passed as held, including any query string. The description adds no syntax, normalization, or format guidance 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 ('check an endpoint URL') and scopes it precisely to a URL the caller already holds, which implicitly separates it from the discovery-oriented siblings like find_paid_service. It stops short of naming any sibling or the alternative to use instead, so differentiation requires inference rather than being explicit.

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?

'Check an endpoint URL you already hold before paying it' gives a clear triggering context (pre-payment verification of a known URL), and the explanation of 'unknown'/'delisted' clarifies what the result means. No exclusions or named alternatives are given, so the agent must infer when to prefer find_paid_service or get_service_details instead.

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