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

Annotations already declare readOnly/idempotent/non-destructive, and the description still adds real behavioral context: it is free and spends nothing, it returns the listing regardless of verification status and reports payment_verified honestly, and it explains that reliability is a running score that is not a guarantee. That pre-empts exactly the misinterpretations an agent would otherwise make from the field names.

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?

Purpose is front-loaded, but the middle is repetitive: 'not the per-call price', 'not the price', and 'The per-call price is price_min and price_max' make the same disambiguation three times. The reliability explanation is long for what it delivers, and the docs URL trails at the end where it is least useful.

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 properly carries the return-value burden, covering verification fields, pricing fields, and the reliability object's score/band/computed_at. It stops short of describing not-found or error behavior, which is the main remaining gap for a single-record lookup.

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?

Single parameter with 100% schema description coverage, so the schema already carries the meaning of 'id'. The description's 'by its id or slug' restates the schema rather than adding format or lookup semantics, which is the expected baseline when the schema does the work.

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: fetch a single live listing by id or slug, with an enumeration of what comes back (base_url, price range, network, verification state). 'Single' implicitly contrasts with the list/search siblings, but no sibling is named so the differentiation is left to inference.

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?

Usage is only implied – you call this when you already have an id or slug, and the schema note points at search_apis/list_apis as the id source. There is no explicit when-to-use / when-not statement, and no guidance on what to do when the id is unknown or the listing is absent.

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