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

Annotations already declare readOnlyHint=true, so safety is covered. The description adds genuine context beyond that: the returned payload includes a citation, and lookups work "for every seller, a hidden test seller too," which signals id coverage. It does not say what happens with a malformed or unknown card_id, nor what a card actually contains, so it is additive but not rich.

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?

The whole definition is three dense sentences with no filler, and each clause (format, examples, provenance, coverage) carries information. Slightly front-loading the purpose before the ID grammar would improve scannability, but nothing is wasted.

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-only lookup with no output schema, the highest-risk failure mode is a wrong id format, and that is exhaustively covered. The gap is the return shape — "one card with its citation" does not enumerate card fields — but with no output schema the omission is minor at this complexity.

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?

Although the schema already documents card_id at 100% coverage, the description goes well beyond it: it spells out the three id grammars with concrete worked examples (offer:anthropic|claude-opus-4, model:anthropic/claude-opus-4, seller:anthropic) and states where valid ids originate. This is exactly the extra meaning the schema alone does not supply.

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?

"One card with its citation" states the resource and the return payload, and the surrounding ID-format text makes clear this is a single-item lookup keyed by card_id. It is distinguishable from search_offers (which produces the ids) and from the pricing siblings, though the phrasing is a noun fragment rather than an explicit verb+resource statement.

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?

It explicitly routes the agent: ids "come from search_offers (offer_id, model_id, provider_id) and from the card_url of every result," which tells the agent this is the follow-up call after a search. There is no explicit when-not guidance (e.g. don't use for bulk lookups, use search_offers instead), so it falls short of a 5.

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