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

Annotations already cover safety (readOnly, idempotent, non-destructive), so the description earns credit for adding real behavior: the fallback to newest catalogue items when no id is given, the fact the XOF base price is always returned alongside the requested currency, and that the link carries the currency to the site. It omits error behavior for an invalid id, but the added operational context is substantial.

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?

Front-loaded with what is returned, then the input options in a single compact sentence. Dense parenthetical asides make it slightly harder to scan, but no sentence 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?

With five optional parameters and no output schema, the description does the necessary work by listing the returned fields and the currency rule. The remaining gap — identifier precedence and behavior on a nonexistent id/slug — is minor for a read-only 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?

Schema coverage is already 100%, and the description still adds meaning: it explains that id comes from search_books and that omitting all identifiers changes the result set entirely. The url/site relationship is only echoed from the schema, so it is not a full 5.

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?

The description states a specific verb and resource ('Fiche complète d'un livre') and enumerates exactly what the record contains (résumé, auteurs, ISBN, éditeur, prix, lien). It also names search_books as the source of the id, so an agent can separate this detail-fetch tool from the search sibling without opening a 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?

It gives concrete invocation paths — id from search_books, or slug, or product URL — and even describes the degenerate case where no identifier yields the catalogue's latest releases. What it lacks is an explicit ordering/precedence when several identifiers are supplied, and it never says when to prefer this over search_books in so many words.

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