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 real value beyond that by disclosing which fields come back and that some are conditional ('si renseigné', 'si indiqué'), plus that the base XOF price is always included alongside the requested currency. It omits failure behavior for an invalid id/url.

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?

Two compact sentences, front-loaded with what the fiche contains followed by the accepted identifiers. Dense but every clause adds information; only minor tightening is possible.

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 sensibly enumerates the returned fields so the agent knows what a call yields. It is nearly self-sufficient, missing only edge-case handling (no identifier supplied, conflicting identifiers, unknown book).

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%, so the schema already explains id, url, site, slug and currency in detail. The description only restates that id/slug/url are acceptable identifiers and gives no extra constraint (e.g. precedence when several are supplied), so the baseline 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 (fetch the full record of one book from eglise.shop) and enumerates the returned fields (résumé, description, auteurs, ISBN, éditeur, prix, lien). It also implicitly separates itself from search_books by noting the id is 'renvoyé par search_books', so an agent can pick the right tool without opening schemas.

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?

Tells the agent which inputs to supply (id from search_books, or slug, or product URL), which is a clear usage path. It does not explicitly say 'use search_books first to discover the id' nor when not to use this tool, so it stops short of full when/when-not guidance.

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