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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds useful context (data source is comontel.fr, subscription-status is included), but nothing about caching, freshness, or failure behavior for an id it may not resolve.

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?

One compact paragraph, front-loaded with the payload contents before the usage rule and the parameter. Every clause carries information; only the parameter restatement is mildly redundant with the schema.

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 an output schema present, return-value detail is not required, and the description supplies purpose, trigger, parameter, and data source. It is complete enough for a single-parameter lookup, though it does not address behavior for an invalid/unknown plan_id.

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% and plan_id already carries an enum with a description, so the schema does the heavy lifting. The description merely repeats the same three values ('essentiel, pro, business') without adding format or semantics beyond the schema.

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 resource ('fiche complète d'un forfait') and enumerates the scope of detail it returns (prix HT/TTC, Go France/Europe, 5G, appels/SMS, page officielle). It implicitly separates itself from list/compare siblings by requiring a specific plan, though it never names get_plans or compare_plans directly.

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 an explicit trigger condition: 'À utiliser quand l’utilisateur cite un forfait précis.' That is clear when-to-use guidance, but no alternative tool is named for the opposite case (e.g. browsing all plans), so the routing is only half specified.

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