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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld=false). The description adds two behavioral details beyond them: the data source URL and the fact that an 'inconnu' status is returned when a destination is not listed, which meaningfully complements openWorldHint=false. Return values needn't be explained since an output schema exists.

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 description is front-loaded with purpose, then the returned fields, usage cue, edge case, and source — a logical order with little waste. The 'Paramètres : plan_id et destination' line is redundant given full schema coverage, a minor deduction.

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 100% schema coverage, rich annotations, and an output schema present, the description only needs to add framing — which it does by scoping the domain, disclosing the unknown-status edge case, and citing the source. It is essentially complete, lacking only explicit sibling routing.

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 documents both plan_id (with enum) and destination (with format examples). The description only restates 'Paramètres : plan_id et destination' without adding format or constraint meaning, 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?

The description names the specific resource and its scope: what a plan (forfait) permits in a given destination, enumerating the exact dimensions returned (inclusion, usable Go, calls/SMS on site, calls from France, applicable rule). This is clearly distinguishable from generic siblings like get_plan or get_country_info, though it never names an alternative. The verb is implicit ('get') rather than stated, keeping it just below a 5.

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 one usage cue — 'À utiliser pour les voyages et les frontaliers' — which tells the agent the domain (travel and cross-border users). However, no when-not-to-use condition or named alternative sibling (e.g., get_country_info for general country facts, get_plan for plan details) is offered, leaving selection guidance implied rather than explicit.

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