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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description still adds real behavioral content beyond them: the result is a compatibility list with no 'best' designation and includes non-matching plans with a stated reason, so the agent knows to expect two buckets in the response.

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?

Three compact sentences, front-loaded with the operation and its scope, then the domain rule, then the routing rule. Only mild redundancy from restating the Switzerland/Europe envelope rule already present in 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 values need not be described, and annotations plus full schema coverage carry the structured burden. The description supplies the missing business logic (shared CH/EU allowance, no ranking, rejection reasons), leaving little an agent needs that isn't available somewhere.

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 every one of the 7 parameters is documented in the schema, so the baseline is 3. The description's most valuable addition — that Switzerland and Europe share a single allowance distinct from France — is already asserted in the europe_data_gb schema description, so it largely restates rather than extends 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?

States a specific verb and resource (returns Flytel plans compatible with a stated need) and enumerates the dimensions considered: GB/month in France, Switzerland, Europe; calls to/from Switzerland; eSIM. It also explicitly marks the boundary of its own scope (it does not rank one plan as best), which separates it from a ranking-style tool like compare_plans.

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?

Gives an explicit routing rule: use this when the needs are quantified, otherwise use flytel_conseil_forfait. Naming a sibling and the condition that selects it is exactly the guidance an agent needs; it also effectively states when NOT to use it.

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