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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered. The description adds the result character (a field-by-field diff with per-plan values plus identical fields), but since an output schema exists this is largely redundant, and it says nothing about behavior with unknown or duplicate IDs.

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?

A single front-loaded sentence that states the action, the cardinality constraint and the return structure with zero filler. Nothing could be removed without losing information.

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?

For a one-parameter, read-only comparison tool with rich annotations and an output schema, the description is nearly sufficient: it conveys scope and result shape. It stops short of explaining error behavior or the relationship to the other plan-oriented siblings, which is the only real gap.

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?

The description's 'deux à cinq' mirrors the schema's minItems=2/maxItems=5, reinforcing the cardinality rule. The schema itself already documents plan_ids with an example and a pointer to list_plans, so the description adds little semantic detail beyond the count constraint; a baseline 3 is appropriate.

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 (compare) and resource (forfaits Flytel) plus the scope (two to five) and the shape of the result (what differs, value per plan, what is identical). It is clear and unambiguous, but it never names or contrasts with the closest siblings (get_plan, list_plans, find_best_plan), so the differentiation is left to inference.

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?

The 'deux à cinq forfaits' boundary implies the usage context and rules out one- or many-plan cases, which is useful. However, there is no statement of when to choose this over find_best_plan or check_usage_compatibility, and no prerequisites (e.g. that valid IDs come from list_plans).

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