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

Annotations already declare readOnly/idempotent/non-destructive, so the safety profile is covered. The description adds genuine behavioral context beyond them: the from-CH / to-CH / roaming distinction and the fact that the answer depends on where the phone physically is versus the destination number. It does not describe pagination or edge cases (e.g. no coverage), but the output schema carries the return shape.

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?

Purpose and the from/to/roaming framing are front-loaded, and the routing sentence to flytel_tarifs_pays closes it cleanly. It is slightly long and partially repeats the usage_type enum from the schema, which is wasted text.

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?

An output schema exists, so return values need no explanation, and all three required parameters plus the conditional destination_country are covered. For a filtered-lookup tool this is close to complete; only edge behavior (unsupported combinations) is left implicit.

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 coverage is 75%, and the description meaningfully disambiguates the two country parameters — country_of_use is where the phone is, destination_country is the called party — a distinction the schema describes but the roaming framing sharpens. It also repeats the usage_type enum already in the schema, which adds nothing.

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: tells whether a given usage_type is included in a Flytel plan, scoped by country_of_use and destination_country. It explicitly distinguishes the three relevant cases (« depuis la Suisse », « vers la Suisse », itinérance), which an agent cannot infer from the name alone.

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 it for any « est-ce compris ? » question about calls, SMS or data — and names the sibling to use instead when the question is about out-of-plan pricing (flytel_tarifs_pays). When-to-use and the alternative are both stated.

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