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

Annotations already declare readOnly/idempotent/non-destructive/openWorld, so safety is covered. The description adds genuinely non-obvious behavior: the 400-day ceiling and, importantly, that a country without data returns an explicit error which must not be misrepresented as an empty holiday list. That error semantics is the kind of trait an agent cannot infer from structured fields.

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?

Two sentences, no filler. The resource enumeration is front-loaded and the critical error-handling caveat follows immediately, so the most important constraint is not buried.

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 no output schema, the description carries the burden of explaining returns, which it does by enumerating the three record kinds and their geographic limits. It omits any indication of response shape or ordering, but for a lookup tool with fully documented parameters and annotations, the definition is close to sufficient.

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 100%, so the baseline would be 3. The description goes beyond it by tying semantics across parameters: school holidays are often regional (hence region codes), traffic data is France-only, and the period is one country over at most 400 days. That cross-parameter framing adds meaning the schema does not.

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 exact resources returned (public holidays, regional school holidays with ISO 3166-2 region codes, and Bison Futé peak traffic days) plus the scoping constraint (one country, up to 400 days). No sibling tool covers holidays, so the resource enumeration alone is enough to separate it. An agent knows precisely what this returns.

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 clear operational context: single-country scope, 400-day maximum, and the rule to never report a country-level error as 'no holidays'. There are no comparable alternatives among the siblings, so no explicit routing is needed, but the description stops short of stating anything about when not to call it or how to choose among the kind values beyond the schema.

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