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

Annotations already declare readOnlyHint=true and idempotentHint=true. The description adds the exact return structure (date, name, name_en), the fixed count of 9 holidays, and the boundary that only national holidays are included, significantly enriching behavioral context beyond the annotations.

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 well-structured and every sentence earns its place: it states the action, lists the return fields, specifies the count, explains the use case, and clarifies the exclusion of regional holidays. No redundancy or fluff.

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 simple one-parameter tool without an output schema, the description compensates fully by specifying the return structure, the fixed number of holidays, the intended use cases, and the limitations. It is complete for an agent to select and invoke the tool correctly.

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 single parameter 'year' is fully described in the schema with format and example (100% coverage). The description only refers to 'a given year' without adding new details, so the baseline of 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 uses the specific verb 'Returns' and identifies the resource 'Spanish national public holidays' for a given year. It also lists the return fields (date, name, name_en) and distinguishes itself from regional holidays and sibling country-specific tools (France, Portugal), making the purpose highly clear.

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 description explicitly states 'Use when calculating business deadlines, delivery dates, or scheduling tasks that must avoid non-working days in Spain' and notes the exclusion of regional holidays, providing clear context. However, it does not name an alternative tool for regional holidays, so it falls short of a full 5.

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