É feriado?

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

With no annotations provided, the description carries the burden of disclosing behavior. It states the tool 'indicates' whether a date is a holiday, which implies a boolean response. It does not detail error handling for invalid dates or the exact output format, but for a simple predicate tool the core behavior is fairly transparent. The description is not misleading and provides enough to form a mental model.

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 a single, scannable sentence in Portuguese that conveys all essential information. There is no redundancy or filler, and it front-loads the core purpose. Every word earns its place, making it appropriately sized for a simple query tool.

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?

Given the low complexity (one parameter, no output schema, no annotations), the description is nearly sufficient. It explains the scope (national holiday in Portugal) and the parameter format. However, it does not explicitly state the return type (e.g., boolean) or behavior for invalid dates, which would be helpful given no output schema exists. Still, the simplicity of the tool means the description is close to complete.

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 schema has 100% description coverage for the single 'date' parameter, including its format (YYYY-MM-DD) and pattern. The description repeats the format in parentheses but adds no additional meaning beyond what the schema already provides. This aligns with the baseline of 3 for high schema coverage, as the parameter semantics are fully handled by 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?

The description clearly states the tool's function: 'Indicates whether a date (YYYY-MM-DD) is a national holiday in Portugal.' It uses a specific verb ('indicates'), specifies the resource (a date), and scopes it to Portugal. This distinguishes it from the sibling validation tools (validate_nif, validate_iban, validate_postal_code) and list_holidays, which either validate identifiers or list holidays rather than checking a specific date.

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 implies the tool is for checking a single date's holiday status, providing clear context for when to use it. However, it does not explicitly compare itself to list_holidays or say when not to use it, though the distinction is fairly obvious. Since there are no explicit exclusions or alternatives mentioned, it falls short of a 5 but is clear enough for a 4.

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