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

With no annotations, the description carries the full burden and does disclose meaningful behavior: the default date is today in Lisbon, the default scope is national-only when municipality is omitted, and supplying a municipality adds its municipal (and regional, in Azores/Madeira) holidays. It does not cover invalid-input or error behavior, but the defaults are the key traits an agent needs.

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 sentence that front-loads the core action and packs format, default, and scope into compact parentheticals with zero waste.

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 two-param, zero-required tool with no output schema or annotations, the description covers defaults, formats, and scope behavior well. It could say a bit more about error handling for malformed dates, but nothing essential to selecting or invoking it is missing.

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 only 50% — 'after' has no schema description — but the description supplies its format (YYYY-MM-DD), its default (today in Lisbon), and its semantics (on or after). The municipality semantics live in the schema itself, so both parameters end up fully understood.

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 (Return) and resource (the first Portuguese public holiday on or after a date), and the 'first ... on or after' framing implicitly distinguishes it from the sibling list_holidays. It stops short of naming that sibling, so an agent must infer the division of labor.

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?

Conveys scope choices (whole country vs. one municipality) and the default date, which implies when the tool applies, but never explicitly states when to prefer it over list_holidays or what conditions select the municipality path beyond the field itself.

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