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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), yet the description still adds real context: the data comes from a curated statutory table with moved holidays applied, a free demo has a daily quota, and production volume goes through GET /cl/feriados via x402. That quota/access-model detail is not derivable from annotations and directly affects how an agent should call it at scale.

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?

Three tight sentences: what it returns and its scope first, the sibling routing second, access/rate constraints last. No filler, and the most decision-relevant information is front-loaded.

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 single-optional-parameter read tool with no output schema, the description covers source of truth, year scope, moved-holiday handling, and access model. It stops short of describing the returned record shape (e.g. date, name, type), which is the only remaining gap for an agent planning to consume the output.

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?

With one parameter at 100% schema coverage, the schema already documents 'ano' as year 2026 or 2027 with the current year as default. The description restates the same year range but adds no extra semantics such as accepted formats or behavior for out-of-range years.

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 (list), resource (Chile's official national holidays), scope (2026 or 2027, national, statutory, moved holidays included). It also names the sibling it supersedes, so an agent can distinguish it from days_holidays without opening either schema.

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?

Explicitly instructs 'Prefer it over days_holidays for Chile', giving both the alternative and the condition that selects it. It does not say what to do for years outside 2026/2027 or what days_holidays remains good for, so the routing guidance is clear but not exhaustive.

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