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 earns credit by adding cost and auth behavior beyond the annotations: 'FREE with any API key,' 'Unmetered: never counts against the key's allowance,' and the alternative X-API-Key header path. It does not describe rate limiting or response shape, but those gaps are minor against the quota/auth disclosure.

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 short sentences with no filler. Slight weakness in front-loading: it opens with billing/promo content and a free-key URL rather than stating the core capability, and the actual function is only defined by reference to a sibling ('Same as get_public_holidays').

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?

An output schema exists, so return values need no explanation, and annotations cover the safety profile; between schema and description, params and auth are fully covered. The only unaddressed phrase is the unexplained 'seven brands,' which slightly limits how confidently an agent can predict coverage.

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 description coverage is 100%, so country, subdivision, and api_key are already documented in the schema with enum coverage. The description's auth note ('or send the key as the X-API-Key header') duplicates what the api_key schema description already says, adding no new parameter meaning. Baseline 3 is appropriate.

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 and resource (get public holidays) with explicit scope: 'every country across all seven brands, not only North American.' It directly anchors itself against the sibling get_public_holidays, so an agent can distinguish the two 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 names the alternative ('Same as get_public_holidays, but for every country... not only North American'), which tells the agent exactly when to pick this tool over its near-identical sibling. The workaround-free coverage claim ('not only North American') gives the exclusion condition implicitly but unambiguously.

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