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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so the safety profile is covered. The description adds value beyond that: per-call cost, supported coverage (250 countries/regions), and a concrete output shape. It still omits what happens on invalid subdiv/language combinations or unknown country codes.

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 fragments: what it returns, what it costs, and the exact response shape. Front-loaded with the highest-value information and no filler whatsoever. The inline JSON sketch communicates return structure in minimal characters.

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?

With no output schema, the description usefully inlines the response shape ({country, year, subdiv, holidays[], count}), and cost is disclosed. Combined with rich schema descriptions and full annotation coverage, an agent has almost everything needed. Only minor gaps remain around error behavior and variable subdivision support across countries.

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 83%, so the schema already documents all six parameters including formats and defaults. The description only echoes parameter names (year, subdiv, language, category) without adding syntax or constraint detail. This meets the baseline rather than exceeding it.

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 resource (public holidays), scope (about 250 countries and regions), and key qualifier (for a given year, with optional subdivision/language/category). No sibling tool overlaps with holiday data, so the agent can identify this unambiguously. The verb is carried by the name ('lookup'), making the intent unmistakable.

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?

Usage is implied rather than stated — the description never says when to call this instead of anything else, though no sibling offers comparable data. It does add a decision-relevant cost signal ('1 credit per call'), which helps an agent weigh the call. No exclusions, prerequisites, or edge-case conditions (e.g., subdiv support varies by country) are given.

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