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

Annotations already declare readOnly, idempotent, openWorld and non-destructive, so safety is covered. The description adds real behavioral context beyond that: it fans out to three independent providers, returns agreement/disagreement rather than a single answer, and implicitly trades speed for accuracy.

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?

Two sentences, front-loaded with the decision trigger and followed by the mechanism. Every clause earns its place, though the dense list of use-case domains is slightly heavier than needed.

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 an output schema present, return-shape detail is unnecessary, and annotations cover the safety profile. The description supplies the when, the what, and the cross-provider model; only the explicit sibling reference is missing for full completeness.

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 100% (year range 1975-2075, ISO alpha-2 country code), so the schema fully documents both parameters. The description only restates 'a country and year' at a high level and adds no format or edge-case detail, making 3 the correct baseline.

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 (compares the national holiday list for a country and year across three independent providers) and explicitly distinguishes itself from the pick-one-source behavior implied by list_public_holidays. An agent can tell what this tool returns without opening a 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?

Gives concrete when-to-use triggers: accuracy over speed, user disputes a date, contracts/payroll/settlement/compliance deadlines. The contrast 'rather than picking one' implies the single-source alternative, but the sibling list_public_holidays is never named, so the routing is inferable rather than explicit.

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