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

Annotations already declare readOnly, idempotent, non-destructive and open-world, and the description adds genuinely new operational context: one credit is spent per request (failed requests included) and the Public Holidays API key is required. Cost and auth requirements are exactly the details annotations cannot convey.

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 sentences, front-loaded with the resource and granularity, followed by the plan constraint and cost/auth note. The bare fragment 'Public Holidays API' is redundant padding against the tool name and title, but nothing else is wasted.

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 still identifies what is returned (holidays of a type, for a scope) well enough to call the tool. It covers scoping, plan constraints, cost and credentials; only the response shape is left implicit, which is a minor gap.

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 the baseline is 3, but the description adds semantics the schema lacks: the free-plan requirement that year/month/day be supplied together and the paid-plan rule that omitted values default to today. That is meaningful behavior beyond the per-field descriptions.

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 — returns public, local and religious holidays for a country at day, month or year granularity — and the granularity is spelled out. Siblings are all in unrelated domains (VAT, currency, IP), so there is no ambiguity to resolve, but the scope is nonetheless precise.

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 plan-dependent usage rules: free Abstract plans require year, month and day together, while paid plans default missing values to today. It does not name exclusions or alternatives, but no sibling overlaps this resource, so the practical when-to-use condition is covered.

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