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

Goes well beyond the readOnlyHint/openWorldHint annotations: discloses pricing (0.002 USDC per successful call via x402), failure semantics (HTTP 400 before payment, no charge), which dates are approximate (moon-dependent dates flagged as estimated), and what fields come back (English and local names, weekend days). That is exactly the kind of paid-external-API context an agent cannot infer from annotations.

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?

A single dense paragraph with the use trigger front-loaded and no filler sentences; coverage, pricing, and error behavior each earn their place. It is packed tightly enough that the cost/error clauses blend into the data description, slightly hurting scannability.

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 characterizes the return payload (names in two languages, weekend days, estimated flags), plus pricing and error behavior. Nothing material for correct invocation of a paid, open-world lookup is missing.

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. The description restates the year range and region option already documented in the schema and adds no syntax or format detail beyond it, so it does not meaningfully deepen parameter understanding.

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 and scope: 'all public holidays of a country for a year', with coverage limits (247 countries, 2026-2028) and the regional variant. An agent can distinguish this from business_day/trading_day siblings by resource, though the mention of 'weekend days of the country' edges toward sibling territory without explicitly naming the alternative.

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?

Opens with an explicit trigger ('Use when an agent needs...') and enumerates concrete scenarios: planning deliveries, payments, deadlines, staffing. It lacks any when-not guidance or named alternative for business-day calculations, which would be the natural complement given the sibling set.

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