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

Annotations already declare read-only, non-destructive and open-world; the description adds genuinely new context: data provenance (own statutory rules for 8 countries vs Nager.Date elsewhere), the 2024-2100 validity window, and per-call pricing with 25 free calls and free failures. It also explains why repeat calls aren't free, which reconciles with idempotentHint=false, but does not discuss error behavior or coverage limits outside the 8 statutory countries.

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?

Front-loads what the tool returns and who it is for, then data sources, then pricing. Dense but nearly every clause carries information; the pricing/key sentence is long but justified for a paid endpoint.

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 lists the returned fields and their meaning (observed-day shifting, nationwide flag), which is what an agent needs. Remaining gaps are the year-range applicability for non-statutory countries and result format (array vs object), neither of which blocks correct invocation.

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%, with both parameters fully documented (ISO code or English name, year 2024-2100 defaulting to this year). The description only adds exemplar codes (SE, JP, CA) and a sample call, so it does not materially deepen semantics beyond the schema.

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+resource ('Public holidays for a year in over 100 countries') and enumerates the returned fields (date, local and English name, nationwide flag, observed day), so it is unmistakable against siblings like weather, time or country.

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 a clear use context ('scheduling, delivery dates and business-day maths') plus a concrete call example (country=SE), but offers no explicit when-not guidance or named alternative — acceptable here since no sibling covers holidays.

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