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

Annotations already cover safety (readOnly, idempotent, openWorld, non-destructive), and the description goes well beyond them: 422 error semantics with no charge, sub-0.1s latency, USD 0.001 price, a 10-calls-per-IP-per-UTC-day free tier, and an important accuracy caveat that data comes from python-holidays rules rather than an official calendar.

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 the purpose, then routing, error behavior, cost/latency, caveat and docs link in a logical order. Every sentence carries distinct information, though the pricing/latency/free-tier block makes it denser than strictly necessary.

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 values need no explanation. The description covers the remaining gaps an agent would care about: the alternative tool, error behavior, cost, rate limits, and the reliability caveat for legal/payroll use.

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 schema already documents year, country, language and subdivision. The description only references these parameters collectively via the 422 message and adds no syntax or format detail beyond the schema, so baseline 3 applies.

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 (public holidays of a country for a year), and the title reinforces it. It explicitly names the sibling it is not for ('To count working days use count_or_add_business_days'), so an agent can separate it from count_or_add_business_days without opening either 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 an explicit alternative and the condition that selects it: counting working days routes to count_or_add_business_days. It also tells the agent what happens on bad input (422 naming supported values), so edge-case routing is covered.

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