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

Beyond the readOnly/openWorld/idempotent annotations, the description discloses that this is a paid x402/USDC-on-Base tool at $0.001 per successful call and that an unpaid call returns a PaymentRequired object — critical cost and failure-mode context. It also scopes the data source ('public calendar data only') and explains the automatic year lookahead.

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?

It front-loads the use case and wastes no words, with payment terms last. The first sentence, however, crams both the usage trigger and the full return specification into one long clause, which slightly hurts 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?

There is no output schema, so the description must describe returns — and it does so fully (boolean, matching record(s), next holiday). Combined with annotations covering safety and the description covering cost and data scope, an agent has everything needed to call this correctly.

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?

With 2 parameters at 100% schema description coverage (date format YYYY-MM-DD, ISO 3166-1 alpha-2 for country), the schema already carries the parameter semantics. The description adds no extra constraints such as supported country coverage or behavior for invalid codes, 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?

The description gives a precise verb+resource (check whether a given country/date is a public holiday) and spells out the return payload: isHoliday true/false, matching holiday records, and the next holiday on or after that date. That combination of output shape cleanly separates it from siblings like holidays_list, holidays_next, and holidays_long_weekend without needing to name them.

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?

It states concrete usage contexts (before booking meetings, shipping deadlines, marketplace cut-offs) and the lookahead behavior when no holiday is near. However, it never says when NOT to use it or points to the sibling that lists holidays in bulk, so routing between holiday_check and holidays_next is left to inference.

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