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

Annotations only declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered elsewhere. The description adds genuinely useful behavior beyond that: the exact cost ($0.002 USDC), the x402 payment flow, and the fact that the call returns an HTTP request plus payment requirements rather than data directly. It does not cover rate limits or failure/refund behavior, keeping it out of 5 territory.

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?

Two sentences, front-loaded with the critical paid/x402 context before the data description. Efficient overall, though the payment mechanics and the data scope are interleaved rather than cleanly separated.

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 carries the burden of explaining returns, and it does explain the unusual x402 request/payment-requirement response. It stops short of describing the holiday payload shape or the is_holiday return format, but for a 3-parameter lookup tool it is largely complete.

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 only 33%, so the description must compensate. It adds the date format (YYYY-MM-DD), the country scope (~490 countries/territories), and the year range, but the date parameter's effect is described only obliquely and the country ISO2 meaning is left to the schema. Partial compensation for the coverage gap.

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 specific verb+resource: public holidays for ~490 countries/territories for 2026 and 2027, with an optional date lookup that answers is_holiday. This is far more concrete than the bare name 'holidays'. However, it makes no attempt to distinguish itself from the closest siblings (country, currency), so it stops short of a 5.

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?

Usage is only implied: 'optional date=YYYY-MM-DD answers is_holiday' tells the agent what the date parameter buys you, and the year enum implies year-scoped lookups. There is no explicit statement of when to reach for this tool versus alternatives, nor any prerequisites beyond the payment note.

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