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

Beyond the readOnly/openWorld/idempotent annotations, it discloses the data provenance, the returned field set (date, names, global vs county-limited, fixed vs movable, holiday types), and crucially the payment model: x402 USDC on Base at $0.001 per successful call, with an unpaid call returning a PaymentRequired object. This is high-value operational context an agent cannot get 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?

Front-loads the purpose and use cases, then the return shape, then the payment terms. Dense and information-rich with little waste, though the long enumerations make it feel heavier than 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 no output schema, the description compensates by enumerating the returned fields, and it covers the paid-call flow end to end. Nothing an agent needs to invoke it correctly or interpret a payment failure 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 coverage is 100%, so country and year are already documented with format and default. The description still adds concrete country-code examples (LT, US, DE, JP) and confirms the year scoping, which marginally enriches the parameter meaning 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 and resource: returns every public holiday for a country in a given year. It distinguishes itself from siblings like holiday_check, holidays_next, and holidays_countries by implying a full-year enumeration, and names the upstream source (Nager.Date, ~100 countries).

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 concrete use cases (scheduling, payroll calendars, travel planning, 'is the office closed?'), which clearly frames when to reach for it. However, it never explicitly contrasts with the sibling holiday tools (holiday_check, holidays_next, holidays_long_weekend), leaving the agent to infer the boundary.

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