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

Annotations cover the safety profile (readOnly, non-destructive, openWorld), and the description adds high-value behavior beyond them: a $0.003 USDC per-call price, the x402 in-band payment mechanism, supported chains (Base, Solana, Polygon, Arbitrum), which clients auto-pay, and a free sample call. This is exactly the kind of non-schema context an agent needs before invoking a paid tool.

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-loaded with purpose, then a compact parameter recap, then pricing and a sample. The parameter list partly duplicates the schema, and the payment sentence is slightly verbose, but nothing is wasted given a paid API needs disclosure.

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?

For a six-parameter paid tool with no output schema, the description covers purpose, params, payment, and example invocation. It stops short of describing the return shape (e.g., whether a date check returns a boolean and what fields each holiday carries), which is the only notable gap.

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 67%, and the description compensates by enumerating all six parameters with concrete examples (DE/US/CH/JP, BY/CA/ZH), the ISO 3166-1 alpha-2 convention, the YYYY-MM-DD format, and defaults for year and include_observances. It adds meaning over the bare schema for the fields lacking descriptions (year, include_observances).

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 and bank holidays for 200+ countries and their regions') with scope (any year, with local names) and a secondary mode ('check whether a given date is a holiday'). No sibling in the list overlaps, so the tool is unambiguously identifiable.

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?

Clearly frames the two usage modes (list holidays vs. date check) and gives defaults (year = current, include_observances = false), plus a free-sample invocation. There are no sibling alternatives to disambiguate against, so it lacks explicit when-not guidance, but the context is clear.

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