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

Annotations only declare readOnlyHint and openWorldHint; the description adds substantive behavior beyond them: bad input returns HTTP 400 with no charge, and each successful call costs 0.002 USDC via x402. It also discloses data scope (247 countries, 2026-2028) and that weekends can be local (e.g. Fri-Sat), which affects results. It stops short of describing the response shape, so it is not a 5.

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?

The definition is dense but front-loaded, leading with the trigger condition before enumerating modes, coverage, and pricing. Parenthetical examples (add=, to=, region=) tie prose directly to parameter names. The single long run-on sentence with many parentheticals makes it slightly harder to scan than an ideal definition.

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 five-parameter, read-only calculation tool with no output schema, the description covers the modes of operation, geographic and temporal coverage, regional weekend variation, error behavior, and cost. The only remaining gap is the exact response format, which is modest given that it already mentions returning a holiday name. An agent has enough to select and invoke it 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?

Schema coverage is 100%, so the baseline is 3, but the description adds meaning by framing the parameters as distinct operating modes: check a date, add=N business days, or count business days to= a date. It also signals that region= narrows holidays to a state/province and that weekends may be non-standard. It does not state whether add= and to= are mutually exclusive or how they interact if both are supplied.

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 names specific verbs and resources: test whether a date is a business day, get previous/next business day, add N business days (add=), and count business days to a date (to=). It also states coverage (247 countries, 2026-2028) and regional granularity, so the capability is unambiguous. It does not explicitly differentiate itself from siblings like public_holidays or trading_day, keeping it below 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?

It opens with an explicit trigger: 'Use when an agent must know if a date is a business day in a country, or compute a due date.' That is clear when-to-use context covering both the query and calculation modes. It gives no when-not-to-use guidance and never routes the agent to public_holidays or trading_day for holiday-only or market-only questions.

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