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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety and external-data behavior are covered. The description adds important non-schema context: free-tier limits, paid fallback via x402/card credits, in-band payment location, and the fact that date converts the result into an is_holiday answer. It does not explain error or pagination behavior, but the added pricing/payment context is substantive.

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 description is reasonably short, but it leads with billing and free-tier details before stating the tool's core purpose. The key 'what it does' sentence comes after payment mechanics, which is less front-loaded than ideal for tool selection.

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?

Given the presence of an output schema, the description need not explain return values. It covers the core scope, date behavior, pricing/payment, and country coverage, which is most of what an agent needs for this 3-parameter, read-only lookup tool. Remaining gaps are minor: year default behavior and country code format are left to the schema.

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%: country is described as 'ISO2', year is an enum, and date has no schema description. The description compensates for date by explaining 'date=YYYY-MM-DD answers is_holiday' and implies the year scope, but leaves year default/behavior and country format underexplained in the prose. This is a partial, not full, compensation for the low schema coverage.

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 states a specific resource and scope: 'Public holidays for ~490 countries/territories for 2026 and 2027', and explains the optional date=YYYY-MM-DD behavior. It is clear what the tool returns, though it does not explicitly differentiate itself from any similar sibling tool.

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?

The 'When to use' sentence says to use holidays to list public holidays or test one date for a country, which gives basic usage context. However, it restates the obvious rather than explaining when not to use it or naming an alternative tool.

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