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

Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds meaningful behavioral context by specifying that dates are observed per OPM rules, which is a non-obvious detail since holidays can shift to weekdays. This goes beyond what the annotations alone provide.

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 a single, front-loaded sentence with no filler. Every part contributes: the verb, the resource, the time scope, and the OPM observation rule.

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 simple read-only tool with one optional parameter, the description conveys the essential output: a list of holidays with observed dates. There is no output schema, so a bit more detail about return fields or date formatting could help, but the description is adequate for the tool's simplicity.

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?

The schema has zero description coverage for the year parameter, so the description must carry the semantic load. 'For a year' only weakly signals the year parameter and adds little beyond the parameter's name. It does not explain accepted ranges, how OPM observation affects the parameter's meaning, or any other interpretation.

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 verb 'List' is explicit and the resource 'US federal holidays' is precisely scoped. Adding 'including observed dates per OPM rules' clarifies the exact content and distinguishes this holiday tool from business-day siblings like calendar_business_days_add and calendar_is_business_day.

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 use case is implied by the resource name, but the description never states when to choose this over the business-day sibling tools or when not to use it. There are no exclusions or conditional routing notes, so the agent has to infer usage from context.

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