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

Annotations already declare readOnly, openWorld and non-destructive, so safety is covered. The description adds useful return semantics (nationwide vs regional flag plus holiday name), which matters because there's no output schema. It says nothing about external-source latency, failure modes for unknown country codes, or why idempotentHint is false for what is ostensibly a pure lookup.

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?

Three short lines, each earning its place: what it returns, when to reach for it, and a concrete call example. The purpose and the returned detail are front-loaded before the use-case clause.

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 does the necessary work of naming the response fields (holiday name, nationwide/regional). What's missing is edge-case behavior an agent needs for correct interpretation - unknown country codes, dates with no holiday, and the idempotentHint=false discrepancy.

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%: date format, default of today (UTC), and country code/name are all documented in the schema. The description's example payload confirms shape but adds no syntax or validation meaning beyond the schema, so baseline 3 applies.

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 check (whether a date is a public holiday) with the resource scope (country, nationwide vs regional) and the returned name, so the semantics are clear. It does not name or distinguish itself from the siblings next_public_holidays and public_holidays, which an agent could otherwise confuse with a single-date check.

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 when: deciding if offices, banks or schools are closed' clause gives concrete decision context, including the practical consequence of the answer. It supplies no exclusions or explicit alternative (e.g., 'for a list of holidays, use public_holidays instead'), so the routing against siblings is left to inference.

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