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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so 'Read-only' in the description is pure duplication and earns no credit. The only genuinely new behavioral claim is 'same data and limits as GET /v1/countries', which gestures at rate/size limits without stating them. Adds a little beyond the structured fields, but not much.

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?

Two short sentences, front-loaded with the resource and its contents. The second sentence's 'Read-only' clause duplicates the annotation and does not earn its place, but the cost is only two words. The API-path reference is a compact way to signal parity with a known endpoint.

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 no-parameter, read-only enumeration with an output schema (so return values need no explanation) and full annotation coverage, the description is nearly sufficient. Its one soft spot is the vague 'same data and limits as GET /v1/countries' — an agent with no REST context cannot resolve what those limits are.

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 tool takes zero parameters, so the baseline is 4; there is no parameter semantics to add or omit. Nothing in the description is needed here.

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 (List) and resource (supported countries) and enumerates the payload contents: ISO codes, regions, and the supported year range. The sibling set (add_business_days, business_days_between, get_holidays, is_business_day) has no overlapping function, so no sibling disambiguation is required. An agent knows exactly what this returns without opening the schema.

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?

There is no explicit 'use this when' statement and no alternatives to compare against, but the listed contents (ISO codes, year range) make the purpose obvious: validating inputs for the holiday/business-day siblings. Usage is implied rather than stated, which lands at the minimum-viable level.

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