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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds the Mon-Fri convention and holiday behavior, but it does not clarify whether holiday exclusion is a toggle or simply inferred from the country parameter, and the restated return shape is redundant with the output schema.

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 tight sentences with the core behavior front-loaded; the trailing 'See list_bundles' cross-reference is short but slightly tangential to invocation. Overall efficient with almost no waste.

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 an output schema present, the return shape need not be explained, and annotations cover the safety profile, so the description only needs to convey the calculation rule, which it does. The only gap is the mild ambiguity around whether French holiday exclusion is always applied for country=FR.

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 100%, so the schema already documents start_date, end_date and the country enum. The description reinforces the weekday and French-holiday semantics but adds no new format or constraint detail beyond what the schema provides, making baseline 3 appropriate.

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 and resource ('Count working days') and pins the scope precisely with 'Mon-Fri between two dates'. This distinguishes it from the many date-counting siblings such as calculate_days_between, since it declares the day-of-week and holiday rules that define its output.

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 closing pointer to list_bundles gives some context for discovery, but there is no explicit when-to-use or when-not-to-use guidance, and it never names a competing tool like calculate_days_between or calculate_leave_days. Usage must be inferred from the purpose statement.

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