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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful context beyond that: the definition used (weekend plus Nager.Date public holidays), which tells the agent the result depends on an external holiday dataset and may vary by country. It stops short of stating the boolean return or invalid-date behavior, keeping it below a 5.

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?

A single front-loaded sentence with no filler; the predicate, the input format, and the holiday definition all earn their place.

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 two-parameter predicate with full schema coverage and read-only annotations, the description supplies the one thing structured data cannot: what counts as a business day. Only the boolean return value and behavior on malformed dates are left implicit.

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%, and the schema already documents the YYYY-MM-DD format and the ISO 3166-1 alpha-2 country defaulting to US. The description restates those formats rather than adding new semantics, so the 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?

The description names a precise predicate (whether a date is a business day), the accepted date format, and the country scoping, so the agent knows exactly what question the tool answers. It does not explicitly contrast itself with the sibling add_business_days, which performs a related but different calculation.

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?

Usage is only implied: the tool answers a boolean calendar question, so it is inferable when to call it. There is no explicit when-to-use, when-not-to-use, or pointer to the sibling add_business_days for the opposite direction of the same domain.

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