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

Annotations already declare this is a non-readonly, non-destructive, non-idempotent mutation. The description adds useful behavioral context beyond that: permissions required, inclusive start-to-end semantics, and that the whole calendar is returned. It does not explain duplicate handling, but the main mutation behavior is well covered.

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 sentences, front-loaded with the core action and mode selection, followed by permissions and return behavior. There is no wasted language.

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 four-parameter mutation without an output schema, the description covers the essential context: who can call it, how holiday versus personal leave is selected, inclusive date behavior, and that the full calendar is returned. Minor edge cases like duplicate entries are unspecified but not critical.

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 parameters are already documented in detail. The description reinforces the userId distinction and inclusive date range but adds little beyond what the schema already states.

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 states a specific verb and resource: adding a holiday for everyone or a personal leave for one user. It clearly distinguishes the two modes via omission or inclusion of userId, so an agent can tell what the tool does 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?

It gives clear usage conditions: omit userId for a company-wide holiday, include userId for one person's leave, and notes the required Administrator or ProjectManager role. It lacks explicit exclusions or reference to the sibling remove_day_off, but the context is still clear.

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