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

Annotations cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower. The description adds real behavioral context beyond that: the return is copy-pasteable expressions keyed per calendar, and the 'holidays: true' calendars must be placed in daysOff rather than calendars, which is a non-obvious semantic rule.

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 dense sentences with the core purpose front-loaded and the holidays caveat following. No filler, though the holidays sentence packs two instructions that could be split for readability.

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 parameters and no output schema, the description is the only guide to the return value, and it does describe the content (expressions per calendar) and a key edge case. It could say whether the result is a list or a map keyed by calendar name, but it is sufficient to call and use correctly.

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 schema has nothing to document and the baseline for this dimension is 4. There is no parameter syntax the description needs to compensate for.

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 resource and the concrete output form: stdlib expressions for rules.js, one per calendar, with an inline example. This is clear enough to distinguish it from list_calendars, though it never names that sibling or explicitly contrasts the two.

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 implied through the destination of the output (rules.js) and the holidays/daysOff rule, which tells the agent how to act on holiday calendars. However, there is no explicit when-to-use-vs-list_calendars guidance or stated prerequisites.

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