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

No annotations are provided, so the description carries full responsibility for behavioral disclosure. It explicitly details the return format as {valid: bool, error?: string}, which tells the agent what to expect and implies a read-only, non-destructive operation. This adds useful behavioral context beyond a simple statement of purpose.

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?

The description consists of two short, focused sentences with no fluff. It states the purpose and the return format efficiently, earning each word.

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 simple validation tool, the description is complete enough: it covers the purpose and explicitly provides the return shape, compensating for the lack of an output schema. It could optionally mention supported cron syntax variants or error handling details, but those are not essential for basic usage.

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 input schema already provides a complete description of the 'expression' parameter with 100% coverage, so the baseline is 3. The tool description does not add any additional meaning or examples for the parameter, but the schema fully explains it.

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 clearly states the tool checks if a cron expression is valid, using a specific verb and resource. This distinguishes it from sibling tools like generate_cron, explain_cron, and next_runs, which serve different purposes.

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 description does not explicitly state when to use this tool or mention alternatives, but the purpose is so straightforward that usage is implied (i.e., when validation is needed). No exclusions or alternative comparisons are provided.

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