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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description adds value by stating that it returns parsed fields, a human-readable description, and ISO timestamps, which is beyond annotation coverage and sets proper expectations for the output behavior.

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 sentences, front-loaded with the primary action, a clear use case, and a concise output summary. Every sentence earns its place with no redundancy.

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 two well-described parameters, an output schema, and strong annotations, the description fully covers what an agent needs: purpose, usage, and return value highlights. The mention of ISO timestamps helps set format expectations, making this complete for the tool's complexity.

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 well-documented. The description refers to '5-field cron expression' and 'upcoming ISO timestamps,' which aligns with schema but adds no new parameter semantics beyond what is already present.

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 ('Validate', 'explain', 'preview') applied to a clear resource ('5-field cron expression'), and it distinguishes itself from sibling cron_parse by adding validation and preview functionality. This is precise and unambiguous.

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 explicitly gives a usage context: 'Use this to debug cron jobs before they reach production.' It doesn't mention when not to use it or name alternatives, but the use case is clear enough to guide an agent toward appropriate selection.

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