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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds genuinely new context: the Croner dialect constraint, DST transition behavior (skipped and repeated wall-clock times), and the fact that no account or token is needed. It doesn't state the 50-item cap or output shape, but the cap lives in the schema and the output schema covers returns.

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?

Front-loaded with purpose, then clearly labeled 'When to use', 'Notes', and example blocks. Every sentence carries information an agent needs; the labeled structure makes it scannable in one pass.

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 read-only, idempotent preview tool with an output schema and full schema coverage, the description covers the dialect, timezone requirement, DST nuance, and example invocation. Nothing needed to call it correctly is missing.

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 coverage is 100%, so baseline is 3; the description raises it by adding a concrete example argument set that shows how expr, tz, from, and count combine, plus the 'strictly after from' semantics echoed in prose. Dialect and domAndDow remain schema-only, so it doesn't fully take over parameter explanation.

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?

Opens with a specific verb and resource: 'List the next run times of a 5- or 6-field cron expression (Croner dialect) in an explicit IANA timezone,' and adds the DST edge-case scope. No sibling tool does cron previewing, so this is instantly distinguishable from the surrounding validation/lookup tools.

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 explicit 'When to use:' line gives a concrete trigger ('before deploying or explaining a cron schedule, especially across daylight-saving changes'). There are no competing siblings to route away from and no explicit 'when not to use' clause, which keeps it just short of a 5.

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