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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description still adds substantive behavior: what is returned (local wall times plus UTC ISO, plain-English field breakdown, DST gap/fold warnings), the UTC default, and why the computation is non-trivial. That is real context beyond the structured fields.

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 the trigger condition, then parameters, then return shape, then exclusions — a sensible order with no filler sentences. The platform enumeration (GitHub Actions, Vercel cron, Cloudflare Cron Triggers, systemd, agent schedule) is slightly verbose but aids retrieval matching.

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 4-parameter read-only utility with no output schema, the description covers when to call it, defaults, and the full return payload including DST edge-case warnings. An agent has everything needed to call it correctly and interpret the result.

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 the baseline is 3; the worked example ({"expression":"0 9 * * 1-5","timezone":"America/New_York","count":5}) usefully shows how the parameters combine in practice. It does not mention the optional 'from' parameter, which would have made the parameter story complete.

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 verb and resource: computing the next fire times of a cron expression, in a given IANA timezone. It explicitly separates itself from meridian_convert_time and stamp_check_dns_record, so an agent can pick it out of a 30-tool sibling list without opening a 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?

Gives a concrete trigger ('when you or the user just wrote a cron expression ... before claiming it is correct'), an explicit anti-pattern ('Do not guess next runs yourself — DST rules differ by region and year'), and two named exclusions routing to Meridian and Stamp. Nothing is left to inference.

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