Cron explain

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

Annotations already declare readOnly/idempotent/closed-world, and the description goes well beyond them: it discloses evaluation semantics ('when both day fields are restricted a day matches either one'), failure behavior (Quartz syntax rejected, per-field errors reported), and the timezone context of the returned run times. That is exactly the subtle behavior an agent cannot infer from annotations or schema.

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?

A single dense paragraph that is front-loaded with the core action and supported syntax before edge cases; almost every clause carries information. The trailing web-version URL is the only element that does not help an agent call the tool, and the long parenthetical syntax list is heavy but purposeful.

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 five parameters, no output schema, and rich syntax rules, the description covers the gaps: it states both return components (plain-English explanation plus upcoming run times), the timezone basis for those times, and error behavior. Nothing an agent needs before invoking it 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 description coverage is 100%, so the parameters are already fully documented. The description only implies the expression and timezone parameters and says nothing about 'from', 'count', or 'hour12' that the schema does not already say better. Baseline 3 for a schema-complete tool.

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?

Names a specific verb and resource ('Explain a standard 5-field cron expression ... in plain English and list the next run times'), and enumerates the exact accepted syntax (names, ranges, lists, steps, ?, @-macros) while explicitly excluding Quartz 6/7-field and L/W/# syntax. An agent knows precisely what it gets and what it will not get, which is stronger differentiation than the sibling list (all unrelated calculators/converters) requires.

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 usage envelope is clearly stated: standard 5-field Vixie cron only, Quartz extensions rejected with a clear message, IANA timezone context. It does not name an in-server alternative (none exists among siblings), and the external web-version link is a de facto alternative pointer rather than a routing rule. Clear context, but no explicit 'use this when / do not use when' framing.

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