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

Annotations already declare readOnlyHint=true and openWorldHint=true, so the safety profile is covered; the description adds genuinely useful behavioral context beyond them: DST-aware time-zone handling, supported format variants (5-field, 6-field, names, macros), and the $0.001 USDC cost with trial status.

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?

Three tight sentences: capability first, then supported formats, then price/trial. No padding, and the core function is front-loaded before commercial details.

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 an output schema present, return values need not be described, and the description covers formats, time-zone handling, and limits adequately for a read-only explanation tool. Only the absence of usage guidance keeps it from being fully complete.

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 tz, count, and expression parameters are already well documented with defaults, ranges, and examples. The description's mentions of 'any time zone' and format support only lightly reinforce what the schema already conveys, so the baseline 3 is appropriate.

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 pair (validate + explain) and resource (cron expression), then enumerates the exact outputs: plain-English meaning, per-field expansion, and next run times. Clearly separable from other 'explain' siblings like regex-explain or sql-explain.

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 implies its use case (you have a cron expression and want it explained/validated) but never states when to reach for it versus an alternative or any prerequisite. No explicit when/when-not guidance is present.

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