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

Annotations already declare readOnly and idempotent, so the safety profile is covered. The description adds genuinely new context: the result is exactly five occurrences, returned in UTC regardless of the input timezone, and nothing is persisted — a non-obvious normalization worth stating.

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 sentence that front-loads the core purpose and ends with the key non-persistence constraint. No filler, no repetition of the title.

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?

There is no output schema, and the description compensates by specifying the return value (five upcoming start times, in UTC). Only error behavior for an invalid cron expression is unaddressed, a minor gap for a read-only preview tool.

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%, with both cron syntax forms and IANA timezone naming fully documented in the schema. The description only reiterates that both inputs exist and that output is UTC; it adds no syntax or format detail beyond the schema, so baseline 3 applies.

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 gives a specific verb ('Check') and resource ('cron expression and time zone') plus a concrete output ('next five start times'). The phrase 'without saving anything' implicitly separates it from create_schedule and run_schedule, though those siblings are never named.

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?

Use is implied as a dry-run/validation step before save_schedule or create_schedule, but the description never states when to prefer this over those tools or what to do when validation fails. The agent must infer the workflow.

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