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

Annotations already declare readOnly, idempotent, closed-world and non-destructive, so the safety profile is fully covered. The description adds that the tool returns parsed fields, a human-readable description, and upcoming ISO timestamps, but since an output schema exists this is largely redundant rather than genuine extra behavioral context.

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 short sentences, front-loaded with the verb+resource and followed by purpose and return value. Nearly every sentence earns its place, with only minor redundancy given the existing output schema.

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 simple 2-parameter read-only tool with an output schema and full annotation coverage, the description is essentially complete. The one gap is the relationship to the cron_parse sibling, which an agent would have to resolve on its own.

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% – both expression and next_runs_count are documented in the schema with examples and ranges. The description reinforces the 5-field constraint and the next-run preview, but adds no syntax or format information beyond the schema, matching the baseline 3.

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 ('Validate a 5-field cron expression') plus two concrete adjacent capabilities (explain the schedule, preview next runs). It is clear what the tool does, but it never distinguishes itself from the sibling cron_parse, which plausibly covers the same parsing/explaining ground.

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 this to debug cron jobs before they reach production' gives a usage context, so guidance is implied rather than absent. However, there is no when-not guidance, no mention of the cron_parse alternative, and no statement about how to handle 6-field (seconds) expressions besides the implicit rejection.

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