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

The description discloses key behaviors beyond the readOnlyHint annotation: it is rule-based rather than a language model, it refuses out-of-grammar phrases instead of guessing, and it reports unused words as a correctness signal. This is exactly the kind of behavioral context an agent needs to trust and interpret the result.

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?

The description is front-loaded with the single-sentence purpose, then layers behavioral notes, delegation rationale, and ownership context in logical sections. No sentence is wasted; the ownership note earns its place by offering an alternative route.

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 one-parameter tool with no output schema, the description covers the input type, failure behavior, output semantics, and rationale for delegation. It gives an agent everything needed to decide, invoke, and interpret the call correctly. An example output shape would be nice but is not necessary given the clarity of 'into a cron expression.'

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?

The schema already documents 'phrase' with an example, so the baseline is 3. The description adds meaning by explaining that the phrase is an English schedule description and by revealing that extra or unrecognized words are not silently dropped but reported, which clarifies the expected input contract.

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 opens with a specific verb-resource mapping: 'Convert an English schedule description into a cron expression.' It also distinguishes the tool from a language model and from sibling cron_explain by making the direction of translation unambiguous.

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 'Why delegate this' section gives concrete conditions for using the tool, such as cron's OR-ing of day-of-month/day-of-week and the silent failure of expressions like February 30. It also notes the alternative of calling the owner directly. It doesn't explicitly name cron_explain as the reverse-use alternative, but the direction is clear.

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