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

Annotations already cover read-only and non-destructive semantics, so the description wisely spends its words on other traits: the mandatory explicit reference timestamp, a 1,830-day search horizon, and a 20-run cap strictly after the reference. It does not discuss timezone database versioning or ordering guarantees, but the operational boundaries are disclosed well beyond the annotations.

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?

Four sentences, each carrying distinct information: purpose, supported syntax, execution constraints, and exclusions. The capability statement is front-loaded and nothing is padded.

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?

Given an output schema exists, the description needn't explain return values; it instead covers the inputs' constraints, search bound, and unsupported syntax. An agent has everything needed to call this correctly and to recognize invalid inputs.

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%, so a baseline of 3 applies. The description earns above baseline by documenting the supported cron subset (numeric *, lists, ascending ranges, steps) and reiterating 'strictly after' reference semantics and the 20-run ceiling — grammar details the schema does not supply.

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 concrete verb and resource ('explain a five-field cron expression') and enumerates the three capabilities: explanation, next runs in an IANA timezone, and DST transition inspection. It also states what the tool is not ('Does not execute jobs'), which removes the most plausible misreading.

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 when you want to ...' gives an explicit trigger condition, and the closing sentence lists unsupported inputs (names, macros, seconds, years, ?, L, W, #) so the agent knows when to look elsewhere. There are no sibling tools, but the exclusions cover the main failure modes.

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