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

Annotations already establish the safe, read-only, idempotent profile, so the bar is lower. The description adds real context beyond that: the parsing semantics (Vixie OR rule, macros), DST-awareness, a hard cap of 50 results, and an explicit per-call price ($0.003 USDC via x402 on eip155:8453) that an agent needs before invoking.

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?

Two tight sentences, front-loaded with the purpose and then capabilities plus pricing. Dense but every clause earns its place; the pricing tail is slightly tacked-on but necessary.

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?

No output schema exists, yet the description states what comes back (next N run times in UTC and the given IANA zone, DST-aware), which covers the return contract. Combined with pricing and parse-feature disclosure, an agent has enough to call this correctly.

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 only 25%, so the description must carry meaning and it largely does: it explains the expression format (5-field, lists/ranges/steps/names/macros), the output time zone semantics for tz, and the count ceiling of up to 50. Only 'from' is left to the schema's one-line description, which is adequately covered there.

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 specific verbs (explain, list) plus the resource (cron expression / next run times) and scope (any time zone). It is trivially distinguishable from the nearest siblings like time_convert and time_diff, which do not parse cron schedules.

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?

Usage is implied by the purpose – an agent can infer it should call this for cron parsing/scheduling questions – but there is no explicit 'use when' or 'use instead of X' guidance. With no cron-specific sibling to route against, the omission is minor but still leaves context to inference.

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