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

Annotations only cover read-only/idempotent/open-world traits; the description goes well beyond by disclosing DST-gap handling (spring-forward times shift to the first valid instant and are flagged) and the paid access model (x402 USDC on Base, $0.001 per successful call, PaymentRequired object returned when unpaid). These are exactly the behavioral facts an agent needs and that no structured field supplies.

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 sentences, front-loaded with the usage trigger, and the output-field enumeration is dense but informative. Slightly heavy on listing return fields, though with no output schema that detail is justified.

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, so the description carries the return-value burden itself and does so (date, weekday, UTC offset, DST flag, UTC instant). It also covers the payment prerequisite and DST edge case, leaving nothing an agent needs to call it correctly unstated.

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 the schema already documents time, from and to with formats and defaults. The description adds only marginal parameter-level detail, restating that the source may be a wall-clock time or an ISO instant; baseline 3 is appropriate.

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 (convert a wall-clock or ISO instant into target zones) and enumerates the returned fields. It is clearly distinguishable from time_now, which reports the current time rather than converting a supplied instant.

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 for scheduling across time zones" gives a clear triggering context, and the mention of accepting either a wall-clock time or an ISO instant clarifies input scenarios. However, it never names an alternative tool or states when not to use this one.

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