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

Goes well beyond the readOnly/idempotent annotations by disclosing DST edge-case behavior (spring-forward gaps shift to first valid instant and are flagged) and the payment mechanics ($0.001 via x402 USDC on Base, PaymentRequired on unpaid call). These are exactly the behavioral facts an agent must know 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?

Three sentences, front-loaded with the usage trigger, then conversion/DST semantics, then cost. Every sentence earns its place and nothing is repeated.

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?

With no output schema, the description compensates by enumerating the returned fields (date, weekday, UTC offset, DST flag, UTC instant) and covers the paid-invocation path. An agent has everything needed to call it 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 description coverage is 100%, so the schema already documents time, from, and to (including the offset-overrides-from rule). The description reinforces the wall-clock-vs-instant distinction but adds no new parameter-level detail, warranting 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 action and resource ('takes a wall-clock time in a source zone ... returns the same instant in each target zone') with the exact return fields enumerated. This clearly separates it from time_now and the fx_* siblings without needing to name them.

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?

Opens with an explicit when-to-use trigger ('Use for scheduling across time zones'), which gives clear context. It does not name alternatives (e.g. time_now) or state when-not-to-use, so it stops short of the 5 bar.

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