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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description's value is in what it adds: DST-aware offset handling, a hard cap of 20 target zones, an enumerated return payload, and a metered cost of $0.003 USDC per call via x402 on eip155:8453. That payment requirement is exactly the kind of behavioral fact an agent cannot get from structured fields.

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 dense sentences, front-loaded with purpose and then inputs, outputs, limits and price. The opening clause repeats the title nearly verbatim, which is the only wasted space.

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, and the description does the necessary work by enumerating what comes back (UTC plus each target zone with offset, weekday, ISO week, day of year, unix s/ms, RFC 2822). For a three-parameter, all-optional read tool this is close to complete; only error behavior and an output example are absent.

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?

With schema coverage at 67% and the 'time' property carrying no schema description at all, the description compensates by specifying accepted input forms (ISO 8601, unix seconds/ms, 'now') and the from-zone interpretation of offsetless input. It also restates the 20-zone ceiling for 'to'. It does not explain the comma-separated string form versus array form beyond the schema's own note.

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 (convert) plus the resource (a time) and the two axes of conversion (time zones and formats), naming the supported representations. It is clearly distinguishable from siblings like time_diff (differences) and unit_convert (physical units).

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 rather than stated: nothing tells the agent when to pick this over time_diff, or what happens if no target zone is supplied. The input conventions (bare local time read in the 'from' zone, 'now' accepted) do give real operational guidance, which lifts it above a bare 2.

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