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

Beyond the readOnly/idempotent annotations, it discloses that computation happens locally against the IANA database, that there are no rate limits, that results are exact, that the tool is free, and that failures surface as isError with a message and no charge. That is genuinely useful operational context; only the mild tension between 'computed locally' and openWorldHint=true keeps it from a 5.

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?

One dense paragraph, front-loaded with the three capability groups before operational details. Price and error notes are compact, though the trailing cost/failure sentence is slightly less essential than the leading capability enumeration.

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?

An output schema exists, so return values need not be described, and the description covers the multi-mode nature, zone format, and error behavior for a 5-param, zero-required tool. The one residual gap is what a bare call with no arguments returns, which is only loosely implied by 'Current time in any time zones'.

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 every parameter including defaults, maxItems, and the 'naive times are read in from_tz' rule. The description adds the IANA zone-name convention and examples, but no deeper interaction semantics (e.g., how add combines with until). Baseline 3 applies when the schema does the heavy lifting.

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 names specific verbs and resources across all modes: current time in zones, zone-to-zone conversion (DST-correct), and date arithmetic (add/subtract durations, days between, weekday, ISO week, Unix time). It is clearly distinguishable from the similarly-named sibling unit_convert because it is scoped to time zones and calendar math.

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?

It enumerates the capabilities, which implies when the tool is applicable, but never states when NOT to use it or names an alternative (e.g., unit_convert for non-time unit conversion, sun_moon for celestial events). Usage is inferable rather than prescribed, which fits a 3.

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