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

Annotations already cover the safety profile (read-only, no open-world access), and the description adds substantive behavioral rules beyond them: the 13-digit millisecond cutoff, UTC default for timezone-less dates, and explicit error reporting for unreadable dates and unknown zones. It does not describe output structure beyond naming formats, but that gap is minor here.

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, each carrying distinct information: purpose and outputs first, then input-parsing rules, then error behavior. Nothing is repeated from the name or schema, and no sentence is filler.

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 return formats, and it also covers the two edge cases (millisecond inference, missing timezone) plus failure modes. For a two-parameter read-only utility, nothing an agent needs to invoke it correctly is missing.

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 baseline would be 3, but the description adds real meaning the schema does not: the digit-length heuristic that governs how `value` is interpreted, and how timezone-less date input is treated relative to the timeZone default. This is genuine semantic value on top of the structured fields.

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) and resource (Unix timestamp or date) plus the full set of target formats, which makes it immediately distinguishable from siblings like convert_units or format_json. An agent knows exactly what comes out of the call without opening the schema.

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?

The domain of use is implied by the name and the accepted input formats, but there is no explicit when-to-use guidance, no exclusions, and no mention of when a sibling tool would be preferred. Adequate but leaves routing entirely to the agent's inference.

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