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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description still adds real context beyond them: exact daylight-saving handling (the key correctness risk for this domain) and a per-call cost of 1 credit, neither of which appears in the annotations or schema.

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?

Front-loaded with the core capability, followed by cost, output format, and a compact per-op return-shape summary in a single dense block. Nothing is wasted, though the inline JSON shape listing is terse and requires careful reading.

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 usefully discloses the return shape for all three ops (convert/info/list), plus cost and DST behavior, which is substantial coverage for a 7-parameter tool. Remaining gaps are minor: error behavior for invalid zones and how fixed-offset inputs interact with DST are left implicit.

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 86%, and the schema itself already labels each parameter with its owning op and conditional requirements (e.g. from_tz required when datetime has no offset). The description's per-op output shapes and the 'country -> zones' mapping reinforce semantics but do not add meaning the schema lacks, so the baseline 3 applies.

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 opens with a specific verb+resource ('Convert a date and time between IANA time zones') and then enumerates the two other modes (inspect a zone, list a country's zones), so all three operations exposed by the `op` enum are named and distinguished. No sibling tool in the list overlaps with timezone conversion, so there is no ambiguity to resolve.

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 description effectively routes the agent: convert for datetime conversion, info for offset/transitions, list for enumerating a country's zones, and the schema param descriptions tie each parameter to its op. What is missing is an explicit 'when not to use' or edge-case guidance (e.g. choose info when you don't have a datetime), so it is clear context rather than full conditional guidance.

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