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

Annotations already declare readOnly/idempotent/non-destructive, and the description adds material context beyond them: the tzdb release is runtime-controlled so results are only deterministic per runtime, rules can change, and there is a paid call of $0.0012 USDC via x402 on Base mainnet. Payment/auth requirements are exactly the kind of behavior an agent cannot infer from annotations.

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 operation before caveats and pricing; nothing is padding. The runtime/tzdb caveat is slightly compressed into one dense clause, but every sentence earns its place.

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 tool is simple with only two parameters. Purpose, determinism caveat, and cost are all covered; the only missing piece an agent needs is the default behavior of the optional `at` parameter.

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 0%, so the description carries the burden: it identifies `time_zone` as an IANA identifier and `at` as an optional ISO timestamp, which is meaningful beyond the bare pattern. However, it gives no example IANA value, no statement of what happens when `at` is omitted (current time?), and no note on how offsets are returned, leaving real gaps at zero coverage.

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 ('Resolve') and resource ('IANA time-zone identifier') plus the secondary operation ('convert an optional ISO timestamp'), and names the backing data source (Worker runtime time-zone database). An agent knows exactly what it gets, and no sibling in the list overlaps with time-zone conversion.

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?

'Use for deterministic local-time and UTC-offset calculations' gives a clear positive use case, and the note about government rules changing tells the agent when results may drift. There is no explicit when-not or named alternative, but no sibling tool is a plausible substitute, so the guidance is effectively complete.

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