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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new operational context beyond the annotations: the call costs 2 credits, which matters for an agent deciding whether to invoke a lookup tool repeatedly. It does not explain error behavior for ambiguous or unknown cities, which is the main remaining gap.

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?

Two short sentences, front-loaded with the outcome and tail-loaded with the cost and response detail; every clause carries information. The only waste is the redundant 'Timezone Lookup: Timezone Lookup' prefix, which restates the title before the real content begins.

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?

The tool is simple, an output schema exists so return fields needn't be re-explained, and annotations cover the safety profile. The description adds the two things structured fields don't carry: the credit cost and the alternate identifier forms. Missing only the edge-case behavior (unknown city, both params given), which is minor for a stateless lookup.

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 100% and both parameters carry examples, so the baseline is 3. The description earns above baseline by framing the two parameters as alternative input forms ('any city or IANA zone name'), telling the agent it can resolve either identifier shape rather than requiring both. It still doesn't state precedence if both are supplied.

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 uses a specific verb+resource formulation: it 'resolves any city or IANA zone name to its local time, UTC offset, and calendar date', which is far more precise than the tautological title. An agent can immediately understand what comes back. It loses a point because it never distinguishes itself from close siblings such as WorldTime or MeetingTimeConverter, which appear to cover overlapping ground.

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 only implied by the purpose statement — if you need a zone's current local time, this is the tool. There is no explicit when-not, no routing to WorldTime/MeetingTimeConverter, and no statement about whether the caller should supply city, timezone, or both. With 0 required parameters, an agent has no guidance on the minimum viable call.

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