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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint, so the repeated 'Read-only' sentence adds little. However, the description does disclose non-obvious behavior beyond the schema: a hard cap of 5 matches and conditional output (with a date, UTC offset and abbreviation for that day), plus plan/endpoint equivalence.

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 tight sentences that front-load the core purpose and then layer return behavior and plan context. The standalone 'Read-only.' sentence is redundant against the annotations and is the only wasted token.

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 an output schema present, the description need not explain return shape, and it still covers the search vocabulary, result cap, conditional date behavior, and read-only nature. Nothing needed 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 is 3. The description goes further by giving the query vocabulary ('tokyo', 'india', 'PST') and explaining the conditional effect of the date parameter, which the schema only labels loosely as 'for offsets/abbreviations'.

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 (look up) and resource (IANA time zone ids) plus the accepted key types (city, country, alias, raw IANA id) with concrete examples. The sibling find_meeting_overlap operates in a completely different domain, so no explicit differentiation is needed for an agent to select correctly.

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 implied by the description and title, but there is no explicit statement of when to prefer this tool, no prerequisites, and no exclusions. The mention of 'Same engine as GET /v1/zones/search on the free BASIC plan' is contextual routing information rather than usage guidance.

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