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

Annotations already establish read-only, idempotent, non-open-world behavior, and the description adds genuinely new traits beyond them: the per-call price and payment rail ($0.05 via x402/USDC on Base) and the no-DST empty-list semantics. It still doesn't disclose rate limits or output ordering, but the added context is substantive.

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 purpose, then the return contents, then edge case, then price. Dense but every sentence carries information; the pricing sentence is somewhat extraneous to invocation but is legitimately relevant to an agent deciding whether to call.

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 steps in to describe the return shape (exact instant, offset before/after, jump forward/back, current offset/DST state, next transition) and the no-DST edge case, which is exactly what an agent needs. Minor gaps remain around ordering and pagination for multi-year ranges.

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%, so 'from', 'zone', and 'years' are already fully documented in the schema. The description restates the range and from-instant concepts but adds no syntax, format, or default detail beyond what the schema provides — 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?

Opens with a specific verb+resource ('DST transitions: list the daylight-saving time changes for an IANA time zone') and states the scope (date range) plus exactly what each result contains. This is clearly distinguishable from sibling timezone_convert, which converts a timestamp rather than enumerating transitions.

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?

It gives clear context for when the tool applies (IANA zone + date range, next transition from a given instant) and an edge-case rule (zones without DST return an empty list, not an error). It never explicitly names an alternative sibling or a when-not condition, so it falls short of a 5.

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