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

Annotations already establish read-only, idempotent, non-destructive, but the description adds real behavioral substance: tz-database backing, DST edge cases at the spring-forward/fall-back boundaries, and an explicit warning on non-existent or ambiguous times. It also discloses the exact return shape including the optional 'warning' field, which no annotation or output schema covers here.

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 a 'Use when' clause, and every sentence carries information, including the return-shape contract. The single dense paragraph makes the return-structure sentence slow to parse, which is the one structural cost.

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 compensates by enumerating the response object's fields, including the conditional 'warning' and 'day_note'. For a four-parameter, read-only conversion tool this leaves nothing an agent needs unknown before calling.

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% and the schema already lists most accepted time formats, so the description's value is partly repetition. It does add genuine meaning: the 'no Z' constraint on ISO input and the clarification that the date default is 'today in the source zone' rather than UTC today.

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 and resource ('convert a specific wall-clock time from one place to others') with an explicit scope qualifier ('for any date'). The contrast with meridian_now and meridian_meeting_slots is implicit but unmistakable, since this is the only tool framed around converting an arbitrary given wall-clock time.

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 leading 'Use when you need to convert a specific wall-clock time' gives clear triggering context, and 'for any date' rules out a now-only read. It never names an alternative or an exclusion, so an agent must infer when meridian_zone_info or meridian_meeting_slots would be the better pick.

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