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

Annotations already provide readOnlyHint=true and openWorldHint=false, covering the safety profile. The description adds valuable behavioral context beyond annotations: it explains that the input is interpreted as local time in the source timezone, that the output shows both UTC offsets to make DST transitions visible, and that it accepts IANA IDs or city names. This exceeds the minimal disclosure required and does not contradict 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?

The description is three sentences, front-loaded with the core verb and purpose. It efficiently conveys input format, output behavior, and accepted timezone formats without redundancy. It could be slightly tightened, but every sentence carries meaningful information and there is no fluff.

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 has an output schema (indicated by context signals), so return values are already covered. The description fully explains the input contract (local datetime, source/target timezones), the interpretation rule (local time without offset), and the output behavior (equivalent local time with UTC offsets for DST visibility). No critical information needed for correct invocation 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?

The schema description coverage is 100%, so all three parameters (datetime, from_tz, to_tz) are already documented with descriptions. The description reinforces the datetime format (no offset) but does not add substantive meaning beyond the schema. It mentions accepted formats for timezones (IANA IDs or city names), which is also present in the schema. Thus, baseline 3 is appropriate; the description adds no critical param semantics beyond what the schema provides.

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 states a specific verb ('Convert'), a precise resource (local datetime from one timezone to another), and explicitly defines input/output semantics. It distinguishes itself from the sibling ref_timezone_lookup (which implies lookup, not conversion) by describing the conversion action and output format.

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 description clearly conveys when to use the tool (converting local datetimes between timezones) and provides usage context (input is local time without offset, output shows both UTC offsets). It does not explicitly mention when not to use it or name the lookup sibling as an alternative, but the conversion purpose is unambiguous enough to imply selection over a lookup tool.

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