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

Annotations already declare readOnlyHint=true, but the description adds valuable behavioral context by defining transition timestamps: 'Transition timestamps are the first instant the new offset is in effect.' This clarifies a potentially ambiguous aspect of the returned data. It also specifies that inputs without a UTC offset are read as UTC (in the schema, but the description reinforces the tool's deterministic behavior).

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 two sentences long and front-loaded with the tool's purpose. It efficiently packs the key details: inputs, outputs, and a semantic clarification about DST transitions. No unnecessary words or repetition.

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 enumerates all return values (UTC offset, DST active, transition instants, abbreviation) and clarifies the transition timestamp meaning. It also includes a usage note. This is complete for a read-only informational tool, especially given the rich parameter schema.

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 input schema provides 100% coverage with detailed descriptions for both parameters (date format and timezone example). The description does not add any parameter-specific semantics beyond what the schema already covers, so a baseline score of 3 is appropriate.

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 ('returns') and clearly identifies the resource (timezone details for an IANA timezone and date), listing exact outputs: UTC offset, DST active flag, DST transition timestamps, and abbreviation. It also differentiates from sibling tools by emphasizing 'DST behavior before scheduling,' which is distinct from timezone conversion (tz_convert).

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 explicitly states when to use this tool: 'Use this to understand DST behavior before scheduling.' This gives clear context. However, it does not mention when not to use it or name any alternative sibling tools, so it falls short of full explicit exclusion/alternative guidance.

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