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

Annotations already indicate readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds the 'live member count' detail, which suggests real-time computation rather than a cached count—a useful behavioral nuance beyond the annotations. No contradictions with annotations exist.

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 a single, tightly worded sentence that conveys the tool's purpose and key outputs. There is no redundancy or filler; every word adds value.

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 is simple: one required parameter and a clear output intent. The presence of an output schema means return values need not be expanded in the description. The description covers the essential scope of the tool completely for an agent to select and invoke it correctly.

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%: the only parameter, segmentId, is fully described as 'The segment ID.' The tool description adds no extra meaning about the parameter. Per the rubric, high schema coverage yields a baseline of 3, and the description does not enhance it.

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 clearly states the tool's function: 'Get customer segment details including type, criteria, and live member count.' This specifies the verb (get), resource (customer segment), and the particular aspects returned (type, criteria, live member count), distinguishing it from siblings like list_segments (which lists segments) and get_segment_members (which returns members).

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 implies the appropriate usage context by enumerating what the tool returns. An agent can infer this is for retrieving metadata of a specific segment rather than listing all segments or getting member lists. However, there is no explicit guidance on when to avoid this tool or alternative options, so it falls just 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.