reach_countProfileSegmentContactsV1

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

With no annotations, the description carries the burden and does well by emphasizing 'count' and 'without listing them,' implying a read-only operation. It also discloses a performance trait ('Cheaper'), which is useful behavioral context. It does not explicitly state that no data is modified or describe the return format, but the behavior is sufficiently clear for a simple count tool.

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: the first states the core function, the second gives a usage tip. No filler, front-loaded, and every sentence 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 description explains what the tool does and why to use it, and the tool name clarifies the profile-segment context. It does not explicitly mention the return format (a count) or explain what profileUuid/segmentUuid refer to, but for a simple count operation, this is a minor omission. Overall, it is complete enough for an agent to use 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?

The schema provides descriptions for both parameters ('Profile uuid parameter' and 'Segment uuid parameter'), but they are generic and merely restate the names. The tool description adds no extra parameter guidance. Since schema description coverage is 100%, the baseline is 3.

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 'Count the contacts currently matching a segment' with a specific verb and resource, and explicitly notes 'without listing them,' distinguishing it from list endpoints. The tool name also aligns perfectly with counting profile segment contacts.

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 explicitly states when to use this tool: 'Cheaper than paging through the segment contacts endpoint when only the size is needed.' This gives a clear use case and implies the alternative of paging/list endpoints, without naming a specific sibling but providing sufficient context.

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