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

With no annotations, the description carries the full burden of behavioral disclosure, but it only says what the tool lists. It does not state that it is a read-only operation, whether results are paginated, what authentication or permissions are required, or how the required contact_id filter affects the output.

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 consists of two tight sentences with no wasted words. The core purpose is front-loaded, and the use case follows naturally.

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?

For a simple one-parameter list tool with no output schema, the description is adequate but misses a key detail: it does not mention that contact_id is required and acts as a filter, so an agent relying on the description alone might assume it lists all label values. It also omits any return-format or pagination context.

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%, so the single contact_id parameter is fully documented in the schema. The description adds no additional meaning about the parameter, making the baseline score of 3 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 states a clear verb ('Lists') and resource ('custom label values (tags) associated with contacts'), making the tool's function immediately clear. It does not explicitly differentiate itself from siblings like listContacts or listCartLabelValues beyond the resource noun, so it falls short of a 5.

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 offers a use case ('Useful for filtering or identifying contacts...'), which implies when the tool might be helpful. However, it provides no guidance on when to choose this over alternatives such as listContacts, nor does it mention any preconditions or exclusions.

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