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

The description adds the HTTP method and endpoint, providing context beyond the annotations. However, it does not disclose whether setting an existing key overwrites the value or any validation behavior. Annotations already indicate idempotent and non-destructive, so this is acceptable but not rich.

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, well-structured sentence that front-loads the action and target, with 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?

For a simple attribute-setting operation with full parameter documentation, a clear purpose, and annotations indicating idempotency and non-destructive behavior, the description is complete. An output schema exists, so return values need not be described. A minor omission is lack of details on overwrite behavior, but this is not critical.

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 covers all three parameters with descriptions, achieving 100% coverage. The description does not add additional parameter-level context, but the schema already provides sufficient meaning.

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 action ('Set') and the target resource ('custom attribute on a messenger user'), and also provides the exact API endpoint. This is specific and distinguishes it from sibling tools like send-user-message or get-user-chat.

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?

No explicit guidance is given on when to use this tool versus alternatives. The description does not mention prerequisites, typical scenarios, or exclusions, leaving the agent to infer usage solely from the action.

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