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

The description 'Fetch' is consistent with the readOnlyHint annotation. Adds endpoint context but no additional behavioral details beyond annotations. No contradictions.

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?

Two efficient sentences with no wasted words. Front-loads the core purpose and includes the API endpoint for developer reference.

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?

Given the small parameter count, read-only annotation, and no output schema, the description sufficiently covers the tool's functionality. Could optionally mention the response shape but 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?

Schema coverage is 100% as the description for user_id matches the parameter description. The description restates the schema info, adding no extra 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?

Clearly states the verb 'Fetch' and resource 'single user', specifies identifier types (user id or external id), and mentions the API endpoint. Distinguishes from sibling tools like list_users and create_user.

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?

Indicates when to use (fetch single user by id) but does not explicitly mention alternative tools or when not to use. However, the context of siblings implies the usage scope.

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