users_exists

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

With no annotations, the description carries the behavioral disclosure burden. 'Check whether' implies a read-only existence check, and '(admin)' discloses a privilege requirement. However, it does not explicitly state that the operation has no side effects or what happens when the account does not exist; the output schema may cover return values.

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 extremely concise, front-loaded with the core purpose, and contains no redundancy. Every word contributes meaning, and the parameter note is clearly separated.

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 existence check with an output schema, the core information is present. However, it lacks sibling differentiation and explicit usage context, which is notable given the large list of related user-management tools.

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 0%, so the description must clarify the parameter. It describes username as 'Candidate username', which adds the notion that this is the proposed name to test. This is minimal but sufficient for a single string parameter, though it lacks format or case-sensitivity details.

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 a specific verb and resource: 'Check whether an account name already exists'. The '(admin)' suffix adds an audience hint. It does not explicitly differentiate from sibling tools like users_search or users_list_all, but the existence-check semantic is distinct enough.

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 about when to use this tool versus alternatives such as users_search or users_list_all. The '(admin)' marker implies an admin-only context, but there are no conditions, exclusions, or reasons for choosing this tool.

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