get_user_username

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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false. The description echoes these ('READ-ONLY', 'Makes no changes') but adds the API endpoint and category. No additional behavioral traits (e.g., auth needs, rate limits) are disclosed beyond annotations.

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 mostly concise with a clear emoji and API path. However, it contains redundancy ('Retrieve a user by username' appears twice, and 'Fetches data. Makes no changes.' could be merged). Still, it's compact and front-loaded.

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 low complexity (1 param, no output schema), the description covers the core functionality and safety. It lacks mention of error conditions or response structure, but the tool is simple enough that the description is largely adequate.

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% with a clear parameter description ('Username of the user you want to view'). The description does not add extra meaning beyond the schema, which is sufficient for a single, self-explanatory parameter.

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 tool retrieves a user by username, using specific verb 'Retrieve' and resource 'user by username'. It distinguishes from siblings like get_user (likely by ID) and get_user_email (by email), providing clear scope.

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?

The description indicates read-only usage ('READ-ONLY', 'Fetches data. Makes no changes'), implying safe use without side effects. However, it does not explicitly guide when to use this tool over siblings like get_user or get_user_email, nor mention prerequisites or alternatives.

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