get_user_by_username

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

With no annotations provided, the description carries full responsibility for disclosing behavior. It only states the basic action and offers no details on what is returned, whether authentication is required, case-sensitivity, error handling, or any side effects. For a read operation, some context is expected, but even the return format is not hinted at.

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 sentence with no wasted words, making it extremely concise and front-loaded. However, it is so brief that it borders on under-specification—it essentially restates the tool name without additional structure or context.

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 getter with one fully-documented parameter, the description is minimally viable. However, the lack of output schema and annotations means the description should provide more context about what the user object includes or any caveats. It is enough for a basic lookup but lacks completeness in a broader toolbox 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?

The schema description covers 100% of parameters, providing an example value ('MrBeast') that clarifies the expected format. The description itself adds no parameter information, but since the schema is complete, the baseline of 3 is 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 clearly states the action ('Gets') and the resource ('a user by username'), which aligns with the tool name. It is specific enough to distinguish from siblings that operate on user-related data like tweets or followers, though it doesn't explicitly differentiate from other user-lookup tools such as get_users_by_ids.

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 provides no guidance on when to use this tool versus alternatives. It doesn't mention whether to prefer this over get_users_by_ids, or any context about use cases, prerequisites, or conditions. This is a clear gap given the large number of sibling tools.

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