get_user_by_username

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

No annotations are provided, so the description carries the full burden. It discloses the return payload (name, bio, location, repo/follower counts), the 404 error case for nonexistent or Enterprise Managed Users, and links to official docs. This goes beyond minimal by specifying error behavior.

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 three sentences, front-loaded with the primary action, then return fields, then error behavior. No redundant language or filler.

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 single-parameter lookup with no output schema, the description covers purpose, return fields, error case, and documentation link. It is sufficiently complete for an agent to invoke correctly.

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 already fully describes the single 'username' parameter with a clear description. The tool description adds little beyond echoing 'login (username)', so it meets the baseline for high schema coverage.

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 uses a specific verb 'Get' with a resource 'GitHub user' and specifies the lookup method 'by their login (username)'. It clarifies the public scope and lists return fields, distinguishing it from similar tools like get_authenticated_user or search_users.

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?

It clearly indicates this is for fetching public profile data by username, implying use when you have an exact login. It does not explicitly name alternatives or exclusions, but the context is unambiguous. The 404 note also informs when the user might not be found.

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