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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds meaningful behavioral context beyond that: the profile is public-only and email is conditionally present ('appears only when the user made it public'), which warns the agent about potentially missing fields. It doesn't discuss rate limits or auth, keeping it short of a 5.

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?

One front-loaded sentence covering what is fetched plus the email caveat, followed by a routing sentence. Zero filler and no repetition of structured data.

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?

A single-parameter read tool with an output schema, so return-value description is unnecessary. Purpose, scope (public), the email caveat, and sibling routing cover everything needed to invoke it 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?

Schema description coverage is 100% and the single `username` param is documented in the schema, so the schema does the heavy lifting. The description references `username` but adds no format, casing, or URL-vs-handle guidance. Baseline 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?

States a specific verb (Fetch) and resource (public GitHub user profile and user-published social links) keyed by `username`. It explicitly differentiates itself from github_user_repos, github_user_followers, and github_search_users, so an agent can select it without inspecting sibling schemas.

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?

Names the exact alternatives and the conditions under which to prefer them: related lists via github_user_repos / github_user_followers, account discovery via github_search_users. This is explicit when/when-not routing rather than implied usage.

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