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

Annotations already declare readOnlyHint/openWorldHint/destructiveHint=false, and the description adds real value beyond them: which fields are omitted (permissions, admin flags, credentials, private fields) and the one-page pagination default. The 'untrusted customer content' warning is boilerplate that seems aimed at message-text tools rather than a user directory, which weakens the signal.

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?

Compact and front-loaded with the purpose, endpoint and read-only status in the first few clauses. The untrusted-content sentence is the one element that doesn't clearly earn its place for a user-listing tool.

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?

With no output schema, the description usefully names the returned fields and states which are stripped, plus the paging behavior. But it leaves the entire filter/pagination parameter surface undescribed, so an agent can't confidently build a filtered or paginated call.

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?

All four parameters (page, page_size, email, external_user_id) have 0% schema description coverage, so the description carries the full burden and fails: it never says these act as filters, never explains the page/page_size defaults or the 100 max, and never confirms email/external_user_id are exact-match lookups.

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 ('look up') and resource ('user names, emails and external IDs') with the endpoint GET /users. It differentiates from list-only siblings implicitly but never contrasts with textrequest_get_user, so single-vs-list selection is left to inference.

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?

'for assignment/context' hints at the intended use case, but there is no explicit statement of when to call this instead of textrequest_get_user, nor any note that the optional email/external_user_id params narrow the list.

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