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

readOnlyHint=true already declares this as a safe read, so the description's 'Look up' adds no safety information. It contributes the underlying endpoint (GET /v2/user/resolve/{client_user_id}) and the ownership semantics of the id, but says nothing about behavior when the id is unresolved or about rate limits.

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?

Two compact sentences with the purpose front-loaded and the identifying key emphasized by parenthetical. Nothing is padded or redundant.

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 single-parameter read tool with annotations carrying the safety profile and no output schema, the definition covers what an agent needs to select and invoke it. The only minor gap is not hinting at the returned user payload, which is acceptable given there is no output schema.

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 single parameter, so the schema already documents client_user_id. The description's restatement '(the stable id you assigned)' mirrors the schema text and adds no new syntax or format detail, matching the baseline-3 case where the schema does the work.

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), resource (Vital user), and the identifying key (client_user_id). It implicitly distinguishes itself from the sibling vital_get_user by emphasizing 'your own client_user_id', but never names the alternative or makes the distinction explicit.

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 parenthetical '(the stable id you assigned)' implies you use this when you hold a client_user_id, but there is no explicit when/when-not guidance and no routing to vital_get_user or vital_list_users. Usage is implied rather than stated.

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