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

readOnlyHint=true already covers the safety profile, and the description consistently describes a read-only GET operation. It adds the endpoint but does not disclose behavior such as what happens when the client_user_id is not found or any rate limits. With annotations carrying the load, a 3 is appropriate.

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 one concise, front-loaded sentence that includes the essential endpoint. Every word earns its place; there is no filler or redundant explanation.

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 one-parameter read-only lookup, the description plus schema and annotations are sufficient for an agent to invoke it correctly. It does not state the return shape, but with no output schema and a straightforward 'look up a Vital user' framing, this is a minor gap.

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 has 100% coverage for the single parameter, and the description essentially repeats the schema's description ('your own stable id for the user'). No additional semantic information is provided, so the parameter-semantics baseline of 3 applies.

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 states a specific verb ('Look up'), the resource ('Vital user'), and the lookup key ('your own client_user_id'). It clearly conveys what the tool does, though it does not explicitly differentiate itself from sibling tools like vital_get_user or vital_list_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?

The description gives clear context for when to use this tool: when you have your own stable client_user_id. It does not explicitly name alternatives or state when not to use it, so it misses the full exclusions that would make it a 5.

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