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

readOnlyHint=true already tells the agent this is a safe, non-mutating read, so the bar is lower. The description adds only the field inventory and the dual lookup key; it says nothing about auth requirements, rate limits, or error behavior when the user is not found.

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 tight sentences, front-loaded with the action, followed by the return-field inventory and the underlying endpoint. Zero 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?

With no output schema, the description carries the burden of saying what comes back, and it does list profile, role, tags, sign-up fields, UTMs and last login. It is slightly incomplete on the include_suspended interaction and lookup failure behavior, but otherwise sufficient for a simple read tool.

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%, so both parameters — including the suspended-user flag — are already fully documented in the schema. The description's 'by id or email' merely restates the schema and adds no syntax or format detail, so baseline 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?

States a specific verb and resource ('Fetch one user') plus the lookup keys (id or email), which cleanly separates it from the sibling list_users and from create/update_user. An agent can tell exactly what it gets back without opening the schema.

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?

Usage is only implied: 'one user' signals single-record retrieval when you already hold an identifier, but no sibling is named and no when-not condition is given (e.g. use list_users for broad queries). Minimum viable, no routing help.

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