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

Annotations already indicate readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds meaningful behavioral context beyond annotations by specifying exactly what will be reported (roles, scopes, tools), which is especially valuable given there is no output schema to convey return contents.

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?

A single, well-structured sentence that front-loads the core action ('Show who is logged in on this session') and then appends the key detail fields. Every word earns its place; there is no filler or redundant restating of the tool name.

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, zero-parameter, read-only whoami tool, the description is complete: it states the identity scope (current session), the output categories (roles, scopes, usable tools), and annotations cover side-effect safety. There is no output schema, but the description sufficiently describes what the agent can expect to learn from the 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?

The tool has zero parameters, so parameter semantics are trivially complete. The baseline for 0-parameter tools is 4, and the description does not need to add anything about parameters since none exist and schema coverage is 100%.

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 uses a specific verb ('Show') with a clear resource ('who is logged in on this session') and enumerates the exact information returned: roles, scopes, and usable tools. This differentiates it from sibling auth tools like login and logout by focusing on the current session rather than authentication actions.

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 implies when to use the tool: whenever the agent needs to know the current user's identity, permissions, roles, or available tools. It does not explicitly name alternatives or exclusions, but for a zero-parameter, read-only introspection tool with no closely overlapping siblings, the context is sufficiently clear.

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