whoami

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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false. The description adds real value beyond that by stating 'Costs no credits' and by enumerating the returned fields, which the readOnly annotation alone would not convey.

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 sentences, front-loaded with what the tool reveals, followed by cost and then the invocation trigger. Every clause carries information; nothing is wasted.

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 enumerates the return payload (plan, auth, scopes, readable apps, credit balance), which is exactly what an agent needs. No annotations or schema gaps are left uncovered.

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 takes zero parameters, which sets the baseline at 4; there are no argument semantics to clarify. The description's enumeration of return fields compensates in spirit but is not a parameter concern.

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, unambiguous purpose—identity/auth introspection for the current key or session—and enumerates what it reveals (plan, auth method, scopes, readable apps, credit balance). No sibling tool does this, so it is clearly distinguishable from the rest of the catalog.

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?

It gives an explicit trigger: 'Call it when a call was refused for plan, scope or app reasons.' That is a concrete condition that selects this tool over any other, and for a zero-param singleton diagnostic there is no meaningful alternative to name.

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