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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false. The description adds useful context beyond annotations: it lists the returned fields and names the required auth scope, which is genuinely helpful for an agent deciding whether it can call this tool.

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 short sentences, no wasted words, and the core purpose is front-loaded before the auth-scope note. It is appropriately sized for a zero-parameter read tool.

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?

Given that the tool has no parameters, an output schema, and safety annotations, the description covers the essentials: what it returns and the required scope. The only minor gap is that it does not compare itself to related account or identity tools.

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, so there is no parameter semantics burden. The description does not need to explain inputs and correctly focuses on output and auth scope, though it could note that no inputs are required.

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 clearly states the resource: it returns the identity associated with the credential (email, plan, credit balance). That is a specific and useful resource, though it does not explicitly distinguish itself from related account-ish siblings such as capabilities_list or identity_* tools.

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 a prerequisite ('Needs the read scope') but does not state when to prefer this tool over alternatives or when not to use it. For a simple identity endpoint the implied usage is fairly obvious, but no explicit guidance or exclusions are provided.

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