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

Annotations already declare readOnly/idempotent/non-destructive, so the safety bar is low. The description adds real behavioral context beyond that: output varies by credential type ('with a hosted token' surfaces token name and expiry), which is a conditional behavior an agent cannot infer from annotations or the empty schema.

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 the returned fields and closing with the usage trigger. The field enumeration is dense but each item (plan values, token expiry) earns its place by telling the agent what it will get.

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?

An output schema exists, so return format is already covered, and the tool takes no params. For a read-only identity check, the description supplies everything an agent needs: what it does, what it returns, and when to reach for it.

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?

Zero parameters, so the baseline is 4; there is nothing to document. The description does not need to add parameter meaning and correctly does not invent any.

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?

Names the specific operation (identify the authenticated account) and enumerates exactly what it returns: email, plan, free-run quota, and hosted-token name/expiry. This is fully distinguishable from every sibling (catalog.*, execution.*, stream.*, etc.), none of which touch identity or credentials.

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?

Gives concrete triggers: 'Call this first when setup guidance appears' and 'to check which credential a session uses.' That is clear when-to-use guidance. It stops short of explicit when-not or named alternatives, but no sibling competes for this role, so the guidance is effectively complete.

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