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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the trailing 'Read-only' largely restates structured data. The description does add value annotations cannot: it discloses the returned fields and the 'when available' conditionality on plan usage, which tells the agent to expect partial results.

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?

Front-loaded with the triggering situation, then the return payload. The standalone 'Read-only' sentence is redundant given readOnlyHint=true and is the one piece that does not earn its space.

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 parameters, no output schema and full annotation coverage, the definition supplies what an agent needs: when to call it and what it yields. The only residual gap is that 'surface' is unexplained jargon an agent may not be able to interpret.

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 no parameters and the schema is empty, so there is nothing for the description to disambiguate. Baseline for a zero-parameter tool 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?

Names a concrete operation (retrieve the current authenticated identity) and enumerates exactly what comes back: identity, tier, surface, selected connected account and plan usage. It does not explicitly contrast itself with the only sibling, list_capabilities, so it stops short of a 5.

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 explicit trigger conditions tied to user phrasing ('who they are signed in as', 'which plan they are on', 'which account is selected'), which is strong positive guidance. There are no when-not-to-use conditions or a named alternative, so it is not fully discriminating.

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