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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower; the description still adds meaningful context by stating it does not consume credits and requires OAuth or API key authentication. That auth requirement is not derivable from the annotations and directly affects whether an agent can call it.

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?

Three sentences, zero waste, and the return contents are front-loaded ahead of the operational caveats. Each sentence carries distinct information: what it returns, its cost/auth profile, and when to invoke it.

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 responsibly enumerates the returned fields (identity, product scope, credit balances) so the agent knows what it gets back. Auth requirements and the credit-check use case round out everything needed to call a zero-parameter read tool.

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 (100% schema coverage), so there is nothing for the description to disambiguate. It neither needs to nor attempts to explain parameter syntax, which matches the baseline for a parameterless tool.

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 verb and resource ('Returns authenticated user identity') and enumerates the exact payload: identity, product scope, and credit balances. It is unambiguously distinct from the job/generation/voice siblings, which concern media work rather than account state.

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 a concrete usage trigger: 'Check credit balance before creating jobs or generations,' which maps this tool into a real workflow alongside create_files_job and generate_x_audio. It stops short of naming alternatives or stating when not to call it, so it is clear context without explicit exclusions.

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