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

The annotations already declare readOnlyHint, idempotentHint, and destructiveHint, and the description consistently reinforces this. It adds useful context beyond the annotations by stating it is not separately rate-limited and that it is scoped to the current API key.

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?

Every sentence earns its place: the first states purpose, the second covers safety and rate limiting, the third routes to the sibling tool and lists return fields. It is compact and front-loaded.

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?

For a parameterless read-only tool with no output schema, the description fully covers what the agent needs: what it returns, that it is safe, that it is not separately rate-limited, and how it relates to get_limits. Nothing essential is missing.

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 input schema has zero parameters, so parameter semantics are not a concern. A baseline of 4 is appropriate since the description correctly omits parameter details that do not exist.

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: get current billing period usage vs quota for the API key. It also lists the exact returned fields, which removes ambiguity, and it distinguishes itself from get_limits, its closest sibling.

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 explicitly directs the agent to get_limits for plan ceiling values, which is the main alternative. It could also have clarified when to prefer get_billing_info or other billing siblings, but it gives enough guidance for the core decision.

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