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

While annotations already provide the 'readOnlyHint: true', the description adds crucial behavioral detail by listing the specific metrics returned (credits, usage, rate limit). This provides valuable context about the nature of the data returned.

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?

The definition is concise, consisting of a single sentence that contains all necessary information without waste or fluff.

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 there are no parameters and an output schema exists, the description successfully summarizes the intended output content. It is complete for a usage-reporting 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?

With zero parameters, the description is perfectly sized, and the 100% coverage means it receives the baseline score of 4 for parameter utility.

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 is highly specific, stating that the tool returns 'credits, usage, and rate limit' regarding the 'caller's API' usage. This clearly defines the resource and action.

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 usage is implied by the function's title and description—monitoring limits. Since no competing tools are mentioned within the description text, it falls to a general implied usage.

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