account_usage

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

With no annotations, the description must carry the burden of behavioral disclosure. It implicitly indicates a read-only operation by describing credit usage remaining balance, but it does not explicitly state the operation is non-mutating or mention potential limitations (e.g., rate limits). The description is adequate for a simple query tool but leaves some behavioral aspects unstated.

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 description is two sentences, front-loaded with the tool's purpose and immediately followed by explicit usage conditions. Every word earns its place—no repetition or filler.

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 zero-parameter tool with no output schema, the description is fully sufficient. It covers what the tool provides (credit usage and remaining balance) and when to invoke it, making it complete for an agent to select and use without further clarification.

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 is empty (0 parameters), so the baseline is 4. The description adds no parameter-specific details because none exist; it correctly describes the tool as having no inputs, so no additional semantic value is needed.

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 clearly states the tool reports 'this API key's credit usage and remaining balance for the month,' which is specific and distinguishes it from the sports-related sibling tools. Though it lacks an explicit verb, the intent (returning account usage) is unambiguous.

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?

Explicit when-to-use guidance is provided: 'Use it when a call has been refused with a 402, or when the user asks how much of their quota is left.' This gives clear context and directly instructs the agent on appropriate invocation scenarios.

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