account_usage

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

With no annotations provided, the description carries full responsibility. It discloses a key behavioral outcome (402 payment_required when limits are exhausted) and the return shape. However, it does not explicitly state that the call is read-only and has no side effects, which would be valuable given the absence of annotations. The description is helpful but not exhaustive.

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 compact and front-loaded with the purpose, followed by a concrete usage tip and a list of return keys. Every sentence earns its place, with no redundancy or fluff. It is optimally sized for quick comprehension.

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, read-only usage check with no output schema, the description provides the essential information: what it returns, when to call it, and what a failure (402) means. Nothing an agent needs to invoke it correctly is missing, especially given the simplicity of the 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 has zero parameters and the schema is empty, so there is no parameter semantics to add. The baseline for 0-parameter tools is 4, and the description correctly adds no parameter information while providing context about the expected return dictionary, which is the relevant semantic content.

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 resource and action: 'Current-month usage and prepaid balance for this API key.' It clearly distinguishes from all sibling tools, none of which cover usage or billing. The phrasing is concrete and unambiguous, leaving no need to infer the tool's role.

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 an explicit when-to-use cue: 'Call this before a bulk loop.' It also explains the meaning of the 402 error, which helps the agent decide whether to proceed. However, it doesn't mention alternatives or when not to use it, though no sibling tool serves a similar purpose, so that omission is minor.

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