Get the prepaid account balance

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

The annotations already declare readOnly, idempotent, and non-destructive behavior, and the description does not contradict them. The description adds context about the consequence of insufficient balance, which is helpful but not required given the annotations.

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 long and contains no fluff. Every word adds value: it states the return value, the recommended usage, and the reason for that usage.

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?

The description fully covers the tool's purpose and when to use it. While it doesn't describe the output format, the simplicity of the operation (returning a balance) makes this omission acceptable, and the presence of an output schema (mentioned in context signals) further mitigates the need.

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, so there is nothing to explain. According to the baseline for 0 parameters, a score of 4 is appropriate since the description doesn't add extra parameter-related context (none 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's function with a specific verb ('Returns') and a specific resource ('prepaid balance'). It is easily distinguishable from sibling tools, which focus on DNS, domains, SSL, and other distinct operations.

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 provides explicit usage guidance: 'Check it before any operation that spends credit' and explains the rationale ('an insufficient balance is a common cause of a rejected order'). This tells the agent exactly when to invoke this tool.

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