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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It explicitly reveals a non-obvious trait: calling this tool does not spend credits, which implies a read-only, non-consuming operation. It does not cover return format or authentication requirements, but for a 0-parameter read tool this covers the most important behavior.

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 short sentences with no filler. The primary action is front-loaded, and the cost-related note is a single compact clause. Every word earns its place.

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 simple, parameterless read operation with no output schema, the description fully explains what the tool does, the account scope, and the key cost behavior. Nothing essential for an agent to invoke it correctly 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 tool has zero parameters, so the baseline is 4 as per the rubric. The description adds no parameter-level meaning, but none is needed because the schema is empty and there is nothing to document.

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 precise action ('Check'), a specific resource ('remaining pre-paid API credit balance'), and the scope ('connected NumberBroom account'). It is clearly distinguishable from the only sibling, verify_phone_number, which obviously performs a different operation.

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 phrase 'Free to call — does not spend credits' clearly signals when to use this tool (when balance info is needed without consuming credits), but it does not explicitly mention an alternative or state a 'when not to use' condition. The context is clear enough, though exclusion guidance is absent.

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