Credit balance

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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the agent knows this is a safe read. The description adds what data is returned (balance, spent credits, recent calls) but does not disclose additional behavioral traits beyond the annotations. It is consistent with annotations and adds some value, but not much beyond what annotations cover.

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 a single efficient sentence. It front-loads the primary purpose ('Return the account credit balance') followed by supplementary details and a usage hint. No wasted words.

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 tool, the description is complete enough. It tells the agent what it returns and when to use it. Minor ambiguity about 'recent priced calls' exists, but it doesn't hinder invocation. The lack of an output schema is acceptable given the simplicity.

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. There is no need for the description to explain parameters. It correctly implies no inputs are required.

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 verb ('Return'), a clear resource ('account credit balance'), and specifies exactly what is returned: the balance, credits spent on calls, and recent priced calls. It also includes a usage hint ('Check before kicking off paid generation') that clarifies its role. This distinguishes it from siblings like buy_credits (purchase) and billing_status (likely broader billing info).

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 explicitly tells the agent when to use this tool: 'Check before kicking off paid generation.' This is clear contextual guidance. It doesn't name alternative tools or when not to use it, but the purpose is obvious and the hint is actionable.

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