billing.balance

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

Description adds value beyond annotations by specifying returned fields, confirming no charges or holds created, and linking behavior to deploy.run workflow. Aligns with readOnlyHint and idempotentHint.

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?

Three concise sentences: purpose, usage scenarios, and exclusions. Front-loaded with action and resource. No superfluous text.

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?

Completes understanding by tying to deploy.run errors, output fields summary, and clarifying no side effects. Output schema exists for details, description covers usage context.

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?

No parameters, so description doesn't need to explain them. Baseline 4 for 0 params, and description provides useful context about the tool's purpose and output.

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?

Clear verb 'Return' with specific resources (total, held, available USD) and explicit read-only nature. Distinguishes from sibling billing.top_up by stating 'Do not use this to add funds'.

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?

Explicitly states when to call (after HTTP 402 or before deploy.run to check holds) and when not to (to add funds), providing alternative tool (billing.top_up) and retry guidance.

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