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

No annotations are provided, so the description fully carries the burden. It discloses read-only behavior, no state modification, no payment sending, no upstream API calls, and the requirement for a valid API key. This is comprehensive for a zero-parameter endpoint.

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 concise, front-loaded with 'Read-only', and every sentence serves a purpose: what it returns, auth requirement, use cases, and exclusions. No redundant or vague language.

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 zero-parameter, no-output-schema tool, the description is remarkably complete: it details return values (balance, spending, request count), units, authentication, usage guidance, and explicitly states what it does not do. The context is fully covered.

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 schema coverage is trivially 100%. The description correctly omits parameter details as none exist; baseline 4 for zero-parameter tools is appropriate.

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?

Clearly states it returns current balance, lifetime spending, and request count with specific units (microdollars and USD). Distinct from siblings by explicitly being read-only and focusing on account/usage information rather than executing calls or queries.

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 advises using before apihub_call or apihub_call_external to confirm sufficient funds and periodically for audits. Also names apihub_topup as the alternative for changing balance, providing clear when-to-use versus alternatives.

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