check_balance

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

Annotations already declare readOnly, idempotent, etc. The description adds concrete error-handling behavior ('returns CREDENTIAL_MISSING error with how-to-fix steps') and return structure, providing context beyond 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 very concise with no redundant words. It front-loads the main purpose, then lists preconditions, usage guidance, and return format efficiently.

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?

Given zero parameters and no output schema, the description covers everything needed: purpose, preconditions, error handling, return fields, and when to use. It is fully complete for this tool.

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?

There are no parameters, so schema coverage is 100%. The baseline for zero parameters is 4, and the description adds no extra param info (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 specifies the verb 'Check' and the resources 'USDC balance, KYC tier, and account info'. It distinguishes itself from siblings like 'call_service' and 'check_tax' by focusing on checking account details before a payment.

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 states to use BEFORE call_service to confirm sufficient funds, especially before a long batch. It also mentions the necessary precondition (env var set). It lacks explicit when-not guidance but is clear enough for the intended use.

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