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

With no annotations, the description carries the full behavioral burden. It does add one real behavioral fact — 'Free.', i.e. the call costs no credits — and scopes the result to the authenticated user, which are valuable disclosures. It does not address auth failure behavior, whether the period boundary is timezone-dependent, or units of the balance, so the disclosure is only partial.

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?

A single sentence that front-loads the return payload, with the cost note last. No filler, no restatement of the title.

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?

No output schema exists, so the description must carry the return shape — and it does, naming all three returned values. It falls slightly short for a billing-oriented tool by omitting units, whether the balance can go negative, and the reset semantics of the period.

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 takes zero parameters, so there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly says nothing about inputs, which matches the empty schema.

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?

Names a specific verb+resource ('Return the authenticated user's current credit balance') and enumerates exactly which values come back (balance, monthly allocation, credits used this period). It doesn't explicitly contrast itself with adjacent cost/usage siblings like get_usage_history or get_cost_estimate, so an agent must infer the split, but the purpose itself is unambiguous.

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?

No explicit when-to-use or when-not-to-use statement, and no sibling is named as an alternative. The trailing 'Free.' implies this is a safe, zero-cost check, which nudges the agent toward calling it before spending actions, but that is inference rather than guidance.

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