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

With no annotations present, the description must fully disclose behavioral traits. It notes 'Auth required,' which is a meaningful behavioral constraint, and explains the balance calculation. However, it omits other traits that could be relevant, such as read-only nature, potential latency, and what happens on insufficient permissions. It's adequate but not rich in disclosure.

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 exceptionally concise: two short sentences, each earning its place. The first sentence defines the resource with a clear formula, and the second highlights authentication. No fluff, front-loaded with the most important information.

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 the absence of an output schema, the description should have explained what the response contains (e.g., a numeric balance, currency, decimal places). It does not. The tool is simple enough that the omission might be acceptable, but from a completeness standpoint, knowing the return format would be essential for programmatic use. At minimum, it falls short of fully documenting a zero-parameter call.

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 100% (vacuously). The rubric prescribes a baseline of 4 for zero parameters, and the description does not need to compensate for missing parameter details. There are no undocumented parameters to worry about.

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 states the tool returns the prepaid fee balance, defined precisely as 'settled credits minus fee debits.' This specific verb-resource pairing unambiguously distinguishes it from other tools like check_spend or topup_balance, which could otherwise be confused for balance-related operations.

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 provides no guidance on when to use this tool versus alternatives like check_spend, get_me, or list_tokens. It neither mentions scenarios where this tool is appropriate nor excludes cases better served by siblings. The only hint is the formula, which implies a financial balance context, but no explicit or even implicit when-to-use advice is given.

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