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

Annotations already declare readOnly, idempotent, non-destructive, closed-world semantics, so the safety profile is covered. The description still adds real value beyond that by defining the unit ('1000 millicredits equal one credit') and the precise semantic of 'spendable' (excluding credits reserved by in-progress forecasts), which prevents misreading the returned number.

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?

Two short sentences, front-loaded with the scope qualifier before the unit definition. Every clause earns its place: the exclusion rule and the millicredit conversion are both needed to interpret the result.

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 zero-parameter read tool with a declared output schema, nothing further is required: safety is covered by annotations, return shape by the output schema, and the description supplies the unit and exclusion semantics an agent needs to interpret the number correctly.

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 the baseline is 4; there is nothing parameter-related left to document. The unit explanation in the description pertains to the return value rather than inputs.

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?

States a specific verb and resource ('Return the account's spendable credit balance') and sharpens the scope with 'excluding credits reserved by in-progress forecasts'. It does not explicitly name or differentiate itself from the sibling get_usage, so an agent must infer the boundary between balance and usage.

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 statement or named alternatives (e.g., get_usage vs. get_balance) are given. Usage is implied by the purpose and the zero-parameter, no-argument nature of the call, which makes selection largely self-evident but not spelled out.

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