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

Annotations already declare readOnlyHint=true and openWorldHint=false, and the description is consistent with that by stating no funds move. It adds behavioral context annotations cannot carry: a 5-prepaid-credit cost and a production billing requirement — material facts for an agent deciding whether to call it.

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 tight sentences with the core operation front-loaded and no filler. The billing note is compact and clearly separated from the functional statement.

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 one-parameter, read-only, no-output-schema utility, the description covers the operation, the safety profile, and the cost model. The remaining gap is rounding/truncation behavior for inputs with more than 6 decimal places, which materially affects correctness of the output.

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?

Schema description coverage is 0% on the single parameter, so the description must compensate. It does say the input is an 'exact decimal USDC string' (ruling out a numeric type), but adds nothing about accepted formats, precision limits, or how more than 6 decimal places are handled.

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?

Specific verb and resource: 'Convert an exact decimal USDC string to 6-decimal atomic units', with a clarifying negative ('does not transfer funds') that separates it from any payment/movement operation. It is fully unambiguous on its own, though it does not reference related conversion or validation tools among the siblings.

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 'does not transfer funds' clause implies this is for arithmetic/normalization rather than payment, which is useful usage context. However there is no explicit when-to-use vs when-not guidance and no stated preconditions beyond billing.

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