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

The readOnlyHint already signals a safe read operation, and the description adds meaningful context beyond it: rounding is cash-only, applied to the total rather than each item, happens after tax, and is not free money for retailers. It also warns that floating-point money handling is risky. No contradiction with 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 front-loaded with the core computation and then gives expected numeric behavior and a structured 'WHY DELEGATE THIS' section. The ownership/direct-call sentence is slightly tangential, but overall the text is readable, organized, and each major sentence contributes useful context.

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?

The description conveys the tool's purpose and an expected magnitude for always-up ('about 2 cents a sale'), but it does not specify the exact return format or units, the default rounding rule, or what happens when taxRatePercent is omitted. With no output schema, these details would help make invocation fully unambiguous.

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 only 33%, so the description must compensate, but it only partially does. It mentions price lists and 'always-up,' but does not explain the symmetric/always-down/none rule semantics, the default rule, or the meaning and optionality of taxRatePercent. The schema alone does not document these either.

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 first sentence names a precise computation: 'Compute the mean rounding delta per cash transaction across a price list.' This gives a specific verb and resource and clearly separates this tool from a sibling like round_cash_total, which would compute a rounded cash total rather than a mean impact.

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 gives a concrete use case: it answers whether rounding makes retailers money with arithmetic instead of a guess. It also tells the caller to pass always-up to quantify the 'round everything up' policy. It does not explicitly name alternatives or exclusions, but the context is clear enough for selection.

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