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

With no annotations, the description carries the full burden and usefully discloses the per-call cost and x402 payment model, which is behavioral context beyond the schema. However, it says nothing about which operation is selected when parameters are omitted, what errors occur on invalid combinations, or what the return looks like.

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 sentences with no waste: the operations are front-loaded, followed by the pricing note. The multi-operation first sentence is a bit dense but still efficient.

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 five-parameter tool with no required fields, no annotations, and no output schema, the description is too thin. It does not resolve which parameters correspond to which of the three calculations, leaving a critical ambiguity that could cause incorrect invocation.

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 100%, so the schema already documents each parameter (Base value, New value, Old value, Percent, paymentProof). The description does not add mapping details to clarify parameter grouping for each calculation, so the baseline of 3 is appropriate.

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 names three specific percent-related calculations (percent change, X percent of Y, reverse percent change), which is enough for an agent to know what the tool does. It doesn't need sibling differentiation because no other sibling performs percent math, but the phrasing is a dense list rather than a clean verb+resource statement.

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?

There is no guidance on which parameters to supply for which of the three operations, and all five parameters are optional. An agent must guess whether to pass from/to, percent/of, or another combination. No alternatives or exclusions are mentioned.

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