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

With no annotations, the description carries the full behavioral burden and mostly fails: it does not explain required inputs, accepted data formats, output shape, handling of mismatched lengths, or what wallet signing/payment entails. The free-trial note is the only behavioral context provided.

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 short and front-loads the core operation, which is good. But the second sentence is promotional pricing text rather than functional detail, and the space would have been better spent on the ambiguous parameter pairs.

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 four-parameter statistical tool with no annotations, no output schema, and zero schema description coverage, the definition is substantially incomplete. It does not resolve the most important ambiguity: which of the duplicated input parameters to use.

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 schema has four parameters with 0% description coverage, and the description mentions none of them. Critically, it does not clarify whether yPred/yTrue and actual/predicted are aliases or alternatives, so an agent cannot reliably choose which pair to supply.

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 states a specific operation and resource: 'Compute R² (coefficient of determination).' This is clear enough for an agent to know the tool calculates R-squared. However, it does not distinguish the tool from the nearly identical sibling x402-r-squared, nor does it explain why both exist.

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 when to use this tool versus alternatives such as x402-r-squared, x402-adjusted-r-squared, or error metrics like x402-mean-squared-error. The only additional context is pricing ('5 free trial calls per signed wallet'), which is not usage guidance.

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