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

With no annotations supplied, the description does carry the full behavioral burden, and it does disclose a commercial trait the schema cannot: five free trial calls per signed wallet, implying a metered/auth-gated service. It says nothing about the response shape, error behavior when the array is empty, or how the 'values' input is actually encoded.

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 core definition is front-loaded in one tight sentence, then the input hint and the pricing note. The emoji-laden trial-call boilerplate is incidental noise but short enough not to obscure the meaning.

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 trivial single-parameter statistic with no output schema, the description covers the computation and a payment caveat, which is roughly enough. The one thing an agent genuinely needs — the concrete input encoding for 'values' — is missing, and the description contradicts the schema's string type.

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% for the single parameter, so the description must compensate and it largely fails: it says 'values array' while the schema declares a bare string with no format, delimiter, or numeric-type guidance. That mismatch leaves the agent unsure whether to send a JSON array, a CSV string, or something else.

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 ('Calculate the statistical range of a dataset') and even defines the computation as maximum minus minimum, which distinguishes it in substance from the many sibling stat tools. It never names the close siblings (x402-range-stat, x402-range-statistic, x402-midrange, x402-iqr), so an agent must infer which one to pick.

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?

'Provide values array' is an input reminder rather than usage guidance. There is no statement of when this tool is preferable to the near-identical siblings such as x402-range-stat or x402-range-statistic, nor any prerequisite or exclusion.

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