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

With no annotations, the description carries the full burden. It does disclose a useful behavioral trait that structured fields cannot: a paywall with 5 free trial calls per signed wallet. However it says nothing about what the computation returns, how empty or single-element input is handled, or what errors look 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 short clauses, front-loaded with the operation and followed by the pricing note. Nothing is padded, though the pricing emoji adds little for an agent parsing text.

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 tool with no annotations, no output schema, and an undocumented string parameter, the definition is incomplete. The single critical gap, the expected string encoding of 'values', is left entirely unaddressed.

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 coverage is 0% for the single 'values' parameter, so the description must compensate and does not. It never says whether values is a comma-separated list, a JSON array string, or space-delimited numbers, which is exactly the information needed to invoke the tool correctly.

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?

"Sample Mean: Mean of sample" restates the tool name and title without adding scope. It does not distinguish this from the many sibling statistics tools such as x402-mean-of, x402-population-mean, or x402-trimmed-mean, leaving the agent to infer the distinction from the name alone.

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 statement of when to use this versus the population-mean or generic mean siblings, and no preconditions. The only conditional text ('5 free trial calls per signed wallet') is about billing, not about when the tool is the right choice.

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