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

With no annotations, the description carries the full behavioral burden, but it does disclose a genuinely useful edge-case behavior: it returns zeros when the standard deviation is zero. It does not disclose input parsing behavior, error handling, or rate limits beyond the trial note, leaving gaps for a computation tool.

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?

A single front-loaded sentence covering operation, method, and edge case, followed by a short promotional tail. The free-trial emoji clause is extraneous to tool selection but does not bury the substance.

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 one-parameter math utility with no output schema, the core behavior is described adequately. However, the unresolved string-vs-array input format and absent usage context leave real gaps an agent would need filled before invoking it correctly.

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 'values' parameter, so the description must compensate. It calls it 'a values array' while the schema types it as a string, and never explains the expected encoding (JSON array, comma-separated, etc.), creating ambiguity rather than resolving it.

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 ('converts a values array to z-scores') and adds a precise methodological qualifier ('using the population standard deviation'), which is meaningful given the many statistics siblings. It does not explicitly differentiate itself from the non-array sibling x402-zscore or from x402-standardize-array, so it stops short of a 5.

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 alternatives such as x402-zscore or x402-standardize-array, and no prerequisites or context. The only 'when' guidance is the payment note about free trial calls, which is not usage selection guidance.

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