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

With no annotations, the description carries the full burden; it usefully discloses the computation method and the pricing/rate limit ('5 free trial calls per signed wallet'), which is real behavioral context. However, it never states what the response contains (a single number? quartiles too?) or what happens on insufficient/invalid data, which matters for a tool with zero annotation coverage.

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?

One front-loaded sentence giving the definition plus a short input hint and a pricing note; nothing is padded or redundant. The trial-call banner is boilerplate but brief.

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 single-input calculator with no output schema and no annotations, the mathematical definition is adequately complete conceptually, but the input encoding and the shape of the result are left for the agent to guess, which is a meaningful gap given nothing else describes them.

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?

There is only one parameter so the burden is small, and 'Provide values array' does tell the agent what belongs in it. But the schema types 'values' as a string while the description says 'array', leaving the actual encoding (comma-separated, JSON string, whitespace-separated) unresolved at 0% schema coverage.

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 gives a specific verb ('Calculate') and resource ('trimean') and then defines it as the weighted average of the median and the two quartiles, which distinguishes it from nearby siblings like x402-median, x402-quartile, x402-midhinge and x402-trimmed-mean. It doesn't name a sibling explicitly, so it falls just 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?

'Provide values array' is an input instruction, not usage guidance. There is no statement of when to prefer trimean over median, mean, or the other central-tendency siblings, and no prerequisites or exclusions are given.

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