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

With no annotations, the description carries the full burden of behavioral disclosure. It discloses the formula but omits the return format, required input type, and handling of invalid or empty datasets. More importantly, it instructs the agent to 'Provide values array' while the input schema declares zero parameters, leaving invocation behavior ambiguous.

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-loaded, opening with the tool's purpose and formula. The 'Provide values array' sentence is terse and grammatically awkward, but overall the description contains no filler and earns its two sentences.

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 simple statistical calculator, the core formula is helpful, but the tool is incomplete as specified: the described input cannot be passed through an empty schema, the return value is not described, and edge cases like non-numeric or empty arrays are unaddressed. The schema-description mismatch is a critical gap.

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 description introduces a 'values array' input that does not exist in the schema, which has an empty properties object. This is actively misleading: the schema offers no place to pass the array, and the description gives no type, format, or cardinality details for how the array should be supplied.

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 uses a specific verb ('Calculate') and resource ('trimean of a dataset'), then precisely defines the computation as the weighted average of the median and the two quartiles. This distinguishes it from nearby statistical siblings like median, quartile, trimmed-mean, and interquartile-mean.

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?

The description gives no guidance about when to choose trimean over related tools such as x402-median, x402-quartile, x402-trimmed-mean, or x402-interquartile-mean. It only states what the tool computes and says to provide a values array, with no context, exclusions, or alternatives.

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