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

With no annotations, the description carries the full burden, and it omits everything behavioral: no statement of accepted input format (comma-separated numbers vs JSON array), no minimum dataset size, no behavior on ties or non-numeric input, and no indication of what the return payload looks like beyond 'the three quartiles'.

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 sentences, front-loaded with the operation and its outputs. Minor waste in restating the tool name ('Quartile: Calculate quartiles') and in the trailing 'returns the three quartiles', which repeats the Q1/Q2/Q3 enumeration.

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 ambiguous two-parameter input contract, the description is too thin: an agent cannot confidently format input or know which of the two string parameters to use. Nothing beyond the bare computation is covered.

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 schema technically has 100% description coverage, but both descriptions are content-free ('Data to process' / 'Values to process'), leaving two seemingly redundant string parameters with no way to tell them apart. The description says only 'Provide values', which does not resolve which parameter to populate nor the expected encoding, so it fails to compensate for the vacuous schema text.

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 names a specific verb+resource (calculate quartiles) and enumerates the outputs (Q1, Q2 median, Q3), which is enough to distinguish it from a plain mean or median call. It does not, however, point at the closely related siblings (x402-median, x402-iqr, x402-decile, x402-percentile) that an agent must choose between.

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 when-to-use guidance, no prerequisites, and no mention of alternatives, despite the sibling list containing x402-median, x402-iqr, x402-interquartile-mean, x402-decile and x402-percentile. The agent is left to infer that this is the tool for full five-number-style spread analysis.

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