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

With no annotations, the description carries the full burden, and it does disclose the return semantics ('the value at that decile boundary') plus the 5-free-call wallet-gated pricing. It does not cover edge behavior such as an empty values array, out-of-range decile input, or interpolation method.

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?

Three short sentences, front-loaded with the purpose, then inputs, then return value. The trial-call promo adds length without agent value but is brief enough not to interfere.

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 two-parameter, no-annotation, no-output-schema tool, the description covers inputs and the return value adequately. It falls short on the string-serialization format for the array and on input validation behavior.

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% and both parameters are typed as bare strings, so the description's clarifications that 'values' is an array and 'decile' is 1-10 add real meaning beyond the schema. However, it never explains the encoding expected for the string-typed array (comma-separated vs JSON), leaving a critical ambiguity.

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 opens with a specific verb and resource ('Calculate a decile of a dataset') and states the inputs and the returned value. It is clearly distinguishable from siblings like x402-quartile or x402-percentile, though it never explicitly positions itself against them.

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?

Usage is implied by the verb and parameter list but there is no when-to-use guidance, no exclusions, and no pointer to the closely related percentile/quartile tools an agent might confuse it with. The agent must infer the context itself.

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