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

No annotations are supplied, so the description carries the full burden, and it discloses almost no behavior: no return format, no rounding or precision policy, no error behavior for unsupported units. The only genuine behavioral disclosure is the pricing/quota note ('5 free trial calls per signed wallet'), which is useful but does not cover correctness-critical behavior.

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 compact sentences, front-loaded with the purpose and unit list, followed by the parameter instruction. The trial-call emoji line is minor promotional noise but does carry pricing information, so little is truly wasted.

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 3-parameter tool with no annotations, no output schema, and zero schema descriptions, the definition leaves the agent guessing the critical detail: the exact unit tokens to pass. It should specify accepted unit spellings and whether the result is a number or object.

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 there are no enums, so the description must compensate. It only restates the three parameter names; it does not say whether units accept abbreviations ('km') or full words ('kilometers'), whether matching is case-sensitive, or that 'value' is typed as a string rather than a number.

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 ('Convert a length value') and enumerates all eight supported units, so the agent knows exactly what the tool does. However, it gives no hint as to how it differs from the many sibling single-pair converters (x402-cm-to-inches, x402-feet-to-meters, x402-km-to-miles) or the generic x402-units-convert.

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 value and from/to units' tells the agent how to fill the call, not when to choose this tool over the specialized conversion siblings. There is no exclusion, prerequisite, or alternative named, leaving routing entirely to inference.

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