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

With no annotations, the description must carry behavioral disclosure; 'Convert between distance units' at least establishes this is a pure conversion operation. It does not disclose supported unit names, direction semantics (from/to), output format, or error behavior, so the behavioral picture is thin.

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 a single short sentence and the functional statement is front-loaded. The 'Distance:' label is slightly redundant before the sentence 'Convert between distance units' but it does not add significant bulk.

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 three-parameter conversion tool, the description is minimally adequate: an agent can infer the basic call pattern. However, there is no output schema and no list of accepted distance units or input value conventions, which are meaningful gaps for an agent to invoke the tool correctly without further examples.

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 descriptions are generic placeholders ('To to process', 'From to process'), so the description adds real meaning by indicating that 'to' and 'from' refer to distance units and 'value' is the quantity being converted. It still leaves unit spelling and value format unspecified, but it meaningfully complements the schema.

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 operation (convert) and a resource (distance units), so an agent can understand the core function. It is somewhat distinguishable from siblings like x402-distance2d or x402-geo-distance because it targets unit conversion, but it does not explicitly differentiate itself from other conversion tools such as x402-units-convert or x402-length.

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 tool's use is implied: when a distance-unit conversion is needed, this is the tool. However, the description gives no explicit guidance about when not to use it, no prerequisites, and no mention of alternatives among the many sibling conversion tools.

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