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

With no annotations at all, the description carries the full burden of behavioral disclosure. It does reveal one useful non-obvious trait—5 free trial calls per signed wallet, implying a signed-wallet auth requirement and a paywall after the trial—but says nothing about the distance formula, output units (km/miles/meters), or precision assumptions.

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?

It is short and front-loaded, but the brevity comes from under-specification rather than efficiency; "Distance between geo" is an incomplete sentence and the emoji/pricing tail occupies half the text.

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 an 8-parameter, zero-annotation, no-output-schema tool with 0% schema coverage, this is far too thin: coordinate format, unit of result, which parameter set is authoritative, and the calculation method are all absent.

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 coverage is 0% across 8 parameters, so the description must compensate and does not. It never explains the three overlapping coordinate pairs (lat1/lon1+lat2/lon2 vs fromLat/fromLon vs toLat/toLon), which set to use, or the required coordinate format—an agent cannot reliably choose inputs.

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?

"Geo Distance: Distance between geo" restates the tool name without specifying the resource or method—it does not say whether this is great-circle/haversine distance between two lat/lon points or something else, nor distinguish it from siblings like x402-distance, x402-distance2d, x402-chebyshev-distance, or x402-geo-bounding. The only substantive sentence is about billing, not purpose.

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 among the many distance tools in the sibling list. The single sentence on free trial calls is pricing/payment context, not usage guidance.

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