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

With no annotations, the description carries the full behavioral burden. It usefully discloses a commercial/access constraint ('5 free trial calls per signed wallet'), which is genuine context an agent needs. However it says nothing about what happens past the trial, unit expectations, or the return format.

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?

A single front-loaded sentence states the operation and its inputs immediately, followed by the trial-call note. Nothing is padded, though the emoji pricing tag is presentation rather than instruction.

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?

With no output schema, no annotations, zero required parameters and 0% schema description coverage, the description should explain return value, units and payment semantics. It does not, leaving an agent unable to predict the response shape or the consequence of omitting coordinates.

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% and all six parameters are typed as strings with no descriptions. The description merely re-lists the coordinate names (x1,y1,z1,x2,y2,z2) without clarifying units, numeric formatting, or why coordinates are strings rather than numbers, so it does not compensate for the coverage gap.

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 ('Computes the Euclidean distance between two 3D points') and enumerates the exact inputs (x1,y1,z1,x2,y2,z2). The '3D' qualifier cleanly separates it from siblings like x402-distance2d, x402-manhattan-distance and x402-geo-distance without needing to open any schema.

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 statement of when to pick this over x402-distance2d, x402-manhattan-distance or x402-chebyshev-distance; the reader must infer the distinction from the tool name alone. Naming the coordinate inputs hints at usage but provides no conditions or exclusions.

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