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

No annotations are supplied, so the description carries the full behavioral burden. It discloses a commercial trait (free trial calls per signed wallet), which is genuinely useful, but says nothing about what is returned, units, precision, or what happens when inputs are omitted. The schema's string-typed parameters and zero required fields are left unexplained.

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?

Very short and front-loaded: the operation is stated first, then the pricing note. Nothing is padded or redundant. Brevity here reflects under-specification rather than trimming, but the structure itself is clean.

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 mathematical tool with no output schema, no annotations, and 0% parameter documentation, the description should say what the result looks like (a number, units, precision) and how width/height/length are supplied. None of that is present, so an agent calling it correctly is largely guessing.

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% across three parameters. Names (width, height, length) are intuitive, but the description adds no units, no indication that values are strings, and no explanation of the fact that all three are optional and what defaults apply if omitted. With low coverage the description should compensate and does not.

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 resource and quantity: 'Space diagonal of a cuboid', with the tool name reinforcing it. An agent knows exactly what computation this performs. It does not, however, distinguish itself from close siblings like x402-cube-diagonal, x402-cube-space-diagonal, x402-rectangular-diagonal, or x402-distance3d.

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?

No guidance on when to use this versus the several adjacent diagonal/distance tools. The only extra sentence concerns pricing ('5 free trial calls per signed wallet'), not invocation context. The agent must infer selection from the name alone.

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