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

No annotations are provided, so the description carries the full burden and does little: it does not state the formula, whether inputs are unit-agnostic, the return type (a number? a string?), or rounding behavior. The one behavioral detail given is commercial — 5 free trial calls per signed wallet — which at least signals an x402 paid endpoint.

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, but a large share of the text is the paywall/trial banner and an emoji rather than the calculation contract. It is under-specified rather than efficient — the length is small because content is missing.

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?

No annotations, no output schema, and zero parameter descriptions leave the agent without units, return format, or input-format expectations for a 3-parameter math tool. A single clause about units and the returned value would have made this adequate.

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?

Three parameters at 0% schema description coverage, with width/height/length typed as strings and unexplained. The description adds nothing about accepted formats, units, or whether the dimensions must be positive numbers; only the self-explanatory names carry meaning.

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: 'Surface area of rect prism.' An agent can tell this computes surface area rather than volume (unlike sibling x402-rect-prism-volume), though the phrasing is terse and does not explicitly mention the verb 'calculate.'

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 explicit when-to-use guidance or named alternatives; the implicit usage (compute surface area from dimensions) is clear from the resource name. The second sentence covers payment/trial terms, not tool selection.

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