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 it discloses almost nothing: not whether width/length are parsed as numbers from strings, whether units are assumed, what happens with non-numeric or negative input, or what the return value looks like. The one genuine behavioral disclosure is the pricing model (5 free trial calls per signed wallet), which is useful but unrelated to how the computation behaves.

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?

Two short sentences with the operation front-loaded and no rambling. The second sentence is a promotional/billing line rather than tool-relevant content, but nothing is buried or repetitive.

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?

A simple two-parameter math tool should be trivially completable in one sentence, yet the definition omits the formula, expected input format (strings holding numbers), and output shape, while there are no annotations or output schema to fill those gaps. An agent would have to guess at units and input validity.

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% and both parameters are bare strings named 'width' and 'length'. The description adds no semantics beyond the names — no unit expectations, no numeric format, no indication whether these are the two legs or something else. For a low-coverage schema the description should compensate, and it 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?

The description names the resource (rectangle diagonal) but restates the title rather than stating a verb and computation, e.g. 'compute the diagonal length from width and length using sqrt(w^2+l^2)'. An agent can infer the intent, and the sibling list contains confusable neighbours (x402-cuboid-diagonal, x402-cube-diagonal, x402-cube-space-diagonal, x402-rect-prism-surface) that the description never distinguishes itself from.

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 or when-not-to-use guidance and no mention of which sibling to prefer for 3D or prism cases. The only extra sentence concerns free trial calls per signed wallet, which is billing information, not usage guidance.

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