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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It fails to say what operation is performed, what input it consumes, what it returns, or any constraints. 'Diagonal of rectangular' conveys no behavioral trait beyond the tool name itself.

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?

The single sentence is under-specified rather than concise: it contains a grammar error ('of rectangular' instead of 'of a rectangle') and every word is redundant with the tool name. There is no content to be well-structured.

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 annotations, no output schema, an empty input schema, and a one-line tautological description, an agent cannot call this tool correctly. Inputs, output shape, and the distinction from x402-cuboid-diagonal or x402-matrix-diagonal are all missing — completely inadequate for a geometric computation tool.

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?

The schema is empty, yet computing a rectangle's diagonal inherently requires dimensions — the description never explains how inputs are supplied or why none are needed. Even with the 0-parameter baseline, the description adds zero meaning and leaves the fundamental input question unresolved, so it earns no credit above a minimal score.

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 'Rectangular Diagonal: Diagonal of rectangular' merely restates the tool name in a grammatically broken phrase. It does not state what the tool computes, what a rectangle diagonal is, or how it differs from siblings like x402-cuboid-diagonal, x402-cube-diagonal, and x402-matrix-diagonal. This is a textbook tautology.

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 guidance on when to use this tool versus its many geometry siblings. With hundreds of x402-* alternatives including x402-cuboid-diagonal, x402-cube-diagonal, x402-matrix-diagonal, and x402-parallelogram-area, an agent has no basis to select this tool over any related one.

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