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, and it discloses nothing at all. It does not state that this is a pure computation, what the result represents, how inputs are supplied, or any error/edge-case behavior. This is strictly weaker than the update_drive calibration example, which had at least a minimal meaningful sentence and scored 2.

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 description is seven words, nearly all duplication, which is under-specification rather than genuine conciseness. It matches the calibration example for 'Process', which scored 2 for the same reason. Nothing is front-loaded because nothing is actually said.

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 cross-product tool with an empty parameter schema and a tautological description gives an agent zero actionable invocation information. The agent cannot know what inputs to provide (the schema declares none), what output format to expect (no output schema), or how this differs from x402-vector-cross. For a tool whose semantics are ambiguous even to a human, this definition is completely inadequate.

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 input schema has 0 parameters with 100% coverage, so per the rubric the baseline is 4 and no parameter documentation is required. The description adds nothing about parameters, but there is nothing for it to add at the individual-parameter level. The deeper question of how two vectors could be passed to a parameterless tool is a contextual completeness issue rather than a parameter-semantics one.

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 'Cross Product2d: Cross Product2d' is a pure tautology; it restates the tool name without adding a verb, resource, or any semantic content. It also fails to clarify whether '2d cross product' means the scalar z-component of a 3D cross product or the 2D perp-dot product, and it does nothing to distinguish this tool from the sibling x402-vector-cross.

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?

The description contains zero guidance on when to use this tool versus alternatives. The extensive sibling list includes closely related tools like x402-vector-cross, x402-vector-dot, and x402-distance2d, none of which are mentioned, so an agent cannot route correctly. It is not actively misleading, so it lands at 'no guidance' rather than 'misleading'.

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