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

No annotations are provided, so the description must carry the full behavioral burden. It does not state that this is a pure/read-only calculation, does not describe the expected input type beyond the schema, and does not clarify output format or edge cases.

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 a single, front-loaded sentence with no wasted words. It is appropriately sized for a simple calculation tool, though it omits useful detail rather than being overly verbose.

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 simple, single-parameter math tool with no output schema, the description minimally identifies the operation. However, it does not specify that the result is the face diagonal length or clarify how the input side maps to the calculation, leaving a small but meaningful gap.

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 100% for the single 'side' parameter, so the schema already provides baseline documentation. The description adds no extra meaning about what 'side' refers to (e.g., edge length) or its accepted format, matching the baseline 3 for high schema coverage.

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 states a specific geometric quantity, 'Face diagonal of a cube,' which distinguishes it from the sibling x402-cube-space-diagonal. The verb is implicit ('calculate') rather than explicit, but the resource and scope are clear enough for an agent to identify the tool.

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 gives no guidance on when to use this tool versus alternatives such as x402-cube-space-diagonal or x402-cuboid-diagonal. It merely states what the tool computes, leaving selection entirely to the reader.

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