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

With no annotations, the description must carry the behavioral burden, and it does disclose the core calculation and required inputs. However, it does not describe the output format, expected units, edge-case handling, or behavior when values are missing or invalid.

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 short and front-loads the formula, which is appropriate for a simple calculator tool. The leading 'Momentum:' label is redundant with the tool name but does not seriously harm clarity.

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 low-complexity physics calculator, the formula and requested inputs are mostly sufficient, but there are gaps: no output format, no units, and no indication of what the tool expects given that the schema has zero parameters. The mismatch between 'Provide mass and velocity values' and an empty input schema is a notable completeness issue.

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 is empty, so the description adds value by naming the two needed values: mass and velocity. It does not specify units, types, or formats, but given the schema provides no parameter information at all, the description is the only useful source of input semantics.

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 clearly identifies the operation ('Calculate momentum in physics') and states the formula (mass multiplied by velocity), so an agent understands what the tool does. It does not explicitly distinguish itself from physics-related siblings like x402-velocity or x402-force, though the formula provides some implicit differentiation.

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 guidance is given for when to use this tool versus alternatives such as x402-velocity or x402-acceleration. The instruction to 'Provide mass and velocity values' implies the required inputs but does not state prerequisites, exclusions, or alternative tools.

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