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

With no annotations, the description carries the full burden, and it does disclose the pricing model ("5 free trial calls per signed wallet"), which is real behavioral context an agent needs. It omits what the response looks like and says nothing about acceptable numeric formats, so the disclosure is partial rather than complete.

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?

Three short sentences, front-loaded with the definition before the input instruction and the trial-call note. The emoji and promotional framing of the last clause is mildly wasteful but not disruptive.

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 two-input calculator with no output schema, the description should at minimum establish units and the shape of the returned value; it establishes neither. The free-trial detail is a nice addition, but an agent still cannot tell whether mass is in kg or velocity in m/s.

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 typed only as unconstrained strings. The description repeats the parameter names but adds no unit convention, no accepted format (numeric string, decimals, negatives), and no indication whether either is required despite both being optional in the schema.

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?

States a specific verb and resource ("Calculate momentum in physics") and spells out the formula ("mass multiplied by velocity"), which lets an agent distinguish it from neighbors like x402-velocity, x402-impulse, or x402-kinetic-energy. It stops short of naming an alternative, but the physics definition is unambiguous.

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 only guidance is "Provide mass and velocity values," which restates the parameter names rather than saying when to pick this over sibling calculators or what the inputs must look like. No exclusions, prerequisites, or alternative tools are mentioned.

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