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

With no annotations, the description carries the full burden and does disclose one real behavioral trait: it rejects inputs where x0 equals x1. It also surfaces the payment model (5 free trial calls per signed wallet). It omits, however, output format, numeric-string parsing behavior, and whether non-collinear/out-of-range x values are rejected or extrapolated.

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 core operation is front-loaded in a single efficient sentence. The trailing '🆓 5 free trial calls per signed wallet' is promotional boilerplate that adds a little noise, but the payload remains tight.

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 trivial two-point math helper with no output schema, the description covers purpose and inputs adequately. It stops short of stating the return value shape or numeric precision, and with 0% schema coverage and zero required parameters declared, an agent has no signal about which inputs are actually mandatory.

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%, so the description must compensate, and it does name and assign meaning to all five parameters: x is the query point, x0/y0 and x1/y1 are the two anchor points, and y is the interpolated result. It does not explain why values are typed as strings rather than numbers, which is the one remaining ambiguity.

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+resource ('Linearly interpolates y at a given x from two points x0,y0 and x1,y1'), which is unambiguous on its own. It does not, however, differentiate itself from near-identical siblings like x402-interpolate, x402-lerp, x402-lerp-value, or x402-extrapolation, leaving the agent to guess which is canonical.

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 explicit when-to-use or when-not-to-use guidance and no named alternative. The only conditional statement ('rejecting equal x0 and x1') is an error condition, not a selection rule. Usage is inferable from the operation name but never stated.

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