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

No annotations are supplied, so the description carries the burden. It does add genuine context beyond the name — the free-trial credit model ('5 free trial calls per signed wallet'), which hints at auth/metering — but it omits validation behavior (what happens with non-numeric or invalid side lengths) and never states the operation is a side-effect-free computation.

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?

One short sentence with the resource and inputs front-loaded, plus a one-clause pricing note. No filler, though the emoji trial banner is marginally extraneous to the tool's actual semantics.

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 deterministic math tool with no output schema, the description states what is returned (the perimeter), which is enough to call it. It still leaves gaps on input format and error behavior for invalid side lengths, which the schema does not cover either.

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% with four opaque params (a, b, c, d) typed as strings. The description partially compensates by declaring all four are side lengths, but it does not map which labels are bases vs. legs, nor whether fractional/string numeric input is accepted.

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?

Specific verb+resource: 'Returns the perimeter of a trapezoid' and it names the required inputs (four side lengths). An agent can distinguish it from siblings like x402-trapezoid-area or x402-trapezoidal-rule without opening a schema, though it never explicitly names those alternatives.

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 when-to-use, when-not-to-use, or alternative routing guidance. The only guidance is implicit in the math being performed; an agent must infer that this is for perimeter (not area) problems on its own.

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