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 actual algorithm and the pricing model ('5 free trial calls per signed wallet'), which is real value beyond structured fields. However, it never states the return type (presumably boolean), nor how non-numeric or out-of-range input is handled.

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 front-loaded sentence with the purpose first, the method second, and a payment note last. The emoji pricing tag is mild noise but the whole thing is short and readable.

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 one-parameter predicate with no output schema, the definition explains what is computed but omits the return shape and edge-case behavior. Adequate but not complete for an agent that needs to know what it will get back.

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 coverage is 0% and the single 'value' parameter has no type description, so the description must compensate. The formula '5*value^2' does clarify that value is the number being tested, but it leaves the string-vs-number ambiguity and input constraints unaddressed.

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 predicate: it tests whether a value is a Fibonacci number, and even names the mathematical criterion (5*value^2 ± 4 is a perfect square). This distinguishes it in spirit from sibling generators like x402-fibonacci-n or x402-fibonacci-series, though it never names them.

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 when-to-use or when-not-to-use guidance, and no routing to alternatives such as x402-fibonacci-n (nth term) or x402-fibonacci-index. The agent must infer from the tool name alone which of the many Fibonacci siblings to pick.

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