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

No annotations are supplied, so the description carries the full behavioral burden. It does disclose one genuinely useful trait - a pay-per-call service with a 5-call free trial tied to a signed wallet - but says nothing about computational behavior, output shape, limits on n/count, or what happens after the trial is exhausted.

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-loaded, but the first sentence is pure redundancy with the name and title, leaving only the emoji-prefixed pricing line as new information. It is brief without being informative.

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?

With no annotations, no output schema, four undocumented parameters and multiple indistinguishable Fibonacci siblings, the definition omits nearly everything an agent needs to invoke it correctly. Only the pricing constraint is covered.

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?

Four parameters (n, count, index, sequence) have 0% schema description coverage and the description adds no meaning whatsoever. The overlap between n, count and index is genuinely ambiguous, and 'sequence' is entirely unexplained, so an agent cannot know which field to populate.

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 text 'Fibonacci: Fibonacci numbers' restates the tool name rather than describing an operation - there is no verb saying whether it returns the nth term, a count of terms, or a sequence. It also fails to distinguish this from sibling tools like x402-fibonacci-n, x402-fibonacci-index, x402-fibonacci-series and x402-is-fibonacci, which is critical given how many near-identical Fibonacci tools exist.

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 guidance on when to choose this tool over the four sibling Fibonacci tools, no stated input requirements, and no scope limits. The only additional sentence concerns billing ('5 free trial calls per signed wallet'), which is not usage guidance.

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