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

No annotations exist, so the description carries the full burden. It does disclose a real behavioral trait beyond the schema — the output level list and the pricing/access model ('5 free trial calls per signed wallet') — but says nothing about input validation (e.g., high < low), numeric format, or error behavior.

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 states the purpose, inputs, and outputs with no wasted prose. The trailing emoji/promo fragment about free trial calls is minor boilerplate that slightly dilutes an otherwise tight description.

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, listing the returned retracement levels usefully compensates for the missing return documentation. However, with no annotations and 0% schema coverage, the absence of any input format or validation guidance leaves a meaningful gap.

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 the two parameters (low, high) are only restated by name in the description. It adds the vague context that they are price levels, but no format, units, ordering rule, or required-ness, leaving the schema's documentation gap largely unfilled.

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 gives a specific verb and resource ('Computes Fibonacci retracement price levels') and states the exact output set (0, 0.236 ... 1), which clearly separates it from sibling sequence tools like x402-fibonacci-series or x402-is-fibonacci. It does not name a sibling explicitly, so it falls just short of the 5 bar.

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 phrase 'from a high and low' implies the inputs a caller must have (two price extremes) and therefore when the tool applies, but there is no explicit when-to-use, when-not-to-use, or alternative tool named. Usage is only implied.

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