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

No annotations are supplied, so the description carries the full disclosure burden. The free-trial note does add genuine context about authentication (a signed wallet) and a quota (5 calls), which is real behavioral information. However, the critical behaviors are undisclosed: whether the input is a decimal fraction (0.5 -> 50%) or an already-scaled percent (50 -> 50%), how negatives or rounding are handled, and what the returned string looks like.

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?

It is short and front-loaded with the core action, which is good. But roughly half the text is a promotional emoji line, and the space saved by brevity is spent on marketing rather than on the input/output semantics that are actually missing.

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 two-parameter formatter with no annotations, no output schema, and zero parameter documentation, the description leaves too much unspecified. An agent cannot determine the expected input scale, the meaning of `decimals`, or the output shape without trial and error.

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 there are two parameters, so the description must compensate and does not. "A number" gives a faint hint that `value` is numeric input, but the `decimals` parameter, which controls output precision, is never explained; an agent must guess whether it takes a count, a string, or a format token.

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?

It states a verb and a resource ("format a number as a percentage"), which does convey direction of transformation, but the phrase is essentially a restatement of the tool name "x402-format-percent". It gives an agent no basis for distinguishing this from close siblings such as x402-percent, x402-format-decimal, x402-format-fixed, or x402-percent-to-ratio.

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 guidance and no named alternative, despite a dense field of near-duplicate siblings (x402-percentage-of, x402-percent-to-ratio, x402-format-significant). The only extra sentence concerns free trial credits, which is pricing information, not selection guidance.

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