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

With no annotations, the description carries the full burden, but it provides no information about behavior—no mention of return format, input expectations, or what 'Is Fermat' actually evaluates. The description is effectively content-free.

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 extremely short but fails to be informative; it is under-specified rather than concise. It does not front-load any useful information.

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?

Given the tool's likely complexity (a number-theoretic predicate) and the lack of annotations or output schema, the description is completely inadequate. An agent cannot determine what the tool does or when to use it.

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 100%, so the single parameter 'value' is documented as 'Value to process'. The description adds no additional meaning, but the baseline is 3 when the schema does the heavy lifting.

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 'Is Fermat: Is Fermat' is a near-tautology that restates the tool name without stating what the tool actually checks. It does not clarify whether it tests a number for being a Fermat number, a Fermat prime, or something else, and there are sibling tools (x402-is-fermat-prime, x402-is-fermat-prime-num) that make this distinction critical.

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 use this tool versus alternatives. Given the presence of x402-is-fermat-prime and x402-is-fermat-prime-num, the lack of any differentiation is a serious omission.

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