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

With no annotations provided, the description carries the full burden of behavioral disclosure. It only states the operation ('format a number with significant figures') without revealing how many significant figures are applied, what rounding rules are used, whether the tool accepts arbitrary input, or what the return value looks like. The empty input schema is also not addressed, so an agent cannot infer how a number is supplied.

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 a single sentence, which is concise, but it is under-specified rather than efficiently structured. It contains a redundant label ('Format Significant') followed by a definition that mostly restates the tool name. There is no additional context or structure that helps an agent use the tool.

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 has no annotations, no output schema, and an empty input schema, the description is the only source of information. It is far from complete: it does not explain how to invoke the tool, how the number is supplied, what significant figures means in terms of output, or how it differs from similar siblings. An agent cannot correctly call this tool based on the provided definition.

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?

The input schema has zero properties, so the baseline is 4 for parameter semantics, but the description claims to format 'a number' without explaining how that number is passed. This is a critical gap: the description implies input but provides no parameter names, types, or formats, leaving an agent unable to construct a valid call. The description does not compensate for the empty schema.

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 clearly states a specific action: 'Format a number with significant figures.' This is a concrete verb+resource pair that tells an agent what the tool does. However, it does not distinguish this tool from closely related siblings like x402-sig-figs, x402-significant-digits, or x402-format-scientific, so it falls short of full sibling differentiation.

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 description provides no guidance on when to use this tool versus alternatives. Given the huge sibling list includes x402-sig-figs, x402-significant-digits, x402-round-to, and x402-format-scientific, an agent has no basis for selecting this one. There is no mention of input expectations, context, or exclusions.

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