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

No annotations are provided, so the description carries the full burden of behavioral disclosure. It discloses nothing: no side effects, no return behavior, no input expectations, no constraints. The description is completely silent on how the tool behaves.

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?

This is under-specification, not conciseness. The description is short but contains zero information — it earns no credit for brevity because it is merely a restatement of the name with no meaningful content.

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, an empty input schema, and a huge list of contextually similar siblings, the description was the only chance to make this tool usable — and it fails entirely. An agent cannot know what the tool computes, what arguments it accepts, what it returns, or how it differs from x402-sig-figs.

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 schema has 0 parameters, so there is trivially nothing to document and the baseline is 4. However, a significant-digits operation inherently requires a numeric value and precision, and the empty schema plus tautological description leaves the agent unable to determine how input is provided. The description adds no semantic value and fails to clarify the invocation model, justifying a slight deviation below baseline.

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, 'Significant Digits: Significant Digits', is a pure tautology that merely restates the tool name twice. It contains no verb, no stated action, no resource, and no scope — an agent cannot determine what this tool does beyond what the name alone suggests.

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 zero guidance on when to use this tool versus alternatives. Given the sibling list includes x402-sig-figs, x402-format-significant, and x402-round-to — all plausibly overlapping in purpose — the description provides no differentiation or selection criteria whatsoever.

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