check_domain

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

No annotations are provided, so the description carries the full burden. It discloses the cost ($0.001 per call), the payment method (USDC over x402 to x402-domains), and the return payload (merchant's artifact and payment receipt). This is a strong disclosure for a paid tool, though it stops short of covering edge cases or failure 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?

Two sentences, front-loaded with the primary purpose, followed by cost and return information. Every sentence earns its place; there is no fluff or repetition of schema details.

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 relatively simple paid lookup tool, the description covers the essential context: what it does, what it costs, how to pay, and what is returned. Since there is no output schema, the description appropriately substitutes by naming the return items. This is complete for practical use.

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 coverage is 100% for both parameters: 'domain' is described with an example, and 'rail' has a clear enum with default behavior. The description adds no additional parameter semantics beyond the schema, so the baseline 3 is appropriate.

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?

Purpose is clearly stated with a specific verb ('Check') and resource ('domain'), and it distinguishes itself from sibling tools by describing the exact output: registration status, holder, and expiry. This is unambiguous and unlikely to be confused with any other tool.

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 clearly implies when to use the tool: when you need domain registration details. It doesn't explicitly mention alternatives or exclusions, but the context is clear enough given the unrelated sibling tools, so no further guidance is strictly needed.

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