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

The annotations say readOnlyHint=false and destructiveHint=false, and the description usefully explains why: this is a metered call that debits prepaid credits from the supplied key. That is real value beyond the annotations. It stops short of stating cost per call, what happens on insufficient balance, or whether errors still consume credits.

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, zero filler, with the returned resource front-loaded ahead of the billing note. It is not padded, though the second sentence reads like a separate billing concern rather than integrated guidance.

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 only two parameters and no output schema, the description should say what comes back (a list of domain strings? objects with metadata?). It does not, and it gives no failure semantics for a credit-metered call, so an agent must probe to learn the response shape.

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 50%: 'creditKey' is already documented in the schema as the reusable key from x402-credit-purchase, and the description only reinforces that. The 'company' parameter gets just the phrase 'company name', adding little about format, matching behavior, or whether legal suffixes matter.

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 first sentence names the resource (domains) and its input (a company name) in a compact lookup framing, so an agent knows what it retrieves. However, it never distinguishes this from the near-identically named sibling 'company-to-url', leaving the agent to guess whether they differ in cost, output, or coverage.

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 choose this paid variant over the free-sounding 'company-to-url' or over 'x402-domain-lookup'. The mention of credit deduction implies a paid path, but the agent gets no explicit decision rule or precondition.

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