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

Annotations declare readOnlyHint=false, destructiveHint=false and openWorldHint=false, so the safety profile is mostly covered. The description adds genuinely useful context by disclosing that the call deducts prepaid credits from a reusable key, which the annotations do not express. It stops short of stating cost per call, what happens when credits run out, or error 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 short sentences with no filler; the operation is stated first, followed by the billing side effect. Only mild deduction for the vague 'Raw Domain API JSON' phrasing, which uses words without adding meaning.

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 two-parameter, credit-consuming tool with no output schema, the description covers purpose, input format and billing, which is the minimum. Missing are the return shape indication, per-call credit cost, and failure modes on invalid keys or insufficient balance, all of which matter for a metered tool.

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 only 50%: creditKey is documented in the schema, but lookup has no schema description. The description partially compensates by explaining that lookup accepts one or more comma-separated domains, which is the format detail an agent most needs. It adds nothing about creditKey beyond what the schema already says.

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 gives a verb ('lookup') and resource ('Domain API JSON') plus scope ('one or more comma-separated domains'), so the basic operation is inferable. However, 'Raw Domain API JSON' is jargon that doesn't clarify what data actually comes back, and nothing distinguishes it from the similarly named siblings such as domain-api-json or x402-domain-api.

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 explicit when-to-use guidance and no named alternative. Given the catalog contains near-identical names (domain-api-json, domain-api, x402-domain-api, domain-lookup), the absence of any routing hint leaves the agent guessing which one to call.

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