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

With no annotations, the description carries the full burden and does so well: it discloses pricing ($0.012 USDC via x402 per call), partial-failure semantics ("bad items return per-item errors"), and the fields each item returns (registrar, dates, DNS, SPF, DMARC, HTTPS reachability). It omits operational traits like rate limits, retry/idempotency behavior, and what happens on payment failure, keeping it below a 5.

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?

Dense but front-loaded: batch scope and cost advantage come first, then body format, returns, and error behavior. The literal example-output JSON is somewhat long, though it usefully conveys the response envelope in the absence of an output schema.

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 paid batch endpoint with no annotations and no output schema, the description covers cost, request shape, return fields, error handling, and an example response shape. What is left out — rate limits and payment failure modes — is minor but non-zero for a monetized 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 100% and the single `domains` array is already documented as "1 to 10 domain names". The description restates the JSON body shape `{domains:[...]}` and the max of 10, adding no syntax or format detail the schema lacks. A 3 baseline is correct when the schema does the work.

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?

States a specific verb/resource combination (batch domain intelligence) and the exact scope: up to 10 domains per call. It distinguishes itself from the single-domain sibling by explicitly claiming to be "60% cheaper than singles", so an agent can choose between domain_lookup and domain_lookup_batch without opening either schema.

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?

Gives concrete context ("due diligence and lead lists"), a hard batching limit (10 per call) and an economic reason to prefer it over the singles tool. It stops short of explicitly saying "for a single domain use domain_lookup instead", so the routing is implied rather than stated.

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