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

Annotations already establish readOnly, idempotent, non-destructive, open-world behavior, so the bar is lower. The description adds genuinely non-structured context: a free-sample quota per day and a per-call cost of $0.002 USDC via x402, which is exactly the kind of rate-limit/cost disclosure an agent needs. It stops short of describing latency 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, zero waste: purpose first, then cost/quota. Both sentences earn their place and the key information is front-loaded.

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?

An output schema exists, so return values need not be explained, and annotations cover the safety profile. For a low-complexity single-domain check the description is largely sufficient, with the missing when-to-use-vs-siblings guidance being the only notable gap.

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?

With a single parameter at 100% schema coverage, baseline is 3; the schema itself only says 'Domain' with no format hint, and the description adds no syntax guidance such as whether a bare name or FQDN is expected. Schema carries the (thin) load and the description does not compensate.

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 phrase 'Registered or available, straight from the TLD registry' clearly conveys a domain availability/registration-status check against the authoritative registry. The verb is implicit rather than explicit, and it does not name or differentiate itself from siblings like domains__facts or domains__dns, so it falls short of a 5.

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 use this tool versus the many sibling tools (domains__facts, domains__dns, etc.), nor any stated preconditions. The only usage-adjacent content is the pricing/rate-limit note, which is not selection guidance.

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