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

With no annotations, the description carries the full load and does well: it discloses durable state creation ("stores a snapshot"), the returned delta fields, repeat-check intent, and the paid x402 model with price and chain. It omits failure behavior (e.g. what check does with no prior snapshot) and what create returns.

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?

Front-loaded with the core purpose, then the action semantics, then cost/payment, then endpoint. Dense with no filler sentences; the raw HTTP URL is marginally useful but doesn't crowd out the essentials.

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?

No output schema exists, and the description compensates by listing the diff fields returned (status, registrar, expiry, nameservers, countdown). Also surfaces cost and payment mechanics that no structured field covers. Gaps are error/empty-snapshot behavior and the create 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 100% so baseline is 3, but the description adds material schema-external detail: payment is supplied via params._meta["x402/payment"], which is not represented in the input schema at all. Domain and action semantics are already in the schema and only restated.

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 and resource ("Watch a domain's RDAP registration facts") and immediately clarifies the two-mode behavior: create stores a snapshot, check returns the delta. An agent can tell this apart from domfacts__rdap and domfacts__dns because the snapshot/diff model is explicit.

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?

"Built for repeat checks" plus the create-then-check sequencing gives clear usage context, and the action enum restates it. It stops short of naming an alternative tool (e.g. domfacts__rdap) for a one-off lookup, so the when-not-to-use case is left to inference.

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