RDAP API

Domain Lookup

domain-lookup

Read-only

Look up normalized RDAP registration data (registrar, status, dates, nameservers, contacts) for a domain name.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "domain": "<domain>"
    },
    "name": "domain-lookup"
  }
}

Input Schema

Name	Required	Description
`whois`	No	Set false to refuse the WHOIS fallback, so a TLD with no RDAP server errors instead of answering over port 43. Defaults to true.
`domain`	Yes	The domain name to look up, e.g. "example.com". Unicode (IDN) names are accepted. Pass the registered domain, not a host such as "www.example.com".
`follow`	No	Follow the registrar RDAP link for richer data on thin registries such as .com and .net. Slower; defaults to false.

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedOct 16, 2026

changedInput schema / properties / domain / description

Previous value: -"The domain name to look up, e.g. \"example.com\". Unicode (IDN) names are accepted."New value: +"The domain name to look up, e.g. \"example.com\". Unicode (IDN) names are accepted. Pass the registered domain, not a host such as \"www.example.com\"."

First observedSep 6, 2026

TDQS

A3.6/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=true, openWorldHint=true and destructiveHint=false, so the safety profile is covered. The description usefully adds the shape of the returned data, but says nothing about the WHOIS/port-43 fallback or the latency of the follow behavior, both of which are notable traits disclosed only in the parameter descriptions.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

A single front-loaded sentence naming the operation, the data type, the key input, and the returned fields, with no filler.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

With no output schema, the description compensates by enumerating the principal return fields, and the schema covers the two behavioral flags. It lacks any routing guidance among the sibling lookup tools, which is the only material gap.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100%, so the schema already explains domain, whois and follow semantics in detail. The description adds no parameter-level meaning beyond that, which is the correct baseline when the schema does the heavy lifting.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description gives a specific verb ("Look up") and resource (normalized RDAP registration data for a domain name) and enumerates the returned fields (registrar, status, dates, nameservers, contacts). It is clear what the tool does, though it never names or distinguishes itself from the close sibling bulk-domain-lookup.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines3/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Usage is only implied: the singular "for a domain name" suggests one-domain lookups versus bulk-domain-lookup, and the schema warns to pass a registered domain rather than a host. There is no explicit when-to-use, when-not-to-use, or pointer to entity-lookup/asn-lookup alternatives.

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

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