Reserved documentation domains are a small, permanently set-aside set of domain names that exist for one purpose: to be used as placeholders. They are defined so that specifications, manuals, tutorials, and sample code can show a realistic-looking name without ever colliding with a real, registrable domain. Because they can never be bought or delegated to real name servers, nothing you write today can accidentally send traffic, email, or credentials to somebody else tomorrow.
Four top-level domains are held back from public registration. They cover the common placeholder cases: illustrative examples, private testing, guaranteed-invalid names, and the local machine. The status pill tells you how strongly each one is reserved.
| Name | Purpose | Status | Governing clause |
|---|---|---|---|
| .example | Illustrative examples in documents, tutorials, and sample code. | Reserved | Set aside for examples by RFC 2606 Section 2, and reinforced as special-use by RFC 6761. |
| .test | Private testing and documentation of software that must never resolve on the public internet. | Special-use | Reserved for testing by RFC 2606 Section 2, with resolution rules in RFC 6761 Section 6.2. |
| .invalid | Guaranteed-invalid names for error paths, placeholders, and obviously fake addresses. | Special-use | Declared permanently invalid by RFC 2606 Section 2, with resolution rules in RFC 6761 Section 6.4. |
| .localhost | The local machine itself, for loopback services and offline development. | Special-use | Names under this TLD must resolve to loopback, as specified in RFC 6761 Section 6.3 and previously reserved by RFC 2606. |
Three second-level domains sit inside the real .com, .net, and .org registries but are permanently withheld from registration. They are the safest possible choice when you want a name that looks exactly like a production website.
| Name | Purpose | Status | Governing clause |
|---|---|---|---|
| example.com | The canonical placeholder website for documentation, screenshots, and sample data. | Reserved | Reserved for examples by RFC 2606 Section 3. |
| example.net | A second placeholder host, useful when a document needs two distinct example sites. | Reserved | Reserved for examples by RFC 2606 Section 3. |
| example.org | A third placeholder host, often used for non-commercial or organizational examples. | Reserved | Reserved for examples by RFC 2606 Section 3. |
The rule of thumb is simple: these names are safe precisely because nothing can ever live on them. The guardrails below keep it that way.
Each snippet below uses example.com as the placeholder host. Copy it as-is into documentation or test code; the name is reserved for exactly this use by RFC 2606.
HTML
<!-- Documentation link: safe to copy into any spec -->
<a href="https://example.com/docs/getting-started">
Getting started
</a>
<img src="https://example.com/logo.png" alt="Example site logo">JavaScript
const apiBase = "https://example.com/api/v1";
async function loadUsers() {
const res = await fetch(`${apiBase}/users`);
return res.json();
}Python
import urllib.request
url = "https://example.com/api/v1/users"
with urllib.request.urlopen(url) as response:
print(response.status, response.read().decode())cURL
curl -i https://example.com/api/v1/usersThe reserved name example.com answers with a minimal, stable page. Here is the kind of 200 OK response you can quote in documentation, exactly as the name is reserved for illustrative use by RFC 2606.
HTTP/1.1 200 OK
Content-Type: text/html; charset=UTF-8
Content-Length: 1256
Connection: close
<!doctype html>
<html lang="en">
<head>
<title>Example Domain</title>
</head>
<body>
<h1>Example Domain</h1>
<p>This domain is for use in illustrative examples in documents.</p>
</body>
</html>Documentation domains — never for production use. Every name on this page exists for examples, tests, and mock-ups only. Do not point real users, real mail, or real configuration at them.
This document defines the reserved names themselves: the .test, .example, .invalid, and .localhost top-level domains plus the reserved second-level names example.com, example.net, and example.org.
This document explains how resolvers and other software must treat those names so that they never leak into the public DNS.