# ipv6tool.com — IPv6 Connectivity Test & API

ipv6tool.com is a free, no-auth IPv6 connectivity test tool for humans and a
JSON/Markdown API for AI agents and developers. It detects IPv4 and IPv6
addresses, reports which protocol the browser prefers, and classifies arbitrary
IP addresses by type (global-unicast, link-local, ULA, multicast, loopback, etc.).
No ads, no sign-up, no rate limits.

## CRITICAL CAVEAT FOR AI AGENTS

The API endpoints report the IP address of the **caller** — the machine making
the HTTP request. They **cannot** test a third party's network connectivity.
To test a human user's IPv6 connectivity, use /api/testlink to get a URL and
ask the user to open it in their own browser.

## API Endpoints (all return JSON; add ?format=md or Accept: text/markdown for Markdown)

- GET https://ipv6tool.com/api/check
  Returns the caller's IP, version (4 or 6), and is_ipv6 flag.
  curl https://ipv6tool.com/api/check

- GET https://ipv6tool.com/api/v4
  Returns the caller's IPv4 address, or null if connecting over IPv6.
  curl https://ipv6tool.com/api/v4

- GET https://ipv6tool.com/api/v6
  Returns the caller's IPv6 address and has_ipv6 boolean.
  curl https://ipv6tool.com/api/v6

- GET https://ipv6tool.com/api/lookup?ip=<addr>
  Validate and classify any IPv4 or IPv6 address. Returns: valid, version,
  is_ipv6, type, compressed, expanded. No external calls — pure validation.
  curl "https://ipv6tool.com/api/lookup?ip=2001:db8::1"

- GET https://ipv6tool.com/api/testlink
  Returns {"url":"https://ipv6tool.com/"} — share this with a human user so
  their browser runs the real connectivity test. Use this when an agent is
  asked to test someone else's IPv6 connectivity.
  curl https://ipv6tool.com/api/testlink

## curl examples

# Get my own IP and version (JSON):
curl https://ipv6tool.com/api/check

# Get my own IP and version (Markdown, AI-paste-ready):
curl "https://ipv6tool.com/api/check?format=md"

# Classify an IPv6 address:
curl "https://ipv6tool.com/api/lookup?ip=fe80::1"

## MCP Server

An MCP server is planned. Check https://ipv6tool.com/ for updates.

## Human-facing tool

https://ipv6tool.com/ — dark minimal UI, auto-detects IPv4 + IPv6, shows verdict.