MaxMind DB is a binary file format that stores data indexed by IP address subnets (IPv4 or IPv6).

This repository contains the spec for that format as well as test databases.

Generating Test Data

The write-test-data command generates the MMDB test files under test-data/ and bad-data/.

When run from anywhere inside this repository, it auto-detects the repo root and uses default paths:

go run ./cmd/write-test-data

You can override any path with flags:

go run ./cmd/write-test-data \
  -source ./source-data \
  -target /tmp/test-out \
  -bad-data /tmp/bad-out

Copyright and License

This software is Copyright (c) 2013 - 2026 by MaxMind, Inc.

This is free software, licensed under the Apache License, Version 2.0 or the MIT License, at your option.