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.

Some structurally well-formed databases under test-data/ are deliberately hostile and can exhaust an unprotected reader. Do not fully decode every fixture without resource controls. See the denial-of-service test data documentation.

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.