.NET Reader for the MaxMind DB Database Format
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MaxMind DB Reader


This is the .NET API for reading MaxMind DB files. MaxMind DB is a binary file format that stores data indexed by IP address subnets (IPv4 or IPv6).


This library works with .NET Framework version 4.5 and above and .NET Standard 1.4 or above.



We recommend installing this library with NuGet. To do this, type the following into the Visual Studio Package Manager Console:

install-package MaxMind.Db


Note: For accessing MaxMind GeoIP2 databases, we generally recommend using the GeoIP2 .NET API rather than using this package directly.

To use the API, you must first create a Reader object. The constructor for the reader object takes a string with the path to the MaxMind DB file. Optionally you may pass a second parameter with a FileAccessMode enum with the value MemoryMapped or Memory. The default mode is MemoryMapped, which maps the file to virtual memory. This often provides performance comparable to loading the file into real memory with the Memory mode while using significantly less memory.

To look up an IP address, pass a string representing the IP address to the Find<T> method on Reader. This method will return the result as type T. T may either be a generic collection or a class using the [MaxMind.Db.Constructor] attribute to declare which constructor to use during deserialization and the [MaxMind.Db.Parameter("name")] to map the database key name to a particular constructor parameter.

We recommend reusing the Reader object rather than creating a new one for each lookup. The creation of this object is relatively expensive as it must read in metadata for the file.


using (var reader = new Reader("GeoIP2-City.mmdb"))
    var data = reader.Find<Dictionary<string, object>>("");

Multi-Threaded Use

This API fully supports use in multi-threaded applications. In such applications, we suggest creating one Reader object and sharing that among threads.


The MaxMind DB format is an open format for quickly mapping IP addresses to records. See [the specification] (https://github.com/maxmind/MaxMind-DB/blob/master/MaxMind-DB-spec.md) for more information on the format.

Bug Tracker

Please report all issues with this code using the [GitHub issue tracker] (https://github.com/maxmind/MaxMind-DB-Reader-dotnet/issues).

If you are having an issue with a MaxMind database or service that is not specific to this reader, please [contact MaxMind support] (http://www.maxmind.com/en/support).


Patches and pull requests are encouraged. Please include unit tests whenever possible.


The MaxMind DB Reader API uses Semantic Versioning.

Copyright and License

This software is Copyright (c) 2016 by MaxMind, Inc.

This is free software, licensed under the Apache License, Version 2.0.