Libidn README – Introduction information

Libidn is a package for internationalized string handling based on the Stringprep, Punycode, IDNA2003 and TLD specifications. Libidn is a GNU project. For technical reference, see:

WARNING! The IDNA2003 specifications have been superseded by IDNA2008 which is implemented by Libidn2 https://www.gnu.org/software/libidn/#libidn2. The only reasonable use of the libidn library today is to support the historic IDNA2003 behaviour or to use Stringprep profiles. Please try to migrate to libidn2 wherever possible.

If this file came to you as part of a tar archive, then see the file (INSTALL)[INSTALL] for generic compilation and installation instructions. Before building you should consider installing the dependencies. If you obtained this file as part of a “git clone”, then see the CONTRIBUTING.md file.

If you need help to use Libidn, or wish to help others, you are invited to join our mailing list help-libidn@gnu.org, see https://lists.gnu.org/mailman/listinfo/help-libidn.

For more information, see https://www.gnu.org/software/libidn/.

Documentation

GNU Libidn Manual

Libidn API Reference Manual

License

The source code for the C library (libidn.a or libidn.so), the C# library (Libidn.dll) and the Java library (libidn-*.jar) are dual-licensed under the terms of either the GNU General Public License version 2.0 or later - see the file COPYINGv2 - or the GNU Lesser General Public License version 3.0 or later - see the file COPYING.LESSERv3 - or both in parallel as here.

The author of the Java library has agreed to also distribute it under the Apache License Version 2.0, see the file java/LICENSE-2.0.

The manual is licensed under the GNU Free Documentation License, Version 1.3 or any later, see the file doc/fdl-1.3.texi.

The command line tool, self tests, examples, and other auxiliary files, are licensed under the GNU General Public License version 3.0 or later, see the file COPYING.

The library embed data tables published by Unicode, Inc and The Internet Society (IETF), see doc/specification/.

Other files are licensed as indicated in each file. There may be exceptions to these general rules, see each file for precise information.

For any copyright year range specified as YYYY-ZZZZ in this package note that the range specifies every single year in that closed interval.

Copyright (C) 2002-2025 Simon Josefsson Copying and distribution of this file, with or without modification, are permitted in any medium without royalty provided the copyright notice and this notice are preserved.