Welcome to Fawlty Language!

Fawlty Language is an IDL8 (Interactive Data Language) compatible compiler (IDL is a registered trademark of NV5 Geospatial Solutions, Inc.



FL is freeware, you can use it without any restriction, you can even redistribute it if you want.

Update for Windows users

Qt 6 changed HiDPI scaling on Windows and FL is not handling this properly, resulting in TVRD() crashing with FullHD+ displays. If you encounter this bug, set the QT_ENABLE_HIGHDPI_SCALING environment variable to 0 before starting FL. (Modifying the global environment is not recommended, as other Qt applications may need HiDPI scaling, it is better to create a batch file to start FL with this setting.)


FL 0.79.54 current development snapshot (21/Jan/2024)

Experimental builds:

FL 0.79.53 previous development snapshot (10/Apr/2023)

Note for Linux users:

Qt6 requires a lot of X11 libraries. The ldd /path/to/fl/fl_0.79.50/bin/platforms/libqxcb.so command shows which libraries are needed. The required X11 runtime packages differ from distribution to distribution, eg. for aarch64 ubuntu 18.04.5 the following system packages are used:

Check whether you have all these packages installed.


Just unpack the archive. The command-line and graphical interfaces are separated into two executables on all platforms. The CMD executable can be started from a terminal/console, while the GUI executable can be started by (double)clicking on it in a file manager.


FL is almost 100% compatible with IDL 8.0. IDL documentation is available on the net at Harris Geospatial Solutions.

IDL programs

Small IDL programs I find useful: pro


Questions, comments, bug reports can be sent to: FawltyLanguage a_t gmail d_o_t com or you can report bugs in the BitBucket issue tracker.


Lajos Földy

Last modified: 2024/January/21.