Critcl lets you easily embed C code in Tcl. Online documentation at
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Compiled Runtime In Tcl

  • Welcome to the C Runtime In Tcl, CriTcl for short, a system to build C extension packages for Tcl on the fly, from C code embedded within Tcl scripts, for all who wish to make their code go faster.


  • The main website of this project is

    It provides access to pre-made binaries and archives for various platforms, and the full documentation, especially the guides to building and using Critcl.

    Because of the latter this document contains only the most basic instructions on getting, building, and using Critcl.


  • Version 3 is the actively developed version of Critcl, with several new features, listed in section New Features, below. This version has changes to the public API which make it incompatible with packages using Critcl version 2.x, or earlier.

  • The last of version 2 is 2.1, available at the same-named tag in the repository. This version is not developed anymore.

Getting, Building, and Using Critcl

  • Retrieve the sources:

    % git clone

    Your working directory now contains a directory critcl.

  • Build and install it:

    Install requisites: cmdline, md5; possibly one of tcllibc, Trf, md5c to accelerate md5.

    % cd critcl

    % tclsh ./build.tcl install

    The generated packages are placed into the [info library] directory of the tclsh used to run build.tcl. The critcl application script is put into the directory of the tclsh itself (and modified to use this executable). This may require administrative (root) permissions, depending on the system setup.

  • It is expected that a working C compiler is available. Installation and setup of such a compiler is platform and vendor specific, and instructions for doing so are very much outside of scope for this document. Please find and read the documentation, how-tos, etc. for your platform or vendor.

  • With critcl installed try out one of the examples:

    % cd examples/stack

    % critcl -keep -cache B -pkg cstack.tcl

    % critcl -keep -cache B -pkg stackc.tcl

    % tclsh

    > lappend auto_path [pwd]/lib

    > package require stackc

    > stackc create S

    > S push FOO

    > S size

    > S destroy

    > exit


New Features

  • Declaration, export and import of C-APIs through stubs tables.

  • Generation of source packages from critcl-based code containing a TEA-based buildsystem wrapped around the raw critcl.

  • Declaration, initializaton and use of user-specified configuration options. An important use is the declaration and use of custom build configurations, like 'link a 3rd party library dynamically, statically, build it from copy of its sources, etc.', etc.

  • This is of course not everything. For the details please read the Changes sections of the documentation.


  • Too much to cover here. Please go to for online reading, or the directories embedded/www and embedded/man for local copies of the documentation in HTML and nroff formats, respectively.


  • 2013-01-21 : Move code to from jcw to andreas-kupries.

  • 2011-08-18 : Move code to public repository on GitHub

    The Subversion repository at svn:// is now obsolete.
    GitHub has the new official repository for Critcl.