To actually run highlight.js it is necessary to build it for the environment where you’re going to run it: a browser, the node.js server, etc.
The build tool is written in Python (for both 2.x and 3.x variants). It also can use YUICompressor for the in-browser builds so make sure you have Java installed for that too.
The tool is located in tools/build.py (tools/build3.py for Python 3). A few useful examples:
python tools/build.py :common
python tools/build.py -t node
python tools/build.py -n python ruby
The full option reference is available with the usual --help option.
The build result will be in the build/ directory.
Testing is done in a browser using the provided src/test.html file that contains snippets for all the supported languages. You can use browser builds with all or only some of the languages, with or without compression.
The usual approach to debugging and testing a language is first building highlight.js with only the language you’re working on without compression (to have readable code in browser error messages). After this you have to build the entire package with all the languages and see if anything is broken. If your language breaks auto-detection it should be fixed by improving relevance and is a black art in and of itself. When in doubt, please refer to the discussion group!