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rJSmin - A Javascript Minifier For Python


  1. Introduction
  2. Copyright and License
  3. System Requirements
  4. Installation
  5. Documentation
  6. Bugs
  7. Author Information


rJSmin is a javascript minifier written in python.

The minifier is based on the semantics of jsmin.c by Douglas Crockford.

The module is a re-implementation aiming for speed, so it can be used at runtime (rather than during a preprocessing step). Usually it produces the same results as the original jsmin.c. It differs in the following ways:

  • there is no error detection: unterminated string, regex and comment literals are treated as regular javascript code and minified as such.
  • Control characters inside string and regex literals are left untouched; they are not converted to spaces (nor to \n)
  • Newline characters are not allowed inside string and regex literals, except for line continuations in string literals (ECMA-5).
  • "return /regex/" is recognized correctly.
  • More characters are allowed before regexes.
  • Line terminators after regex literals are handled more sensibly
  • "+ +" and "- -" sequences are not collapsed to '++' or '--'
  • Newlines before ! operators are removed more sensibly
  • (Unnested) template literals are supported (ECMA-6)
  • Comments starting with an exclamation mark (!) can be kept optionally
  • rJSmin does not handle streams, but only complete strings. (However, the module provides a "streamy" interface).

Since most parts of the logic are handled by the regex engine it's way faster than the original python port of jsmin.c by Baruch Even. The speed factor varies between about 6 and 55 depending on input and python version (it gets faster the more compressed the input already is). Compared to the speed-refactored python port by Dave St.Germain the performance gain is less dramatic but still between 3 and 50 (for huge inputs). See the docs/BENCHMARKS file for details.

rjsmin.c is a reimplementation of in C and speeds it up even more.


Copyright 2011 - 2022 André Malo or his licensors, as applicable.

The whole package (except for the files in the bench/ directory) is distributed under the Apache License Version 2.0. You'll find a copy in the root directory of the distribution or online at:


Supported python versions are 2.7 and 3.4+.

You also need a build environment for python C extensions (i.e. a compiler and the python development files).


Using pip

$ pip install rjsmin

Using distutils

Download the package, unpack it, change into the directory

$ python install

The command above will install a new "rjsmin" package into python's library path.


rJSmin effectively consists of two files: and rjsmin.c, the latter being entirely optional. So, for simple integration you can just copy into your project and use it.


The module provides a simple function, called jsmin which takes the script as a string and returns the minified script as a string.

The module additionally provides a "streamy" interface similar to the one jsmin.c provides:

$ python -mrjsmin <script >minified

It takes two options:

-b Keep bang-comments (Comments starting with an exclamation mark) -p Force using the python implementation (not the C implementation)

The latest documentation is also available online at


No bugs, of course. ;-) But if you've found one or have an idea how to improve rjsmin, feel free to send a pull request on github or send a mail to


André "nd" Malo, GPG: 0x029C942244325167

If God intended people to be naked, they would be born that way. -- Oscar Wilde