mincss

About

mincss is an extendible CSS minifier written in OCaml. It features a complete parser for the CSS3 language, along with type definitions that are consistent with the official CSS specification and a traversal utility function for use in transformation passes.

Installation

For now, there is no easy installation option for mincss (yet). An up-to-date 64-bit ELF binary is available for download here. You can also build the binary from source (see Building mincss below).

Features

Whitespace compression

a,                                  |  a,.myclass [class~="foo"]>p{color:#fff}
.myclass [class ~= "foo"] >  p {    |
    color: #fff;                    |
}                                   |

Compression of simple expressions

color: rgb(257, -2, 0);             |  color: red;
color: rgb(67%, 67.5%, 68%);        |  color: #abacad;
color: #aaffbb;                     |  color: #afb;
color: white;                       |  color: #fff;
font-weight: normal;                |  font-weight: 400;

Generation of shorthand properties

font-weight: normal;                |  font: normal 12px/15px sans-serif;
font-size: 12px;                    |
line-height: 15px;                  |
font-family: sans-serif;            |

Any existing shorthands are first unfolded into their non-shorthand counterparts, after which the last value is used for shorthand generation:

font: normal 12px/15px sans-serif;  |  font: bold 12px/15px sans-serif;
font-weight: bold;                  |

Pruning duplicate declarations

color: #000;                        |  color: #fff;
color: #fff;                        |

Note that !important annotations are correctly handled:

color: #eee !important;             |  color: #000 !important;
color: #000 !important;             |
color: #fff;                        |

Sorting declarations

The --sort command-line option sorts declarations alphabetically. This option is disabled by default since it does not affect file size.

Command-line interface

Output of mincss -h:

Usage: ./mincss [<options>] [<file> ...]

Generic options:
 -h, --help        Show this help message
 -v, --verbose     Verbose mode: show compression rate
 -o <file>         Output file (defaults to stdout)
 <file> ...        Input files (default is to read from stdin)

Optimization flags (if none are specified, all are enabled):
 -w, --whitespace  Eliminate unnecessary whitespaces (has the greatest effect, omit for pretty-printing)
 -c, --simple      Shorten colors and font weights
 -s, --shorthands  Generate shorthand properties
 -d, --duplicates  Prune duplicate properties (WARNING: may affect cross-browser hacks)
 -p, --pretty      Shorthand for -c -s -d
 -e, --echo        Just parse and pretty-print, no optimizations

Formatting options:
 --sort            Sort declarations in each selector group

Building mincss

Dependencies are OCaml 4.0 and menhir.

Bootstrapping on a Debian system can be done as follows:

$ sudo apt-get install ocaml opam git
$ opam init
$ opam switch 4.01.0
$ opam install menhir
$ git clone git@github.com:taddeus/mincss.git
$ cd mincss
$ make
$ ./mincss --help

TODO / bugs

• border shorthand generation produces out-of-order results when direction-specific declarations follow a generic border declaration. This produces inequivalent CSS, and could be fixed by unfolding each generic border declaration into four direction-specific ones, and sybsequently generating the shortest possible representation of the resulting box model.
• border:none could be border:0, or in general any shorthand that has both a style and width property should be transformed from none into 0.