Socket.IO 2.0.4 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 60730 bytes (59.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 52419 bytes (51.2k, 86%).

After GZIP compression these minified files vary in size:

Boot	18502 bytes (18.1k)	CDN
cdnjs	15682 bytes (15.3k)	CDN
gzip -6 (default)	15524 bytes (15.2k)	local copy
gzip -9	15460 bytes (15.1k)	local copy
libdeflate -12	14939 bytes (14.6k)	local copy
7zip -mx=9 -tgzip	14912 bytes (14.6k)	local copy
kzip -s0 -rn -b4	14900 bytes (14.6k)	local copy
zultra	14889 bytes (14.5k)	local copy
pigz -11 -n	14870 bytes (14.5k)	local copy
Zopfli	14849 bytes (14.5k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-2.0.4.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 2.0.4 file, ETag caching is available and
if your browser doesn't support GZIP decompression then the uncompressed version will be sent.

Currently best Zopfli settings

You can use my super-compressed files for whatever purpose you like as long as you respect the library's original license agreement.
There are no restrictions from my side - but please avoid hot-linking if you run a high-traffic website.

These command-line settings yielded the best compression ratio so far (Linux version of zopfli-krzymod):
zopfli --i1000000 --mb8 --mls128 --bsr18 --lazy --ohh

(found October 23, 2017)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	128	--mls128
block splitting recursion	18	--bsr18
lazy matching in LZ77	yes	--lazy
optimized Huffman headers	yes	--ohh
initial random W for iterations	1	--rw1
initial random Z for iterations	2	--rz2

Verify file integrity

After decompression, my uncompressed files are identical to the original ones:

MD5:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/2.0.4/socket.io.min.js --location | md5sum
d36d8ec02255a85e55e9d951e977e402 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-2.0.4.min.zopfli.js.gz | md5sum
d36d8ec02255a85e55e9d951e977e402 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/2.0.4/socket.io.min.js --location | sha1sum
c6c00e3a418b10284a0728f305c8ac29604150fc -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-2.0.4.min.zopfli.js.gz | sha1sum
c6c00e3a418b10284a0728f305c8ac29604150fc -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	18502 bytes	d36d8ec02255a85e55e9d951e977e402	November 14, 2017 @ 18:05
cdnjs	15682 bytes	d36d8ec02255a85e55e9d951e977e402	(invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available Socket.IO versions at minime.stephan-brumme.com:

4.5.4, 4.5.3, 4.5.2, 4.5.1, 4.5.0, 4.4.1, 4.4.0, 4.3.2, 4.3.1, 4.3.0, 4.2.0, 4.1.3, 4.1.2, 4.1.1, 4.1.0, 4.0.2, 4.0.1, 4.0.0,
3.1.2, 3.1.1, 3.1.0, 3.0.5, 3.0.4, 3.0.3, 3.0.2, 3.0.1, 3.0.0,
2.4.0, 2.3.1, 2.3.0, 2.2.0, 2.1.1, 2.1.0, 2.0.4, 2.0.3, 2.0.2, 2.0.1, 2.0.0,
1.7.4, 1.7.2, 1.7.1, 1.7.0, 1.6.0, 1.5.0, 1.4.5, 1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0, 1.3.7, 1.3.6, 1.3.5, 1.3.4, 1.3.3, 1.3.2, 1.3.1, 1.3.0, 1.2.1, 1.2.0, 1.1.0, 1.0.6, 1.0.5, 1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, Bootstrap, D3, Dojo, Ember, jQuery, Knockout, lodash, React, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
14849 bytes	-1 byte	zopfli --i1000000 --mls128 --bsr18 --lazy --ohh	October 23, 2017 @ 17:56
14850 bytes	-1 byte	zopfli --i10000 --mls128 --bsr18 --lazy --ohh	October 23, 2017 @ 15:11
14851 bytes	-2 bytes	zopfli --i10000 --mls2 --bsr40 --lazy --ohh	October 23, 2017 @ 15:00
14853 bytes	-1 byte	zopfli --i10000 --mls128 --bsr9 --lazy --ohh	October 23, 2017 @ 14:54
14854 bytes	-1 byte	zopfli --i1000 --mls128 --bsr9 --lazy --ohh	October 23, 2017 @ 14:41
14855 bytes	-1 byte	zopfli --i1000 --mls4 --bsr8 --lazy --ohh	October 23, 2017 @ 14:35
14856 bytes	–	zopfli --i100 --mls512 --bsr30 --lazy --ohh	October 23, 2017 @ 14:29

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on July 20, 2020 @ 12:54.

Heatmaps

This Zopfli heatmap visualizes how compression changes when modifying the --bsr and --mls parameter.
Cell's contents is the best filesize achieved (in bytes, hover with mouse over cells to see number of iterations).

Good parameters are green, bad are red. The best and worst are bold as well.
The brightness of the blue background color indicates how many iterations were processed:
10,000, 100,000 or 1,000,000.

bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
bsr \ mls	2	4	8	16	32	64	128	256	512	1024	2048	4096	8192	16384	32768
2	14864	14863	14864	14862	14864	14863	14862	14862	14861	14877	14877	14876	14877	14870	14874
4	14865	14853	14864	14864	14863	14863	14864	14854	14863	14860	14874	14875	14878	14864	14860
6	14859	14858	14857	14858	14854	14859	14855	14861	14860	14871	14872	14876	14861	14857	14857
7	14855	14857	14854	14856	14854	14854	14855	14854	14862	14872	14873	14872	14863	14853	14859
8	14865	14854	14855	14853	14855	14862	14855	14860	14861	14871	14872	14873	14876	14853	14868
9	14854	14860	14859	14853	14855	14854	14853	14855	14871	14862	14874	14876	14864	14858	14857
10	14856	14858	14855	14853	14856	14858	14854	14858	14857	14872	14858	14872	14876	14855	14859
11	14854	14863	14855	14854	14854	14863	14853	14857	14864	14872	14874	14873	14876	14861	14868
12	14852	14853	14854	14855	14854	14857	14851	14857	14857	14872	14873	14871	14863	14857	14859
13	14858	14857	14858	14862	14854	14857	14852	14854	14859	14864	14872	14873	14864	14857	14868
14	14854	14858	14854	14854	14855	14851	14853	14864	14858	14863	14872	14872	14861	14854	14868
15	14854	14857	14854	14854	14854	14854	14855	14854	14862	14872	14856	14873	14864	14854	14859
16	14859	14855	14857	14853	14854	14855	14854	14855	14860	14872	14873	14873	14875	14857	14868
17	14854	14854	14858	14860	14852	14862	14855	14857	14859	14863	14872	14872	14860	14856	14862
18	14852	14854	14855	14854	14852	14851	14849	14854	14861	14872	14870	14872	14862	14851	14868
19	14854	14857	14853	14853	14853	14858	14856	14859	14859	14872	14873	14872	14876	14856	14859
20	14854	14857	14853	14854	14853	14863	14851	14857	14859	14863	14870	14872	14877	14859	14858
21	14854	14857	14859	14854	14858	14853	14857	14854	14859	14871	14872	14871	14875	14853	14868
22	14855	14853	14855	14862	14853	14853	14851	14854	14862	14872	14872	14871	14877	14858	14868
23	14852	14857	14855	14854	14854	14861	14853	14858	14863	14871	14873	14873	14876	14854	14858
25	14855	14856	14856	14853	14855	14864	14853	14857	14862	14871	14857	14861	14860	14857	14859
30	14854	14855	14857	14853	14855	14851	14853	14857	14853	14872	14872	14872	14863	14854	14867
40	14851	14856	14858	14853	14855	14854	14856	14855	14866	14862	14873	14877	14877	14851	14866

Due to the Monte Carlo design of my search algorithm, not all parameters have reached the same number of iterations yet:

Iterations	Min. Bytes	Reduction	Coverage
100	14856 bytes	–	100%
1,000	14854 bytes	-2 bytes	100%
10,000	14850 bytes	-4 bytes	100%
100,000	14850 bytes	–	0.58%
1,000,000	14849 bytes	-1 byte	0.29%
10,000,000	–	–	–

KZIP has far less options available for tuning/optimization. I only played around with the number of blocks (parameter -n):

Blocks	Min. Bytes	Compared To Best Zopfli	Compared To Best KZIP
(any)	14914 bytes	+65 bytes (+0.44%)	+14 bytes
1	14914 bytes	+65 bytes (+0.44%)	+14 bytes
2	14915 bytes	+66 bytes (+0.44%)	+15 bytes
3	14936 bytes	+87 bytes (+0.59%)	+36 bytes
4	14900 bytes	+51 bytes (+0.34%)	–
5	14917 bytes	+68 bytes (+0.46%)	+17 bytes
6	14949 bytes	+100 bytes (+0.67%)	+49 bytes
7	14986 bytes	+137 bytes (+0.92%)	+86 bytes
8	15017 bytes	+168 bytes (+1.13%)	+117 bytes

Non-DEFLATE Algorithms

Archivers based on completely different compression algorithms often produce superior results.
Unfortunately, browsers only support gzip compression at the moment.
However, support for Brotli is constantly growing - for example, your browser actually supports it !

Algorithm	Program	Parameters	Size	Compared To Best Zopfli
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	12433 bytes	-2416 bytes (-16.27%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	12616 bytes	-2233 bytes (-15.04%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	13696 bytes	-1153 bytes (-7.76%)
Brotli (Wikipedia)	brotli	brotli -q 11	13746 bytes	-1103 bytes (-7.43%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	14198 bytes	-651 bytes (-4.38%)
LZMA2 (Wikipedia)	xz	xz -9	14452 bytes	-397 bytes (-2.67%)
Zstandard (Wikipedia)	zstd	zstd -19	14687 bytes	-162 bytes (-1.09%)

Detailled Analysis

I wrote a DEFLATE decoder in Javascript. Click the button below to start a client-side analysis of the smallest gzipped files (may take a second):

Load and Parse Data

Notes: pigz is a fast open source multi-threaded implementation of gzip written by one of the original authors of gzip.
However, when using compression level 11, pigz actually switches to the slower Zopfli algorithm and isn't multi-threaded anymore.
KrzyMOD's extensions to Zopfli offer the highest level of configuration and is therefore used for my brute-force search.
Ken Silverman wrote the closed-source KZIP compression program and Jonathon Fowler ported it to Linux.
Defluff was created by Joachim Henke; DeflOpt is a tool by Ben Jos Walbeehm.

website made by Stephan Brumme in 2015 and still improving in 2026.
all timestamps are displayed in central european time. see my changelog.
no flash, not even images or external css files - and everything squeezed into a single html file.
which was handsomely compressed before releasing it into the wild internet - obviously.

please visit my homepage and my blog, too.
email: minime (at) stephan-brumme.com

All trademarks are property of their respective owners. You know, the boring legal stuff.