Socket.IO 1.3.2 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 172531 bytes (168.5k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 90645 bytes (88.5k, 53%).

After GZIP compression these minified files vary in size:

Boot	23650 bytes (23.1k)	CDN
gzip -6 (default)	23606 bytes (23.1k)	local copy
gzip -9	23508 bytes (23.0k)	local copy
libdeflate -12	22670 bytes (22.1k)	local copy
7zip -mx=9 -tgzip	22643 bytes (22.1k)	local copy
zultra	22643 bytes (22.1k)	local copy
kzip -s0 -rn -b2	22608 bytes (22.1k)	local copy
pigz -11 -n	22603 bytes (22.1k)	local copy
Zopfli	22584 bytes (22.1k)	local copy
cdnjs	20261 bytes (19.8k)	CDN

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.3.2.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.3.2 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 --i100000 --mb8 --mls2048 --bsr11 --lazy --ohh

(found June 30, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	2048	--mls2048
block splitting recursion	11	--bsr11
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/1.3.2/socket.io.min.js --location | md5sum
3e618f924c63851dce1372ddefc2c5ec -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.3.2.min.zopfli.js.gz | md5sum
3e618f924c63851dce1372ddefc2c5ec -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.3.2/socket.io.min.js --location | sha1sum
c894b0c8854b493d1b041ce22365ebcde837815f -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.3.2.min.zopfli.js.gz | sha1sum
c894b0c8854b493d1b041ce22365ebcde837815f -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	23650 bytes	45dbaf4089495584b97f030ea958da2f	< !function(e){if("object"==typeof exports&&"undefined"!=typ [...] < this.query=this.query\|\|{};if(!callbacks){if(!global.___eio [...] < byteString+=encodeCodePoint(codePoint)}return byteString}f [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > (!c\|\|e)&&(this.supportsBinary=!1),r.call(this,t)}var r=t(" [...] > });return n.call(t,e,o)};u.parse=function(t,e){var n,r;ret [...]	(invalid)
cdnjs	20261 bytes	45dbaf4089495584b97f030ea958da2f	< !function(e){if("object"==typeof exports&&"undefined"!=typ [...] < this.query=this.query\|\|{};if(!callbacks){if(!global.___eio [...] < byteString+=encodeCodePoint(codePoint)}return byteString}f [...] > !function(t){if("object"==typeof exports&&"undefined"!=typ [...] > (!c\|\|e)&&(this.supportsBinary=!1),r.call(this,t)}var r=t(" [...] > });return n.call(t,e,o)};u.parse=function(t,e){var n,r;ret [...]	(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
22584 bytes	-1 byte	zopfli --i100000 --mls2048 --bsr11 --lazy --ohh	June 30, 2016 @ 09:44
22585 bytes	-1 byte	zopfli --i10000 --mls2048 --bsr11 --lazy --ohh	June 30, 2016 @ 08:03
22586 bytes	-3 bytes	zopfli --i1000 --mls2048 --bsr11 --lazy --ohh	June 29, 2016 @ 19:46
22589 bytes	-1 byte	zopfli --i10000 --mls512 --bsr18 --lazy --ohh	June 29, 2016 @ 17:05
22590 bytes	-1 byte	zopfli --i1000 --mls1024 --bsr15 --lazy --ohh	June 29, 2016 @ 15:25
22591 bytes	–	zopfli --i100 --mls1024 --bsr15 --lazy --ohh	June 29, 2016 @ 12:29

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 @ 12:55.

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 or 100,000.

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	22593	22593	22594	22601	22603	22603	22592	22592	22591	22592	22594	22603	22606	22607	22605
4	22604	22618	22617	22620	22621	22599	22600	22600	22590	22594	22591	22607	22604	22605	22605
6	22591	22590	22590	22591	22592	22592	22591	22591	22591	22590	22589	22605	22606	22604	22606
7	22593	22597	22590	22594	22590	22592	22592	22592	22589	22589	22594	22604	22606	22605	22603
8	22591	22590	22589	22589	22590	22590	22588	22591	22590	22590	22594	22604	22606	22605	22605
9	22591	22591	22598	22598	22597	22599	22601	22591	22590	22589	22590	22603	22605	22605	22605
10	22593	22597	22599	22589	22590	22595	22589	22597	22591	22590	22594	22604	22605	22605	22606
11	22592	22587	22590	22592	22589	22596	22592	22597	22589	22593	22584	22604	22603	22605	22606
12	22594	22599	22599	22602	22600	22596	22599	22590	22590	22590	22589	22604	22602	22605	22604
13	22589	22590	22587	22591	22589	22591	22590	22591	22590	22590	22589	22603	22606	22605	22609
14	22590	22590	22589	22591	22593	22591	22589	22589	22590	22590	22590	22602	22603	22610	22609
15	22595	22588	22590	22590	22591	22592	22592	22593	22589	22588	22591	22604	22605	22605	22604
16	22588	22587	22599	22599	22591	22597	22596	22596	22591	22589	22591	22605	22603	22603	22605
17	22590	22590	22588	22589	22590	22590	22589	22590	22590	22590	22591	22604	22605	22605	22609
18	22590	22589	22590	22589	22590	22590	22589	22589	22589	22589	22590	22605	22604	22605	22604
19	22590	22590	22588	22588	22591	22590	22589	22591	22590	22590	22591	22603	22605	22607	22605
20	22589	22598	22598	22599	22602	22598	22597	22598	22590	22588	22590	22605	22605	22607	22604
21	22590	22590	22599	22600	22601	22598	22589	22590	22590	22588	22590	22604	22607	22607	22605
22	22589	22588	22588	22589	22589	22591	22590	22589	22590	22590	22590	22604	22603	22607	22607
23	22591	22590	22590	22589	22591	22590	22589	22589	22590	22589	22590	22604	22606	22605	22605
25	22590	22600	22599	22597	22600	22597	22599	22591	22591	22589	22590	22602	22607	22605	22606
30	22593	22594	22600	22598	22598	22597	22588	22589	22591	22589	22591	22604	22605	22605	22606
40	22589	22599	22598	22590	22588	22590	22590	22591	22590	22591	22591	22602	22606	22604	22603

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	22591 bytes	–	100%
1,000	22586 bytes	-5 bytes	100%
10,000	22585 bytes	-1 byte	100%
100,000	22584 bytes	-1 byte	0.29%
1,000,000	–	–	–
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)	22610 bytes	+26 bytes (+0.12%)	+2 bytes
1	22626 bytes	+42 bytes (+0.19%)	+18 bytes
2	22608 bytes	+24 bytes (+0.11%)	–
3	22651 bytes	+67 bytes (+0.30%)	+43 bytes
4	22683 bytes	+99 bytes (+0.44%)	+75 bytes
5	22714 bytes	+130 bytes (+0.58%)	+106 bytes
6	22749 bytes	+165 bytes (+0.73%)	+141 bytes
7	22775 bytes	+191 bytes (+0.85%)	+167 bytes
8	22781 bytes	+197 bytes (+0.87%)	+173 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
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	18266 bytes	-4318 bytes (-19.12%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	19273 bytes	-3311 bytes (-14.66%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	20142 bytes	-2442 bytes (-10.81%)
Brotli (Wikipedia)	brotli	brotli -q 11	21334 bytes	-1250 bytes (-5.53%)
LZMA2 (Wikipedia)	xz	xz -9	22056 bytes	-528 bytes (-2.34%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	22247 bytes	-337 bytes (-1.49%)
Zstandard (Wikipedia)	zstd	zstd -19	22385 bytes	-199 bytes (-0.88%)

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.