Socket.IO 1.4.4 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 184588 bytes (180.3k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 97657 bytes (95.4k, 53%).

After GZIP compression these minified files vary in size:

Boot	30573 bytes (29.9k)	CDN
cdnjs	25672 bytes (25.1k)	CDN
gzip -6 (default)	25458 bytes (24.9k)	local copy
gzip -9	25343 bytes (24.7k)	local copy
libdeflate -12	24458 bytes (23.9k)	local copy
7zip -mx=9 -tgzip	24451 bytes (23.9k)	local copy
zultra	24419 bytes (23.8k)	local copy
kzip -s0 -rn -b2	24400 bytes (23.8k)	local copy
pigz -11 -n	24398 bytes (23.8k)	local copy
Zopfli	24378 bytes (23.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.4.4.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.4.4 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 --i100000 --mb8 --mls1024 --bsr15 --lazy --ohh

(found July 1, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
block splitting recursion	15	--bsr15
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/1.4.4/socket.io.min.js --location | md5sum
154157e30bbf780a4564b84dcde03254 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.4.min.zopfli.js.gz | md5sum
154157e30bbf780a4564b84dcde03254 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.4.4/socket.io.min.js --location | sha1sum
89bdaa254c5fd0c22b9c4ba6e9dfc54d99da99b2 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.4.4.min.zopfli.js.gz | sha1sum
89bdaa254c5fd0c22b9c4ba6e9dfc54d99da99b2 -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	30573 bytes	f602f8eb1dfe8e6c3daff2229093a7ab	< base64+=chars[(bytes[i+1]&15)<<2\|bytes[i+2]>>6];base64+=ch [...] < });if(this.autoConnect){onConnecting()}}function onConnect [...] < if(element===undef){delete source[property]}else{source[pr [...] > base64+=chars[(bytes[i+1]&15)<<2\|bytes[i+2]>>6];base64+=ch [...] > socket.id=self.engine.id});if(this.autoConnect){onConnecti [...] > };var update=function(source,property,callback){var elemen [...]	(invalid)
cdnjs	25672 bytes	f602f8eb1dfe8e6c3daff2229093a7ab	< base64+=chars[(bytes[i+1]&15)<<2\|bytes[i+2]>>6];base64+=ch [...] < });if(this.autoConnect){onConnecting()}}function onConnect [...] < if(element===undef){delete source[property]}else{source[pr [...] > base64+=chars[(bytes[i+1]&15)<<2\|bytes[i+2]>>6];base64+=ch [...] > socket.id=self.engine.id});if(this.autoConnect){onConnecti [...] > };var update=function(source,property,callback){var elemen [...]	(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
24378 bytes	-1 byte	zopfli --i100000 --mls1024 --bsr15 --lazy --ohh	July 1, 2016 @ 10:39
24379 bytes	-4 bytes	zopfli --i10000 --mls1024 --bsr15 --lazy --ohh	June 29, 2016 @ 17:31
24383 bytes	-2 bytes	zopfli --i1000 --mls1024 --bsr15 --lazy --ohh	June 29, 2016 @ 16:01
24385 bytes	-3 bytes	zopfli --i1000 --mls128 --bsr11 --lazy --ohh	June 29, 2016 @ 15:34
24388 bytes	–	zopfli --i100 --mls128 --bsr11 --lazy --ohh	June 29, 2016 @ 13:21

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 @ 12:48.

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	24392	24393	24392	24393	24400	24400	24391	24392	24393	24393	24393	24395	24392	24392	24391
4	24390	24393	24392	24391	24389	24388	24386	24385	24386	24392	24388	24391	24387	24389	24390
6	24396	24391	24392	24384	24386	24388	24395	24391	24401	24392	24392	24392	24387	24390	24389
7	24396	24394	24383	24383	24396	24384	24387	24380	24394	24390	24391	24391	24387	24390	24395
8	24390	24381	24390	24383	24385	24385	24385	24392	24381	24380	24387	24393	24394	24390	24390
9	24394	24396	24393	24398	24395	24384	24388	24392	24385	24381	24390	24391	24388	24390	24390
10	24389	24392	24387	24391	24385	24388	24385	24385	24387	24391	24392	24388	24387	24390	24388
11	24387	24385	24390	24387	24388	24383	24384	24385	24388	24387	24392	24391	24387	24390	24390
12	24394	24378	24390	24383	24387	24384	24384	24381	24383	24391	24382	24391	24383	24389	24388
13	24386	24388	24391	24393	24395	24394	24387	24380	24395	24391	24392	24391	24387	24390	24388
14	24394	24391	24393	24394	24384	24384	24391	24388	24383	24391	24391	24392	24388	24390	24390
15	24395	24392	24397	24389	24386	24383	24388	24390	24391	24378	24387	24391	24387	24390	24390
16	24395	24395	24395	24393	24384	24390	24388	24386	24382	24381	24381	24391	24393	24390	24390
17	24389	24395	24395	24387	24384	24389	24387	24386	24384	24392	24387	24391	24387	24390	24390
18	24394	24393	24391	24382	24397	24386	24388	24392	24380	24391	24382	24391	24395	24389	24388
19	24394	24394	24395	24393	24395	24386	24392	24392	24384	24391	24382	24391	24394	24390	24388
20	24394	24392	24394	24396	24399	24393	24390	24383	24384	24381	24392	24393	24393	24390	24390
21	24394	24395	24395	24383	24398	24385	24391	24391	24384	24380	24384	24392	24388	24390	24389
22	24392	24395	24396	24387	24383	24384	24384	24392	24384	24380	24382	24391	24394	24390	24388
23	24394	24393	24397	24388	24384	24394	24387	24388	24381	24391	24382	24390	24387	24390	24388
25	24396	24395	24395	24382	24397	24388	24385	24381	24380	24380	24392	24391	24387	24390	24387
30	24395	24394	24395	24389	24394	24385	24390	24392	24384	24391	24388	24391	24387	24390	24390
40	24393	24393	24394	24395	24395	24383	24382	24388	24383	24379	24388	24392	24388	24389	24387

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	24388 bytes	–	100%
1,000	24381 bytes	-7 bytes	100%
10,000	24379 bytes	-2 bytes	100%
100,000	24378 bytes	-1 byte	0.87%
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)	24421 bytes	+43 bytes (+0.18%)	+21 bytes
1	24418 bytes	+40 bytes (+0.16%)	+18 bytes
2	24400 bytes	+22 bytes (+0.09%)	–
3	24436 bytes	+58 bytes (+0.24%)	+36 bytes
4	24461 bytes	+83 bytes (+0.34%)	+61 bytes
5	24497 bytes	+119 bytes (+0.49%)	+97 bytes
6	24526 bytes	+148 bytes (+0.61%)	+126 bytes
7	24554 bytes	+176 bytes (+0.72%)	+154 bytes
8	24594 bytes	+216 bytes (+0.89%)	+194 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	19205 bytes	-5173 bytes (-21.22%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	20393 bytes	-3985 bytes (-16.35%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	22090 bytes	-2288 bytes (-9.39%)
Brotli (Wikipedia)	brotli	brotli -q 11	22527 bytes	-1851 bytes (-7.59%)
LZMA2 (Wikipedia)	xz	xz -9	23288 bytes	-1090 bytes (-4.47%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	23579 bytes	-799 bytes (-3.28%)
Zstandard (Wikipedia)	zstd	zstd -19	23689 bytes	-689 bytes (-2.83%)

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.