Socket.IO 1.7.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 211903 bytes (206.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 136467 bytes (133.3k, 64%).

After GZIP compression these minified files vary in size:

gzip -6 (default)	33146 bytes (32.4k)	local copy
gzip -9	32811 bytes (32.0k)	local copy
7zip -mx=9 -tgzip	31357 bytes (30.6k)	local copy
libdeflate -12	31346 bytes (30.6k)	local copy
zultra	31317 bytes (30.6k)	local copy
kzip -s0 -rn -b0	31273 bytes (30.5k)	local copy
pigz -11 -n	31256 bytes (30.5k)	local copy
Zopfli	31190 bytes (30.5k)	local copy
Boot	26210 bytes (25.6k)	CDN
cdnjs	22297 bytes (21.8k)	CDN

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/socketio/socket.io-1.7.1.min.js (or via HTTPS)

You will automatically get the smallest Socket.IO 1.7.1 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 --mls64 --bsr7 --lazy --ohh

(found September 8, 2017)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	64	--mls64
block splitting recursion	7	--bsr7
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/1.7.1/socket.io.min.js --location | md5sum
17f2479d908689a03381710c09495c65 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.7.1.min.zopfli.js.gz | md5sum
17f2479d908689a03381710c09495c65 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/socketio/socket.io-client/1.7.1/socket.io.min.js --location | sha1sum
98374695681c03f8ec512e1435a41de9bf8c2b52 -
curl --silent --compressed https://minime.stephan-brumme.com/files/socket.io/socket.io-1.7.1.min.zopfli.js.gz | sha1sum
98374695681c03f8ec512e1435a41de9bf8c2b52 -

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Boot	26210 bytes	8c95b98a636a39df32c396d665ef6908	< (function webpackUniversalModuleDefinition(root, factory) [...] < if(typeof exports === 'object' && typeof module === 'obje [...] < module.exports = factory(require("JSON")); < else if(typeof define === 'function' && define.amd) < define(["JSON"], factory); < else if(typeof exports === 'object') < exports["io"] = factory(require("JSON")); < else < root["io"] = factory(root["JSON"]); < })(this, function(__WEBPACK_EXTERNAL_MODULE_5__) { [...]	(invalid)
cdnjs	22297 bytes	8c95b98a636a39df32c396d665ef6908	< (function webpackUniversalModuleDefinition(root, factory) [...] < if(typeof exports === 'object' && typeof module === 'obje [...] < module.exports = factory(require("JSON")); < else if(typeof define === 'function' && define.amd) < define(["JSON"], factory); < else if(typeof exports === 'object') < exports["io"] = factory(require("JSON")); < else < root["io"] = factory(root["JSON"]); < })(this, function(__WEBPACK_EXTERNAL_MODULE_5__) { [...]	(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
31190 bytes	-3 bytes	zopfli --i1000000 --mls64 --bsr7 --lazy --ohh	September 8, 2017 @ 18:40
31193 bytes	-6 bytes	zopfli --i100000 --mls64 --bsr7 --lazy --ohh	September 7, 2017 @ 08:54
31199 bytes	-1 byte	zopfli --i1000 --mls4 --bsr4 --lazy --ohh	September 6, 2017 @ 14:58
31200 bytes	-2 bytes	zopfli --i1000 --mls2048 --bsr7 --lazy --ohh	September 6, 2017 @ 13:18
31202 bytes	-3 bytes	zopfli --i1000 --mls32 --bsr18 --lazy --ohh	September 6, 2017 @ 12:43
31205 bytes	–	zopfli --i100 --mls16384 --bsr16 --lazy --ohh	September 6, 2017 @ 11:37

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	31209	31209	31209	31211	31208	31209	31209	31209	31209	31209	31208	31208	31208	31209	31209
4	31200	31198	31199	31199	31201	31201	31201	31212	31200	31200	31200	31199	31198	31201	31207
6	31200	31200	31211	31200	31200	31201	31201	31200	31200	31200	31200	31207	31201	31198	31200
7	31202	31200	31201	31201	31201	31190	31201	31200	31198	31200	31199	31203	31199	31201	31206
8	31200	31201	31200	31200	31200	31201	31201	31196	31200	31200	31201	31208	31199	31200	31208
9	31200	31201	31200	31200	31201	31200	31201	31200	31198	31200	31201	31200	31197	31198	31204
10	31200	31200	31199	31200	31201	31201	31198	31200	31196	31199	31201	31200	31197	31201	31206
11	31201	31199	31199	31200	31201	31201	31207	31194	31198	31200	31201	31207	31200	31206	31206
12	31200	31201	31208	31199	31207	31199	31207	31201	31200	31200	31201	31200	31200	31202	31208
13	31200	31201	31201	31198	31200	31200	31201	31201	31200	31200	31201	31200	31201	31200	31208
14	31200	31200	31200	31200	31207	31200	31202	31200	31198	31200	31199	31200	31200	31200	31208
15	31201	31201	31201	31201	31200	31195	31201	31200	31199	31200	31199	31200	31200	31198	31208
16	31200	31200	31199	31202	31201	31201	31201	31199	31200	31201	31199	31199	31200	31199	31206
17	31200	31200	31199	31201	31201	31201	31198	31200	31198	31199	31201	31200	31200	31200	31206
18	31200	31200	31201	31201	31201	31200	31207	31200	31198	31199	31199	31201	31200	31198	31206
19	31200	31200	31200	31200	31201	31198	31198	31200	31200	31200	31201	31200	31197	31198	31207
20	31200	31200	31200	31201	31200	31201	31200	31200	31200	31200	31200	31201	31199	31200	31208
21	31201	31200	31200	31201	31200	31201	31201	31200	31199	31201	31199	31200	31197	31200	31206
22	31200	31200	31201	31201	31200	31200	31201	31198	31200	31200	31200	31201	31200	31198	31206
23	31201	31200	31201	31200	31201	31195	31200	31200	31199	31200	31200	31198	31201	31200	31206
25	31200	31200	31200	31201	31201	31200	31201	31200	31200	31200	31200	31199	31201	31195	31206
30	31202	31201	31199	31200	31200	31202	31200	31201	31200	31200	31199	31200	31199	31195	31206
40	31200	31200	31199	31200	31201	31201	31201	31200	31198	31200	31199	31198	31200	31200	31206

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	31205 bytes	–	100%
1,000	31199 bytes	-6 bytes	100%
10,000	31194 bytes	-5 bytes	100%
100,000	31193 bytes	-1 byte	2.32%
1,000,000	31190 bytes	-3 bytes	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)	31273 bytes	+83 bytes (+0.27%)	–
1	31286 bytes	+96 bytes (+0.31%)	+13 bytes
2	31328 bytes	+138 bytes (+0.44%)	+55 bytes
3	31358 bytes	+168 bytes (+0.54%)	+85 bytes
4	31331 bytes	+141 bytes (+0.45%)	+58 bytes
5	31371 bytes	+181 bytes (+0.58%)	+98 bytes
6	31392 bytes	+202 bytes (+0.65%)	+119 bytes
7	31392 bytes	+202 bytes (+0.65%)	+119 bytes
8	31437 bytes	+247 bytes (+0.79%)	+164 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	22831 bytes	-8359 bytes (-26.80%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	23909 bytes	-7281 bytes (-23.34%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	26066 bytes	-5124 bytes (-16.43%)
Brotli (Wikipedia)	brotli	brotli -q 11	27000 bytes	-4190 bytes (-13.43%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	27293 bytes	-3897 bytes (-12.49%)
LZMA2 (Wikipedia)	xz	xz -9	28404 bytes	-2786 bytes (-8.93%)
Zstandard (Wikipedia)	zstd	zstd -19	29038 bytes	-2152 bytes (-6.90%)

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.