UnderscoreJS 1.2.3 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 34705 bytes (33.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 12019 bytes (11.7k, 35%).

After GZIP compression these minified files vary in size:

Boot	4552 bytes (4.4k)	CDN
Baidu	4090 bytes (4.0k)	CDN
gzip -6 (default)	4076 bytes (4.0k)	local copy
gzip -9	4069 bytes (4.0k)	local copy
cdnjs	4067 bytes (4.0k)	CDN
unpkg	4052 bytes (4.0k)	CDN
libdeflate -12	3967 bytes (3.9k)	local copy
7zip -mx=9 -tgzip	3962 bytes (3.9k)	local copy
kzip -s0 -rn -b0	3961 bytes (3.9k)	local copy
zultra	3961 bytes (3.9k)	local copy
pigz -11 -n	3954 bytes (3.9k)	local copy
Zopfli	3945 bytes (3.9k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.3.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.2.3 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

Save 107 bytes by using my UnderscoreJS 1.2.3 Zopfli version instead of the best available CDN (2.71% smaller than unpkg, 3945 vs. 4052 bytes):

Download

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 --mls128 --bsr8 --lazy --ohh

(found September 17, 2015)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	128	--mls128
block splitting recursion	8	--bsr8
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/jashkenas/underscore/1.2.3/underscore-min.js --location | md5sum
eb40cdf14de93e997357c9c30017b2e6 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.3.min.zopfli.js.gz | md5sum
eb40cdf14de93e997357c9c30017b2e6 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.2.3/underscore-min.js --location | sha1sum
cfbc3fa20d685d100308e123c3310dc9600ef0fd -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.2.3.min.zopfli.js.gz | sha1sum
cfbc3fa20d685d100308e123c3310dc9600ef0fd -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	4552 bytes	eb40cdf14de93e997357c9c30017b2e6	(invalid)
cdnjs	4067 bytes	eb40cdf14de93e997357c9c30017b2e6	(invalid)
unpkg	4052 bytes	eb40cdf14de93e997357c9c30017b2e6	July 11, 2016 @ 16:49

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	4090 bytes	6a94c3bb265771bf56c49a692ef6f728	only whitespaces differ	(invalid)

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

Other Versions

Available UnderscoreJS versions at minime.stephan-brumme.com:

1.13.6, 1.13.5, 1.13.4, 1.13.3, 1.13.2, 1.13.1, 1.13.0,
1.12.1, 1.12.0,
1.11.0,
1.10.2, 1.10.1, 1.10.0,
1.9.2, 1.9.1, 1.9.0,
1.8.3, 1.8.2, 1.8.1,
1.7.0,
1.6.0,
1.5.2, 1.5.0,
1.4.4, 1.4.3, 1.4.2, 1.4.1, 1.4.0,
1.3.3, 1.3.2, 1.3.1, 1.3.0,
1.2.4, 1.2.3, 1.2.2, 1.2.1, 1.2.0,
1.1.7, 1.1.5, 1.1.4, 1.1.3, 1.1.2, 1.1.1, 1.1.0,
1.0.4, 1.0.3, 1.0.2, 1.0.1, 1.0.0,
0.6.0,
0.5.7, 0.5.6, 0.5.5, 0.5.4, 0.5.3, 0.5.2, 0.5.1, 0.5.0,
0.4.7, 0.4.6, 0.4.5, 0.4.4, 0.4.3, 0.4.2, 0.4.1, 0.4.0,
0.3.3, 0.3.2, 0.3.1, 0.3.0,
0.2.0,
0.1.1, 0.1.0

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, Socket.IO, ThreeJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
3945 bytes	-1 byte	zopfli --i100000 --mls128 --bsr8 --lazy --ohh	September 17, 2015 @ 17:03
3946 bytes	-2 bytes	zopfli --i1000 --mls4096 --bsr6 --lazy --ohh	September 8, 2015 @ 10:58
3948 bytes	–	zopfli --i100 --mls4096 --bsr6 --lazy --ohh	September 8, 2015 @ 10:34

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, 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	3951	3951	3951	3950	3951	3951	3950	3950	3950	3951	3951	3950	3949	3949	3949
4	3950	3950	3950	3949	3949	3949	3953	3945	3948	3950	3953	3949	3948	3949	3949
6	3949	3949	3949	3949	3949	3950	3948	3949	3948	3947	3950	3945	3947	3947	3947
7	3949	3949	3949	3945	3952	3949	3949	3945	3948	3950	3947	3948	3947	3950	3950
8	3950	3950	3949	3948	3949	3949	3945	3945	3949	3950	3948	3948	3947	3950	3950
9	3949	3949	3949	3948	3949	3949	3946	3945	3948	3950	3947	3947	3947	3947	3947
10	3949	3949	3950	3949	3950	3949	3949	3945	3948	3951	3947	3947	3947	3950	3950
11	3949	3949	3949	3949	3949	3949	3953	3945	3954	3950	3953	3947	3945	3945	3945
12	3949	3949	3949	3948	3950	3949	3945	3945	3948	3950	3947	3948	3948	3947	3947
13	3949	3949	3950	3949	3949	3949	3949	3948	3949	3950	3947	3947	3947	3947	3947
14	3949	3949	3949	3948	3949	3949	3953	3953	3948	3950	3953	3948	3947	3947	3947
15	3949	3949	3949	3949	3949	3949	3947	3947	3948	3950	3947	3947	3947	3950	3950
16	3953	3953	3953	3948	3949	3949	3947	3945	3949	3950	3948	3947	3947	3947	3947
17	3949	3949	3949	3949	3949	3949	3947	3946	3948	3950	3947	3947	3947	3947	3947
18	3949	3949	3949	3949	3950	3950	3947	3945	3947	3950	3947	3947	3947	3947	3947
19	3949	3949	3949	3949	3949	3951	3953	3945	3948	3950	3947	3947	3947	3947	3947
20	3949	3949	3949	3949	3950	3949	3947	3945	3947	3948	3947	3947	3947	3947	3947
21	3949	3949	3949	3949	3949	3950	3947	3945	3949	3950	3947	3947	3947	3947	3947
22	3949	3949	3949	3949	3950	3950	3949	3945	3948	3951	3947	3948	3948	3949	3949
23	3949	3949	3949	3949	3949	3949	3947	3945	3948	3950	3948	3948	3947	3947	3947
25	3949	3949	3950	3949	3950	3953	3949	3945	3950	3951	3949	3948	3947	3947	3947
30	3949	3949	3949	3949	3949	3949	3945	3945	3948	3947	3947	3948	3947	3947	3947
40	3949	3949	3949	3948	3949	3949	3949	3947	3949	3950	3947	3947	3948	3949	3949

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	3948 bytes	–	100%
1,000	3946 bytes	-2 bytes	100%
10,000	3946 bytes	–	100%
100,000	3945 bytes	-1 byte	16.23%
1,000,000	3945 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)	3961 bytes	+16 bytes (+0.41%)	–
1	3961 bytes	+16 bytes (+0.41%)	–
2	3981 bytes	+36 bytes (+0.91%)	+20 bytes
3	3979 bytes	+34 bytes (+0.86%)	+18 bytes
4	4010 bytes	+65 bytes (+1.65%)	+49 bytes
5	4033 bytes	+88 bytes (+2.23%)	+72 bytes
6	4065 bytes	+120 bytes (+3.04%)	+104 bytes
7	4091 bytes	+146 bytes (+3.70%)	+130 bytes
8	4124 bytes	+179 bytes (+4.54%)	+163 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	3539 bytes	-406 bytes (-10.29%)
Brotli (Wikipedia)	brotli	brotli -q 11	3630 bytes	-315 bytes (-7.98%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	3902 bytes	-43 bytes (-1.09%)
Zstandard (Wikipedia)	zstd	zstd -19	3978 bytes	+33 bytes (+0.84%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	4005 bytes	+60 bytes (+1.52%)
LZMA2 (Wikipedia)	xz	xz -9	4036 bytes	+91 bytes (+2.31%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	4398 bytes	+453 bytes (+11.48%)

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.