UnderscoreJS 1.0.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 24686 bytes (24.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 8617 bytes (8.4k, 35%).

After GZIP compression these minified files vary in size:

Boot	3247 bytes (3.2k)	CDN
gzip -6 (default)	2964 bytes (2.9k)	local copy
Baidu	2961 bytes (2.9k)	CDN
gzip -9	2957 bytes (2.9k)	local copy
cdnjs	2948 bytes (2.9k)	CDN
libdeflate -12	2864 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2862 bytes (2.8k)	local copy
kzip -s0 -rn -b0	2861 bytes (2.8k)	local copy
pigz -11 -n	2860 bytes (2.8k)	local copy
zultra	2859 bytes (2.8k)	local copy
Zopfli	2858 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.0.0 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 90 bytes by using my UnderscoreJS 1.0.0 Zopfli version instead of the best available CDN (3.15% smaller than cdnjs, 2858 vs. 2948 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 --i1000 --mb8 --mls8192 --bsr23 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	1000	--i1000
maximum blocks	8	--mb8
maximum length score	8192	--mls8192
block splitting recursion	23	--bsr23
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/1.0.0/underscore-min.js --location | md5sum
da836e0cccc9e03205b48ffe4c509411 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.0.min.zopfli.js.gz | md5sum
da836e0cccc9e03205b48ffe4c509411 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.0.0/underscore-min.js --location | sha1sum
ad0775c89a87111019840dc7bbf902d832e4ccdf -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.0.min.zopfli.js.gz | sha1sum
ad0775c89a87111019840dc7bbf902d832e4ccdf -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3247 bytes	da836e0cccc9e03205b48ffe4c509411	(invalid)
cdnjs	2948 bytes	da836e0cccc9e03205b48ffe4c509411	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2961 bytes	dd705e1f9d996a49f40f6ce161d75e65	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
2858 bytes	-1 byte	zopfli --i1000 --mls8192 --bsr23 --lazy --ohh	February 2, 2016 @ 19:07
2859 bytes	–	zopfli --i100 --mls8192 --bsr23 --lazy --ohh	February 2, 2016 @ 19:06

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 @ 12:47.

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:
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	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
4	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
6	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
7	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
8	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
9	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
10	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
11	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
12	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
13	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
14	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
15	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
16	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
17	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
18	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
19	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
20	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
21	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
22	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
23	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
25	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
30	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858
40	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858	2858

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	2859 bytes	–	100%
1,000	2858 bytes	-1 byte	100%
10,000	2858 bytes	–	100%
100,000	2858 bytes	–	100%
1,000,000	2858 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)	2861 bytes	+3 bytes (+0.10%)	–
1	2861 bytes	+3 bytes (+0.10%)	–
2	2892 bytes	+34 bytes (+1.19%)	+31 bytes
3	2926 bytes	+68 bytes (+2.38%)	+65 bytes
4	2939 bytes	+81 bytes (+2.83%)	+78 bytes
5	2970 bytes	+112 bytes (+3.92%)	+109 bytes
6	3004 bytes	+146 bytes (+5.11%)	+143 bytes
7	3039 bytes	+181 bytes (+6.33%)	+178 bytes
8	3073 bytes	+215 bytes (+7.52%)	+212 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	2572 bytes	-286 bytes (-10.01%)
Brotli (Wikipedia)	brotli	brotli -q 11	2657 bytes	-201 bytes (-7.03%)
Zstandard (Wikipedia)	zstd	zstd -19	2876 bytes	+18 bytes (+0.63%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2900 bytes	+42 bytes (+1.47%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2912 bytes	+54 bytes (+1.89%)
LZMA2 (Wikipedia)	xz	xz -9	2948 bytes	+90 bytes (+3.15%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3453 bytes	+595 bytes (+20.82%)

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.