UnderscoreJS 1.0.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 24701 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 8628 bytes (8.4k, 35%).

After GZIP compression these minified files vary in size:

Boot	3253 bytes (3.2k)	CDN
gzip -6 (default)	2971 bytes (2.9k)	local copy
Baidu	2967 bytes (2.9k)	CDN
gzip -9	2964 bytes (2.9k)	local copy
cdnjs	2954 bytes (2.9k)	CDN
libdeflate -12	2870 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2869 bytes (2.8k)	local copy
zultra	2869 bytes (2.8k)	local copy
kzip -s0 -rn -b0	2867 bytes (2.8k)	local copy
pigz -11 -n	2866 bytes (2.8k)	local copy
Zopfli	2864 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.0.1 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

Save 90 bytes by using my UnderscoreJS 1.0.1 Zopfli version instead of the best available CDN (3.14% smaller than cdnjs, 2864 vs. 2954 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 --mls16384 --bsr13 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	1000	--i1000
maximum blocks	8	--mb8
maximum length score	16384	--mls16384
block splitting recursion	13	--bsr13
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/1.0.1/underscore-min.js --location | md5sum
d4052e0252f869c7b55ed7bc0544a2e5 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.1.min.zopfli.js.gz | md5sum
d4052e0252f869c7b55ed7bc0544a2e5 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.0.1/underscore-min.js --location | sha1sum
710c3a99f0bd456c2fd6dcbcbd1e500e0646ec19 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.1.min.zopfli.js.gz | sha1sum
710c3a99f0bd456c2fd6dcbcbd1e500e0646ec19 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3253 bytes	d4052e0252f869c7b55ed7bc0544a2e5	(invalid)
cdnjs	2954 bytes	d4052e0252f869c7b55ed7bc0544a2e5	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2967 bytes	5356dab7f73f272b96ea0ced070b74ef	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
2864 bytes	-2 bytes	zopfli --i1000 --mls16384 --bsr13 --lazy --ohh	February 2, 2016 @ 19:45
2866 bytes	–	zopfli --i100 --mls1024 --bsr4 --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 @ 12:56.

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	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
4	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
6	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
7	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
8	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
9	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
10	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
11	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
12	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
13	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
14	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
15	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
16	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
17	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
18	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
19	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
20	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
21	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
22	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
23	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
25	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
30	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864
40	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864	2864

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	2866 bytes	–	100%
1,000	2864 bytes	-2 bytes	100%
10,000	2864 bytes	–	100%
100,000	2864 bytes	–	100%
1,000,000	2864 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)	2867 bytes	+3 bytes (+0.10%)	–
1	2867 bytes	+3 bytes (+0.10%)	–
2	2898 bytes	+34 bytes (+1.19%)	+31 bytes
3	2932 bytes	+68 bytes (+2.37%)	+65 bytes
4	2946 bytes	+82 bytes (+2.86%)	+79 bytes
5	2975 bytes	+111 bytes (+3.88%)	+108 bytes
6	3008 bytes	+144 bytes (+5.03%)	+141 bytes
7	3044 bytes	+180 bytes (+6.28%)	+177 bytes
8	3080 bytes	+216 bytes (+7.54%)	+213 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	2578 bytes	-286 bytes (-9.99%)
Brotli (Wikipedia)	brotli	brotli -q 11	2664 bytes	-200 bytes (-6.98%)
Zstandard (Wikipedia)	zstd	zstd -19	2882 bytes	+18 bytes (+0.63%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2904 bytes	+40 bytes (+1.40%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2917 bytes	+53 bytes (+1.85%)
LZMA2 (Wikipedia)	xz	xz -9	2956 bytes	+92 bytes (+3.21%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3458 bytes	+594 bytes (+20.74%)

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.