UnderscoreJS 0.3.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 15773 bytes (15.4k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 5711 bytes (5.6k, 36%).

After GZIP compression these minified files vary in size:

Boot	2138 bytes (2.1k)	CDN
gzip -6 (default)	1961 bytes (1.9k)	local copy
gzip -9	1961 bytes (1.9k)	local copy
Baidu	1945 bytes (1.9k)	CDN
cdnjs	1945 bytes (1.9k)	CDN
libdeflate -12	1901 bytes (1.9k)	local copy
7zip -mx=9 -tgzip	1898 bytes (1.9k)	local copy
kzip -s0 -rn -b1	1898 bytes (1.9k)	local copy
pigz -11 -n	1897 bytes (1.9k)	local copy
zultra	1896 bytes (1.9k)	local copy
Zopfli	1894 bytes (1.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.3.0 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 51 bytes by using my UnderscoreJS 0.3.0 Zopfli version instead of the best available CDN (2.69% smaller than cdnjs, 1894 vs. 1945 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 --i10000 --mb8 --mls8 --bsr21 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	8	--mls8
block splitting recursion	21	--bsr21
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/0.3.0/underscore-min.js --location | md5sum
c021a41da175481caf8a8bae31c6104b -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.0.min.zopfli.js.gz | md5sum
c021a41da175481caf8a8bae31c6104b -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.3.0/underscore-min.js --location | sha1sum
5f7e66c336f3a7974347b135524ba8863c64cbf8 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.3.0.min.zopfli.js.gz | sha1sum
5f7e66c336f3a7974347b135524ba8863c64cbf8 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2138 bytes	c021a41da175481caf8a8bae31c6104b	(invalid)
Baidu	1945 bytes	c021a41da175481caf8a8bae31c6104b	(invalid)
cdnjs	1945 bytes	c021a41da175481caf8a8bae31c6104b	(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
1894 bytes	-1 byte	zopfli --i10000 --mls8 --bsr21 --lazy --ohh	February 2, 2016 @ 23:17
1895 bytes	–	zopfli --i100 --mls16 --bsr7 --lazy --ohh	February 2, 2016 @ 20:57

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:
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	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
4	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
6	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
7	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
8	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
9	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
10	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
11	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
12	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
13	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
14	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
15	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
16	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
17	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
18	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
19	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
20	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
21	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
22	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
23	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
25	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
30	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895
40	1895	1895	1894	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895	1895

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	1895 bytes	–	100%
1,000	1895 bytes	–	100%
10,000	1894 bytes	-1 byte	100%
100,000	1894 bytes	–	6.67%
1,000,000	1894 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)	1898 bytes	+4 bytes (+0.21%)	–
1	1898 bytes	+4 bytes (+0.21%)	–
2	1917 bytes	+23 bytes (+1.21%)	+19 bytes
3	1942 bytes	+48 bytes (+2.53%)	+44 bytes
4	1977 bytes	+83 bytes (+4.38%)	+79 bytes
5	2001 bytes	+107 bytes (+5.65%)	+103 bytes
6	2035 bytes	+141 bytes (+7.44%)	+137 bytes
7	2055 bytes	+161 bytes (+8.50%)	+157 bytes
8	2086 bytes	+192 bytes (+10.14%)	+188 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
Brotli (Wikipedia)	brotli	brotli -q 11	1715 bytes	-179 bytes (-9.45%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	1735 bytes	-159 bytes (-8.39%)
Zstandard (Wikipedia)	zstd	zstd -19	1921 bytes	+27 bytes (+1.43%)
LZMA2 (Wikipedia)	xz	xz -9	1984 bytes	+90 bytes (+4.75%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	1992 bytes	+98 bytes (+5.17%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2039 bytes	+145 bytes (+7.66%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	2645 bytes	+751 bytes (+39.65%)

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.