UnderscoreJS 0.1.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 14186 bytes (13.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 5166 bytes (5.0k, 36%).

After GZIP compression these minified files vary in size:

Boot	1959 bytes (1.9k)	CDN
gzip -6 (default)	1819 bytes (1.8k)	local copy
gzip -9	1815 bytes (1.8k)	local copy
Baidu	1802 bytes (1.8k)	CDN
cdnjs	1802 bytes (1.8k)	CDN
libdeflate -12	1758 bytes (1.7k)	local copy
pigz -11 -n	1757 bytes (1.7k)	local copy
zultra	1757 bytes (1.7k)	local copy
7zip -mx=9 -tgzip	1756 bytes (1.7k)	local copy
kzip -s0 -rn -b1	1755 bytes (1.7k)	local copy
Zopfli	1753 bytes (1.7k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.1.1.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.1.1 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 49 bytes by using my UnderscoreJS 0.1.1 Zopfli version instead of the best available CDN (2.80% smaller than cdnjs, 1753 vs. 1802 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 --mls32 --bsr6 --lazy --ohh

(found February 3, 2016)

Description	Value	Parameter
iterations	100000	--i100000
maximum blocks	8	--mb8
maximum length score	32	--mls32
block splitting recursion	6	--bsr6
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/0.1.1/underscore-min.js --location | md5sum
aca66999b9aac38815facffeb2f861da -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.1.1.min.zopfli.js.gz | md5sum
aca66999b9aac38815facffeb2f861da -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.1.1/underscore-min.js --location | sha1sum
e843c570455a2f6c308f433647ec9a739ac40e0a -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.1.1.min.zopfli.js.gz | sha1sum
e843c570455a2f6c308f433647ec9a739ac40e0a -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	1959 bytes	aca66999b9aac38815facffeb2f861da	(invalid)
Baidu	1802 bytes	aca66999b9aac38815facffeb2f861da	(invalid)
cdnjs	1802 bytes	aca66999b9aac38815facffeb2f861da	(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
1753 bytes	-1 byte	zopfli --i100000 --mls32 --bsr6 --lazy --ohh	February 3, 2016 @ 07:13
1754 bytes	-1 byte	zopfli --i10000 --mls32 --bsr6 --lazy --ohh	February 2, 2016 @ 23:18
1755 bytes	-1 byte	zopfli --i1000 --mls1024 --bsr40 --lazy --ohh	February 2, 2016 @ 20:57
1756 bytes	–	zopfli --i100 --mls1024 --bsr40 --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	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
4	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
6	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
7	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
8	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
9	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
10	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
11	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
12	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
13	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
14	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
15	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
16	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
17	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
18	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
19	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
20	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
21	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
22	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
23	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
25	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
30	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754
40	1755	1755	1753	1754	1753	1755	1753	1755	1754	1755	1755	1754	1754	1754	1754

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	1756 bytes	–	100%
1,000	1755 bytes	-1 byte	100%
10,000	1754 bytes	-1 byte	100%
100,000	1753 bytes	-1 byte	60.00%
1,000,000	1753 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)	1755 bytes	+2 bytes (+0.11%)	–
1	1755 bytes	+2 bytes (+0.11%)	–
2	1777 bytes	+24 bytes (+1.37%)	+22 bytes
3	1815 bytes	+62 bytes (+3.54%)	+60 bytes
4	1835 bytes	+82 bytes (+4.68%)	+80 bytes
5	1873 bytes	+120 bytes (+6.85%)	+118 bytes
6	1891 bytes	+138 bytes (+7.87%)	+136 bytes
7	1923 bytes	+170 bytes (+9.70%)	+168 bytes
8	1957 bytes	+204 bytes (+11.64%)	+202 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	1590 bytes	-163 bytes (-9.30%)
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	1631 bytes	-122 bytes (-6.96%)
Zstandard (Wikipedia)	zstd	zstd -19	1771 bytes	+18 bytes (+1.03%)
LZMA2 (Wikipedia)	xz	xz -9	1836 bytes	+83 bytes (+4.73%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	1857 bytes	+104 bytes (+5.93%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	1910 bytes	+157 bytes (+8.96%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	2532 bytes	+779 bytes (+44.44%)

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.