UnderscoreJS 1.0.3 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 24635 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 8542 bytes (8.3k, 35%).

After GZIP compression these minified files vary in size:

Boot	3226 bytes (3.2k)	CDN
gzip -6 (default)	2940 bytes (2.9k)	local copy
Baidu	2933 bytes (2.9k)	CDN
gzip -9	2932 bytes (2.9k)	local copy
unpkg	2920 bytes (2.9k)	CDN
cdnjs	2919 bytes (2.9k)	CDN
libdeflate -12	2840 bytes (2.8k)	local copy
zultra	2840 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2838 bytes (2.8k)	local copy
kzip -s0 -rn -b1	2838 bytes (2.8k)	local copy
pigz -11 -n	2836 bytes (2.8k)	local copy
Zopfli	2835 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.3.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.0.3 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 84 bytes by using my UnderscoreJS 1.0.3 Zopfli version instead of the best available CDN (2.96% smaller than cdnjs, 2835 vs. 2919 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 --i100 --mb8 --mls16 --bsr21 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	100	--i100
maximum blocks	8	--mb8
maximum length score	16	--mls16
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/1.0.3/underscore-min.js --location | md5sum
212c425ad364a0d4e9f195c2ee88d12a -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.3.min.zopfli.js.gz | md5sum
212c425ad364a0d4e9f195c2ee88d12a -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.0.3/underscore-min.js --location | sha1sum
97f93241957893ebd7febc5b5bac9a7bd1d94a0f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.0.3.min.zopfli.js.gz | sha1sum
97f93241957893ebd7febc5b5bac9a7bd1d94a0f -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3226 bytes	212c425ad364a0d4e9f195c2ee88d12a	(invalid)
unpkg	2920 bytes	212c425ad364a0d4e9f195c2ee88d12a	July 11, 2016 @ 16:50
cdnjs	2919 bytes	212c425ad364a0d4e9f195c2ee88d12a	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2933 bytes	53c66bf4859af74420042c2dc6873b3a	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
2835 bytes	–	zopfli --i100 --mls16 --bsr21 --lazy --ohh	February 2, 2016 @ 19:07

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 @ 12:51.

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	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
4	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
6	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
7	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
8	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
9	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
10	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
11	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
12	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
13	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
14	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
15	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
16	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
17	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
18	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
19	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
20	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
21	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
22	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
23	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
25	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
30	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835
40	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835	2835

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	2835 bytes	–	100%
1,000	2835 bytes	–	100%
10,000	2835 bytes	–	100%
100,000	2835 bytes	–	100%
1,000,000	2835 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)	2838 bytes	+3 bytes (+0.11%)	–
1	2838 bytes	+3 bytes (+0.11%)	–
2	2862 bytes	+27 bytes (+0.95%)	+24 bytes
3	2895 bytes	+60 bytes (+2.12%)	+57 bytes
4	2905 bytes	+70 bytes (+2.47%)	+67 bytes
5	2935 bytes	+100 bytes (+3.53%)	+97 bytes
6	2966 bytes	+131 bytes (+4.62%)	+128 bytes
7	3005 bytes	+170 bytes (+6.00%)	+167 bytes
8	3040 bytes	+205 bytes (+7.23%)	+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
RAR (proprietary)	RAR	rar a -m5 -md64m -mc63:128t -mt1	2552 bytes	-283 bytes (-9.98%)
Brotli (Wikipedia)	brotli	brotli -q 11	2633 bytes	-202 bytes (-7.13%)
Zstandard (Wikipedia)	zstd	zstd -19	2853 bytes	+18 bytes (+0.63%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2859 bytes	+24 bytes (+0.85%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2891 bytes	+56 bytes (+1.98%)
LZMA2 (Wikipedia)	xz	xz -9	2924 bytes	+89 bytes (+3.14%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3428 bytes	+593 bytes (+20.92%)

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.