UnderscoreJS 0.6.0 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 24583 bytes (24.0k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 8533 bytes (8.3k, 35%).

After GZIP compression these minified files vary in size:

Boot	3228 bytes (3.2k)	CDN
gzip -6 (default)	2940 bytes (2.9k)	local copy
gzip -9	2935 bytes (2.9k)	local copy
Baidu	2931 bytes (2.9k)	CDN
cdnjs	2921 bytes (2.9k)	CDN
libdeflate -12	2842 bytes (2.8k)	local copy
7zip -mx=9 -tgzip	2841 bytes (2.8k)	local copy
zultra	2841 bytes (2.8k)	local copy
kzip -s0 -rn -b1	2839 bytes (2.8k)	local copy
pigz -11 -n	2839 bytes (2.8k)	local copy
Zopfli	2838 bytes (2.8k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.6.0.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.6.0 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 83 bytes by using my UnderscoreJS 0.6.0 Zopfli version instead of the best available CDN (2.92% smaller than cdnjs, 2838 vs. 2921 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 --mls16384 --bsr40 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	100	--i100
maximum blocks	8	--mb8
maximum length score	16384	--mls16384
block splitting recursion	40	--bsr40
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/0.6.0/underscore-min.js --location | md5sum
d30fd2cb756dba39b833a8bcbb58ad79 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.6.0.min.zopfli.js.gz | md5sum
d30fd2cb756dba39b833a8bcbb58ad79 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.6.0/underscore-min.js --location | sha1sum
1b0b2163a1b8f8e7435942768e6fa545a331b70f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.6.0.min.zopfli.js.gz | sha1sum
1b0b2163a1b8f8e7435942768e6fa545a331b70f -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	3228 bytes	d30fd2cb756dba39b833a8bcbb58ad79	(invalid)
cdnjs	2921 bytes	d30fd2cb756dba39b833a8bcbb58ad79	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2931 bytes	96acd6c1e31b55e606aaf87c58a6a87f	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
2838 bytes	–	zopfli --i100 --mls16384 --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 @ 12:52.

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	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
4	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
6	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
7	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
8	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
9	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
10	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
11	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
12	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
13	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
14	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
15	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
16	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
17	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
18	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
19	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
20	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
21	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
22	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
23	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
25	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
30	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838
40	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838	2838

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	2838 bytes	–	100%
1,000	2838 bytes	–	100%
10,000	2838 bytes	–	100%
100,000	2838 bytes	–	100%
1,000,000	2838 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)	2839 bytes	+1 byte (+0.04%)	–
1	2839 bytes	+1 byte (+0.04%)	–
2	2870 bytes	+32 bytes (+1.13%)	+31 bytes
3	2906 bytes	+68 bytes (+2.40%)	+67 bytes
4	2920 bytes	+82 bytes (+2.89%)	+81 bytes
5	2949 bytes	+111 bytes (+3.91%)	+110 bytes
6	2982 bytes	+144 bytes (+5.07%)	+143 bytes
7	3016 bytes	+178 bytes (+6.27%)	+177 bytes
8	3049 bytes	+211 bytes (+7.43%)	+210 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	2555 bytes	-283 bytes (-9.97%)
Brotli (Wikipedia)	brotli	brotli -q 11	2640 bytes	-198 bytes (-6.98%)
Zstandard (Wikipedia)	zstd	zstd -19	2854 bytes	+16 bytes (+0.56%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2875 bytes	+37 bytes (+1.30%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2897 bytes	+59 bytes (+2.08%)
LZMA2 (Wikipedia)	xz	xz -9	2928 bytes	+90 bytes (+3.17%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3435 bytes	+597 bytes (+21.04%)

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.