UnderscoreJS 0.4.7 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 20652 bytes (20.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 7595 bytes (7.4k, 37%).

After GZIP compression these minified files vary in size:

Boot	2702 bytes (2.6k)	CDN
gzip -6 (default)	2447 bytes (2.4k)	local copy
gzip -9	2445 bytes (2.4k)	local copy
Baidu	2441 bytes (2.4k)	CDN
cdnjs	2432 bytes (2.4k)	CDN
7zip -mx=9 -tgzip	2375 bytes (2.3k)	local copy
zultra	2375 bytes (2.3k)	local copy
libdeflate -12	2374 bytes (2.3k)	local copy
kzip -s0 -rn -b0	2372 bytes (2.3k)	local copy
pigz -11 -n	2372 bytes (2.3k)	local copy
Zopfli	2369 bytes (2.3k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.7.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.4.7 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 63 bytes by using my UnderscoreJS 0.4.7 Zopfli version instead of the best available CDN (2.66% smaller than cdnjs, 2369 vs. 2432 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 --mls32768 --bsr10 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	1000	--i1000
maximum blocks	8	--mb8
maximum length score	32768	--mls32768
block splitting recursion	10	--bsr10
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/0.4.7/underscore-min.js --location | md5sum
24ef658fdf19c9b776d88433b826ca2e -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.7.min.zopfli.js.gz | md5sum
24ef658fdf19c9b776d88433b826ca2e -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.4.7/underscore-min.js --location | sha1sum
eb4815b3ecf807789c85bf826b20a42fc160b6d0 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.4.7.min.zopfli.js.gz | sha1sum
eb4815b3ecf807789c85bf826b20a42fc160b6d0 -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2702 bytes	24ef658fdf19c9b776d88433b826ca2e	(invalid)
cdnjs	2432 bytes	24ef658fdf19c9b776d88433b826ca2e	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2441 bytes	7108b98977bda92b7edc6ffb5160dc18	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
2369 bytes	-2 bytes	zopfli --i1000 --mls32768 --bsr10 --lazy --ohh	February 2, 2016 @ 20:58
2371 bytes	–	zopfli --i100 --mls32768 --bsr10 --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 @ 12:43.

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	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
4	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
6	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
7	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
8	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
9	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
10	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
11	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
12	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
13	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
14	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
15	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
16	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
17	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
18	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
19	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
20	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
21	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
22	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
23	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
25	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
30	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369
40	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369	2369

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	2370 bytes	–	100%
1,000	2369 bytes	-1 byte	100%
10,000	2369 bytes	–	100%
100,000	2369 bytes	–	100%
1,000,000	2369 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)	2372 bytes	+3 bytes (+0.13%)	–
1	2373 bytes	+4 bytes (+0.17%)	+1 byte
2	2400 bytes	+31 bytes (+1.31%)	+28 bytes
3	2424 bytes	+55 bytes (+2.32%)	+52 bytes
4	2458 bytes	+89 bytes (+3.76%)	+86 bytes
5	2481 bytes	+112 bytes (+4.73%)	+109 bytes
6	2512 bytes	+143 bytes (+6.04%)	+140 bytes
7	2547 bytes	+178 bytes (+7.51%)	+175 bytes
8	2578 bytes	+209 bytes (+8.82%)	+206 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	2140 bytes	-229 bytes (-9.67%)
Brotli (Wikipedia)	brotli	brotli -q 11	2185 bytes	-184 bytes (-7.77%)
Zstandard (Wikipedia)	zstd	zstd -19	2387 bytes	+18 bytes (+0.76%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2453 bytes	+84 bytes (+3.55%)
LZMA2 (Wikipedia)	xz	xz -9	2468 bytes	+99 bytes (+4.18%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2621 bytes	+252 bytes (+10.64%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3046 bytes	+677 bytes (+28.58%)

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.