UnderscoreJS 0.5.4 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 22299 bytes (21.8k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 8194 bytes (8.0k, 37%).

After GZIP compression these minified files vary in size:

Boot	2960 bytes (2.9k)	CDN
gzip -6 (default)	2682 bytes (2.6k)	local copy
gzip -9	2681 bytes (2.6k)	local copy
Baidu	2678 bytes (2.6k)	CDN
cdnjs	2666 bytes (2.6k)	CDN
libdeflate -12	2605 bytes (2.5k)	local copy
zultra	2604 bytes (2.5k)	local copy
7zip -mx=9 -tgzip	2602 bytes (2.5k)	local copy
kzip -s0 -rn -b1	2599 bytes (2.5k)	local copy
pigz -11 -n	2599 bytes (2.5k)	local copy
Zopfli	2595 bytes (2.5k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-0.5.4.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 0.5.4 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 71 bytes by using my UnderscoreJS 0.5.4 Zopfli version instead of the best available CDN (2.74% smaller than cdnjs, 2595 vs. 2666 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 --bsr7 --lazy --ohh

(found February 2, 2016)

Description	Value	Parameter
iterations	10000	--i10000
maximum blocks	8	--mb8
maximum length score	8	--mls8
block splitting recursion	7	--bsr7
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/0.5.4/underscore-min.js --location | md5sum
426f6be73c1adb6234fa85520b8c4cf6 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.5.4.min.zopfli.js.gz | md5sum
426f6be73c1adb6234fa85520b8c4cf6 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/0.5.4/underscore-min.js --location | sha1sum
7ab2ea271ad5bd3de9e0f17ded546a25fc6d25fc -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-0.5.4.min.zopfli.js.gz | sha1sum
7ab2ea271ad5bd3de9e0f17ded546a25fc6d25fc -

These CDNs send you the original file:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	2960 bytes	426f6be73c1adb6234fa85520b8c4cf6	(invalid)
cdnjs	2666 bytes	426f6be73c1adb6234fa85520b8c4cf6	(invalid)

And some CDNs send you a different file:

CDN	Size (compressed)	MD5 (uncompressed)	Comment / Diff	Timestamp
Baidu	2678 bytes	dc17bde7ba8728cb1319be153930eb60	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
2595 bytes	-1 byte	zopfli --i10000 --mls8 --bsr7 --lazy --ohh	February 2, 2016 @ 23:28
2596 bytes	-1 byte	zopfli --i1000 --mls4096 --bsr20 --lazy --ohh	February 2, 2016 @ 20:59
2597 bytes	–	zopfli --i100 --mls16384 --bsr8 --lazy --ohh	February 2, 2016 @ 20:58

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:
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	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
4	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
6	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
7	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
8	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
9	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
10	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
11	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
12	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
13	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
14	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
15	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
16	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
17	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
18	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
19	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
20	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
21	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
22	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
23	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
25	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
30	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595
40	2595	2595	2595	2595	2595	2595	2595	2596	2595	2595	2596	2595	2595	2595	2595

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	2597 bytes	–	100%
1,000	2596 bytes	-1 byte	100%
10,000	2595 bytes	-1 byte	100%
100,000	2595 bytes	–	86.67%
1,000,000	2595 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)	2599 bytes	+4 bytes (+0.15%)	–
1	2599 bytes	+4 bytes (+0.15%)	–
2	2622 bytes	+27 bytes (+1.04%)	+23 bytes
3	2656 bytes	+61 bytes (+2.35%)	+57 bytes
4	2669 bytes	+74 bytes (+2.85%)	+70 bytes
5	2696 bytes	+101 bytes (+3.89%)	+97 bytes
6	2723 bytes	+128 bytes (+4.93%)	+124 bytes
7	2758 bytes	+163 bytes (+6.28%)	+159 bytes
8	2793 bytes	+198 bytes (+7.63%)	+194 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	2325 bytes	-270 bytes (-10.40%)
Brotli (Wikipedia)	brotli	brotli -q 11	2399 bytes	-196 bytes (-7.55%)
Zstandard (Wikipedia)	zstd	zstd -19	2609 bytes	+14 bytes (+0.54%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	2646 bytes	+51 bytes (+1.97%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	2677 bytes	+82 bytes (+3.16%)
LZMA2 (Wikipedia)	xz	xz -9	2696 bytes	+101 bytes (+3.89%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	3221 bytes	+626 bytes (+24.12%)

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.