UnderscoreJS 1.8.3 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 52919 bytes (51.7k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 16449 bytes (16.1k, 31%).

After GZIP compression these minified files vary in size:

Boot	6574 bytes (6.4k)	CDN
jsdelivr	6574 bytes (6.4k)	CDN
gzip -6 (default)	5869 bytes (5.7k)	local copy
cdnjs	5862 bytes (5.7k)	CDN
gzip -9	5856 bytes (5.7k)	local copy
fastcdn	5843 bytes (5.7k)	CDN
unpkg	5843 bytes (5.7k)	CDN
Yandex	5835 bytes (5.7k)	CDN
libdeflate -12	5684 bytes (5.6k)	local copy
7zip -mx=9 -tgzip	5679 bytes (5.5k)	local copy
pigz -11 -n	5673 bytes (5.5k)	local copy
kzip -s0 -rn -b1	5672 bytes (5.5k)	local copy
zultra	5671 bytes (5.5k)	local copy
Zopfli	5664 bytes (5.5k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/underscorejs/underscore-1.8.3.min.js (or via HTTPS)

You will automatically get the smallest UnderscoreJS 1.8.3 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 171 bytes by using my UnderscoreJS 1.8.3 Zopfli version instead of the best available CDN (3.02% smaller than Yandex, 5664 vs. 5835 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 --i10000000 --mb8 --mls256 --bsr17 --lazy --ohh

(found November 11, 2015)

Description	Value	Parameter
iterations	10000000	--i10000000
maximum blocks	8	--mb8
maximum length score	256	--mls256
block splitting recursion	17	--bsr17
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/1.8.3/underscore-min.js --location | md5sum
543feb1ecaf06ea516f8cec5f9f3f279 -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.8.3.min.zopfli.js.gz | md5sum
543feb1ecaf06ea516f8cec5f9f3f279 -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/jashkenas/underscore/1.8.3/underscore-min.js --location | sha1sum
2a515632e0fd8ffdeb8d94cb25e44cf287feb32f -
curl --silent --compressed https://minime.stephan-brumme.com/files/underscorejs/underscore-1.8.3.min.zopfli.js.gz | sha1sum
2a515632e0fd8ffdeb8d94cb25e44cf287feb32f -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
Boot	6574 bytes	543feb1ecaf06ea516f8cec5f9f3f279	(invalid)
jsdelivr	6574 bytes	543feb1ecaf06ea516f8cec5f9f3f279	(invalid)
cdnjs	5862 bytes	543feb1ecaf06ea516f8cec5f9f3f279	(invalid)
fastcdn	5843 bytes	543feb1ecaf06ea516f8cec5f9f3f279	November 5, 2015 @ 05:55
unpkg	5843 bytes	543feb1ecaf06ea516f8cec5f9f3f279	July 11, 2016 @ 16:48
Yandex	5835 bytes	543feb1ecaf06ea516f8cec5f9f3f279	December 22, 2015 @ 17:09

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
5664 bytes	-1 byte	zopfli --i10000000 --mls256 --bsr17 --lazy --ohh	November 11, 2015 @ 21:13
5665 bytes	-2 bytes	zopfli --i100000 --mls256 --bsr17 --lazy --ohh	September 22, 2015 @ 20:02
5667 bytes	-1 byte	zopfli --i10000 --mls4096 --bsr12 --lazy --ohh	September 8, 2015 @ 11:05
5668 bytes	-1 byte	zopfli --i1000 --mls4096 --bsr6 --lazy --ohh	September 8, 2015 @ 10:37
5669 bytes	–	zopfli --i100 --mls8192 --bsr10 --lazy --ohh	September 8, 2015 @ 10:32

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 @ 12:50.

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, 1,000,000 or 10,000,000.

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	5671	5670	5680	5670	5670	5670	5670	5671	5670	5670	5670	5670	5669	5669	5669
4	5670	5670	5675	5670	5670	5675	5668	5670	5669	5670	5670	5668	5669	5668	5668
6	5680	5676	5671	5670	5677	5677	5671	5671	5669	5670	5670	5667	5667	5667	5667
7	5676	5674	5675	5670	5677	5674	5671	5672	5669	5670	5670	5667	5674	5672	5672
8	5673	5670	5675	5670	5677	5675	5671	5672	5669	5670	5670	5670	5669	5667	5667
9	5680	5675	5679	5670	5677	5670	5670	5672	5669	5670	5670	5670	5667	5667	5667
10	5680	5675	5675	5670	5677	5676	5678	5677	5669	5670	5670	5670	5667	5667	5667
11	5670	5670	5675	5670	5670	5670	5670	5672	5668	5670	5670	5670	5672	5671	5671
12	5673	5674	5677	5670	5677	5674	5671	5671	5669	5670	5670	5667	5669	5670	5670
13	5680	5674	5675	5670	5676	5670	5671	5670	5670	5670	5670	5670	5667	5667	5667
14	5672	5672	5674	5671	5670	5670	5671	5671	5669	5670	5670	5667	5668	5668	5668
15	5673	5677	5674	5670	5676	5675	5671	5679	5669	5670	5670	5667	5674	5667	5667
16	5680	5674	5675	5670	5676	5674	5670	5668	5669	5670	5670	5670	5667	5667	5667
17	5675	5674	5675	5670	5676	5675	5671	5664	5669	5670	5670	5670	5670	5667	5667
18	5674	5674	5675	5670	5677	5675	5670	5669	5669	5670	5670	5670	5667	5667	5667
19	5680	5680	5679	5670	5677	5675	5671	5677	5669	5670	5670	5670	5670	5667	5667
20	5674	5674	5679	5670	5677	5675	5671	5673	5669	5670	5670	5667	5669	5667	5667
21	5675	5676	5675	5670	5677	5675	5670	5677	5668	5670	5670	5670	5670	5667	5667
22	5672	5672	5679	5670	5678	5675	5671	5674	5669	5670	5670	5670	5667	5667	5667
23	5680	5674	5675	5670	5677	5675	5670	5669	5669	5670	5670	5670	5670	5667	5667
25	5674	5674	5675	5670	5677	5675	5671	5674	5669	5670	5670	5669	5667	5668	5668
30	5679	5675	5675	5670	5676	5675	5672	5672	5670	5670	5670	5667	5668	5668	5668
40	5679	5674	5675	5670	5676	5677	5672	5672	5670	5670	5670	5667	5668	5667	5667

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	5669 bytes	–	100%
1,000	5667 bytes	-2 bytes	100%
10,000	5667 bytes	–	100%
100,000	5665 bytes	-2 bytes	69.28%
1,000,000	5665 bytes	–	2.03%
10,000,000	5664 bytes	-1 byte	0.29%

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)	5672 bytes	+8 bytes (+0.14%)	–
1	5672 bytes	+8 bytes (+0.14%)	–
2	5696 bytes	+32 bytes (+0.56%)	+24 bytes
3	5727 bytes	+63 bytes (+1.11%)	+55 bytes
4	5746 bytes	+82 bytes (+1.45%)	+74 bytes
5	5755 bytes	+91 bytes (+1.61%)	+83 bytes
6	5789 bytes	+125 bytes (+2.21%)	+117 bytes
7	5829 bytes	+165 bytes (+2.91%)	+157 bytes
8	5856 bytes	+192 bytes (+3.39%)	+184 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	4996 bytes	-668 bytes (-11.79%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	5207 bytes	-457 bytes (-8.07%)
Brotli (Wikipedia)	brotli	brotli -q 11	5302 bytes	-362 bytes (-6.39%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	5576 bytes	-88 bytes (-1.55%)
Zstandard (Wikipedia)	zstd	zstd -19	5676 bytes	+12 bytes (+0.21%)
LZMA2 (Wikipedia)	xz	xz -9	5724 bytes	+60 bytes (+1.06%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	5782 bytes	+118 bytes (+2.08%)

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.