Bootstrap 5.2.1 - as small as it gets (near-perfect GZIP compression)

Choose a version:

The original file has 145628 bytes (142.2k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 60441 bytes (59.0k, 42%).

After GZIP compression these minified files vary in size:

gzip -6 (default)	16176 bytes (15.8k)	local copy
jsdelivr	16154 bytes (15.8k)	CDN
cdnjs	16111 bytes (15.7k)	CDN
gzip -9	16111 bytes (15.7k)	local copy
libdeflate -12	15611 bytes (15.2k)	local copy
7zip -mx=9 -tgzip	15593 bytes (15.2k)	local copy
zultra	15553 bytes (15.2k)	local copy
pigz -11 -n	15539 bytes (15.2k)	local copy
kzip -s0 -rn -b2	15533 bytes (15.2k)	local copy
Zopfli	15527 bytes (15.2k)	local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.2.1.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 5.2.1 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 584 bytes by using my Bootstrap 5.2.1 Zopfli version instead of the best available CDN (3.76% smaller than cdnjs, 15527 vs. 16111 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 --i1000000 --mb8 --mls1024 --bsr14 --lazy --ohh

(found September 20, 2022)

Description	Value	Parameter
iterations	1000000	--i1000000
maximum blocks	8	--mb8
maximum length score	1024	--mls1024
block splitting recursion	14	--bsr14
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/twbs/bootstrap/v5.2.1/dist/js/bootstrap.min.js --location | md5sum
6a599114d93cc36d2c8e127a24a97e0a -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.2.1.min.zopfli.js.gz | md5sum
6a599114d93cc36d2c8e127a24a97e0a -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v5.2.1/dist/js/bootstrap.min.js --location | sha1sum
45be8ca0bae7e5b88244b718d4133c6aabd30cd8 -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.2.1.min.zopfli.js.gz | sha1sum
45be8ca0bae7e5b88244b718d4133c6aabd30cd8 -

All listed CDNs deliver identical contents:

CDN	Size (compressed)	MD5 (uncompressed)	Timestamp
jsdelivr	16154 bytes	6a599114d93cc36d2c8e127a24a97e0a	September 19, 2022 @ 14:38
cdnjs	16111 bytes	6a599114d93cc36d2c8e127a24a97e0a	(invalid)

Note: only the MD5 hashes are shown to keep things simple.

Other Versions

Available Bootstrap versions at minime.stephan-brumme.com:

5.2.3, 5.2.2, 5.2.1, 5.2.0,
5.1.3, 5.1.2, 5.1.1, 5.1.0,
5.0.2, 5.0.1, 5.0.0,
4.6.0,
4.5.3, 4.5.2, 4.5.1, 4.5.0,
4.4.1, 4.4.0,
4.3.1, 4.3.0,
4.2.1, 4.2.0,
4.1.3, 4.1.2, 4.1.1, 4.1.0, 4.0.0,
3.4.1, 3.4.0,
3.3.7, 3.3.6, 3.3.5, 3.3.4, 3.3.2, 3.3.1, 3.3.0,
3.2.0,
3.1.1, 3.1.0,
3.0.3, 3.0.2, 3.0.1, 3.0.0

The project site contains an overview how well these versions were compressed.
Other interesting projects are AngularJS, BackboneJS, D3, Dojo, Ember, jQuery, Knockout, lodash, React, Socket.IO, ThreeJS, UnderscoreJS and Vue.

Changelog

Best Zopfli parameters so far:

Size	Improvement	Parameters	Found
15527 bytes	-1 byte	zopfli --i1000000 --mls1024 --bsr14 --lazy --ohh	September 20, 2022 @ 17:48
15528 bytes	-1 byte	zopfli --i100000 --mls4096 --bsr14 --lazy --ohh	September 20, 2022 @ 11:24
15529 bytes	-1 byte	zopfli --i10000 --mls128 --bsr18 --lazy --ohh	September 19, 2022 @ 15:56
15530 bytes	-1 byte	zopfli --i10000 --mls256 --bsr40 --lazy --ohh	September 19, 2022 @ 15:56
15531 bytes	-1 byte	zopfli --i1000 --mls128 --bsr25 --lazy --ohh	September 19, 2022 @ 15:20
15532 bytes	-1 byte	zopfli --i1000 --mls1024 --bsr40 --lazy --ohh	September 19, 2022 @ 15:18
15533 bytes	-1 byte	zopfli --i1000 --mls4 --bsr14 --lazy --ohh	September 19, 2022 @ 15:18
15534 bytes	–	zopfli --i100 --mls4 --bsr14 --lazy --ohh	September 19, 2022 @ 14:58

If there are multiple parameter sets yielding the same compressed size, only the first one found is shown.

Most recent activity on September 21, 2022 @ 01:32.

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	15537	15536	15536	15536	15536	15535	15534	15536	15539	15537	15538	15538	15538	15540	15536
4	15536	15543	15535	15535	15542	15530	15530	15534	15534	15532	15532	15532	15538	15540	15533
6	15534	15534	15534	15537	15533	15539	15536	15536	15532	15534	15536	15531	15531	15534	15534
7	15534	15531	15536	15538	15536	15536	15534	15536	15537	15530	15531	15530	15530	15535	15531
8	15538	15538	15539	15538	15538	15539	15536	15537	15537	15530	15531	15531	15532	15540	15538
9	15533	15530	15535	15542	15539	15542	15535	15533	15537	15528	15531	15531	15538	15534	15532
10	15539	15530	15538	15538	15538	15531	15536	15536	15536	15530	15531	15531	15534	15533	15539
11	15538	15531	15539	15538	15537	15537	15529	15531	15540	15530	15533	15531	15538	15536	15531
12	15542	15543	15531	15542	15532	15534	15534	15536	15537	15533	15535	15535	15537	15533	15531
13	15539	15540	15539	15538	15538	15532	15535	15536	15532	15530	15535	15536	15532	15533	15531
14	15531	15531	15535	15541	15536	15535	15536	15532	15530	15527	15533	15527	15532	15538	15531
15	15530	15531	15538	15537	15536	15542	15536	15536	15536	15535	15534	15536	15532	15533	15540
16	15531	15530	15537	15538	15532	15531	15536	15531	15531	15531	15531	15531	15537	15534	15531
17	15534	15534	15536	15535	15533	15541	15536	15536	15530	15533	15531	15531	15531	15533	15539
18	15531	15531	15538	15537	15538	15533	15529	15536	15536	15536	15533	15536	15536	15534	15532
19	15535	15530	15535	15533	15536	15542	15536	15536	15536	15535	15531	15531	15532	15534	15531
20	15535	15539	15538	15538	15530	15537	15535	15536	15536	15533	15535	15535	15537	15534	15531
21	15532	15531	15531	15538	15538	15532	15536	15530	15538	15530	15531	15535	15531	15534	15539
22	15534	15535	15534	15534	15533	15542	15536	15536	15532	15532	15531	15531	15530	15534	15531
23	15531	15540	15531	15538	15538	15539	15529	15530	15536	15536	15536	15531	15532	15534	15531
25	15531	15539	15539	15534	15536	15532	15529	15536	15536	15532	15534	15535	15537	15533	15531
30	15533	15531	15539	15538	15532	15537	15536	15536	15531	15536	15531	15536	15537	15533	15544
40	15539	15540	15539	15538	15532	15533	15529	15530	15530	15529	15531	15535	15535	15534	15532

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	15534 bytes	–	100%
1,000	15531 bytes	-3 bytes	100%
10,000	15529 bytes	-2 bytes	100%
100,000	15528 bytes	-1 byte	2.61%
1,000,000	15527 bytes	-1 byte	0.87%
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)	15628 bytes	+101 bytes (+0.65%)	+95 bytes
1	15628 bytes	+101 bytes (+0.65%)	+95 bytes
2	15533 bytes	+6 bytes (+0.04%)	–
3	15563 bytes	+36 bytes (+0.23%)	+30 bytes
4	15579 bytes	+52 bytes (+0.33%)	+46 bytes
5	15604 bytes	+77 bytes (+0.50%)	+71 bytes
6	15643 bytes	+116 bytes (+0.75%)	+110 bytes
7	15642 bytes	+115 bytes (+0.74%)	+109 bytes
8	15686 bytes	+159 bytes (+1.02%)	+153 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	13125 bytes	-2402 bytes (-15.47%)
ZPAQ (Wikipedia)	zpaq	zpaq -method 69	13471 bytes	-2056 bytes (-13.24%)
Brotli (Wikipedia)	brotli	brotli -q 11	14435 bytes	-1092 bytes (-7.03%)
Burrows-Wheeler transform (Wikipedia)	bzip2	bzip2 -9	15224 bytes	-303 bytes (-1.95%)
LZMA2 (Wikipedia)	xz	xz -9	15288 bytes	-239 bytes (-1.54%)
Zstandard (Wikipedia)	zstd	zstd -19	15369 bytes	-158 bytes (-1.02%)
PPMd (Wikipedia)	7zip	7za a -mx=9 -m0=ppmd	15566 bytes	+39 bytes (+0.25%)

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.