Choose a version:
41% The original file has 150397 bytes (146.9k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 61015 bytes (59.6k, 41%).

After GZIP compression these minified files vary in size:
gzip -6 (default)
  15984 bytes (15.6k)
local copy
jsdelivr
  15953 bytes (15.6k)
CDN
gzip -9
  15913 bytes (15.5k)
local copy
cdnjs
  15897 bytes (15.5k)
CDN
libdeflate -12
  15420 bytes (15.1k)
local copy
7zip -mx=9 -tgzip
  15380 bytes (15.0k)
local copy
zultra
  15340 bytes (15.0k)
local copy
pigz -11 -n
  15324 bytes (15.0k)
local copy
kzip -s0 -rn -b2
  15320 bytes (15.0k)
local copy
Zopfli
  15312 bytes (15.0k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.0.0.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 5.0.0 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 585 bytes by using my Bootstrap 5.0.0 Zopfli version instead of the best available CDN (3.82% smaller than cdnjs, 15312 vs. 15897 bytes):
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 --i100000 --mb8 --mls4 --bsr11 --lazy --ohh

(found June 9, 2021)
Description Value Parameter
iterations 100000  --i100000
maximum blocks 8  --mb8
maximum length score 4  --mls4
block splitting recursion 11  --bsr11
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/v5.0.0/dist/js/bootstrap.min.js --location | md5sum
2abd6b85cc1199365cb08e558d359c40  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.0.0.min.zopfli.js.gz | md5sum
2abd6b85cc1199365cb08e558d359c40  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v5.0.0/dist/js/bootstrap.min.js --location | sha1sum
14f86bc86432e4aff6360a75fedff7ea1fd2a3e1  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.0.0.min.zopfli.js.gz | sha1sum
14f86bc86432e4aff6360a75fedff7ea1fd2a3e1  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
jsdelivr 15953 bytes 2abd6b85cc1199365cb08e558d359c40 June 8, 2021 @ 10:05
cdnjs 15897 bytes 2abd6b85cc1199365cb08e558d359c40 (invalid)

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

Other Versions

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

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
15312 bytes -1 byte zopfli --i100000 --mls4 --bsr11 --lazy --ohh June 9, 2021 @ 12:27
15313 bytes -1 byte zopfli --i10000 --mls4 --bsr11 --lazy --ohh June 8, 2021 @ 12:23
15314 bytes -4 bytes zopfli --i10000 --mls16 --bsr11 --lazy --ohh June 8, 2021 @ 12:00
15318 bytes zopfli --i100 --mls8 --bsr30 --lazy --ohh June 8, 2021 @ 10:10

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

Most recent activity on June 9, 2021 @ 19:43.

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:
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
15323 15322 15323 15324 15322 15322 15321 15321 15319 15319 15322 15320 15320 15321 15321
15317 15319 15318 15317 15317 15320 15320 15318 15323 15317 15318 15319 15318 15318 15313
15321 15319 15317 15317 15317 15318 15318 15317 15319 15319 15319 15320 15321 15320 15317
15318 15312 15318 15319 15316 15317 15318 15318 15318 15318 15319 15317 15318 15318 15320
15319 15317 15318 15319 15317 15318 15317 15318 15319 15318 15317 15320 15320 15318 15317
15318 15318 15321 15317 15315 15316 15321 15318 15321 15319 15317 15317 15318 15320 15317
15319 15318 15318 15318 15318 15317 15317 15319 15317 15319 15318 15318 15319 15318 15317
15321 15312 15313 15313 15317 15317 15321 15318 15321 15318 15317 15320 15320 15315 15317
15320 15318 15318 15317 15317 15317 15318 15318 15318 15319 15319 15318 15317 15318 15317
15319 15319 15318 15317 15318 15318 15318 15318 15318 15319 15317 15318 15319 15318 15317
15319 15319 15322 15321 15320 15317 15319 15318 15318 15319 15320 15317 15319 15318 15317
15318 15318 15318 15317 15315 15317 15317 15318 15318 15318 15319 15317 15318 15318 15317
15319 15319 15319 15319 15317 15318 15318 15317 15318 15318 15320 15318 15317 15318 15313
15318 15319 15318 15318 15318 15318 15317 15318 15320 15318 15318 15319 15318 15320 15317
15320 15319 15317 15317 15315 15318 15318 15318 15321 15318 15317 15317 15318 15318 15317
15319 15318 15319 15321 15317 15319 15318 15318 15318 15318 15317 15317 15319 15318 15317
15320 15319 15318 15317 15317 15317 15317 15318 15319 15318 15317 15318 15318 15318 15317
15319 15319 15318 15317 15320 15317 15318 15318 15318 15319 15319 15319 15319 15318 15317
15321 15319 15318 15319 15317 15317 15317 15318 15320 15318 15318 15319 15317 15318 15317
15319 15318 15318 15317 15317 15317 15318 15318 15318 15319 15318 15319 15318 15320 15317
15320 15318 15318 15318 15317 15317 15318 15318 15321 15319 15317 15318 15319 15320 15317
15318 15318 15318 15317 15318 15317 15317 15318 15318 15319 15318 15319 15318 15320 15317
15318 15319 15317 15318 15320 15318 15317 15318 15318 15318 15319 15320 15319 15318 15317

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 15318 bytes 100%
1,000 15318 bytes 100%
10,000 15313 bytes -5 bytes 100%
100,000 15312 bytes -1 byte 1.74%
1,000,000 15312 bytes 0.58%
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
15411 bytes +99 bytes (+0.65%) +91 bytes
15414 bytes +102 bytes (+0.67%) +94 bytes
15320 bytes +8 bytes (+0.05%)
15348 bytes +36 bytes (+0.24%) +28 bytes
15352 bytes +40 bytes (+0.26%) +32 bytes
15379 bytes +67 bytes (+0.44%) +59 bytes
15415 bytes +103 bytes (+0.67%) +95 bytes
15444 bytes +132 bytes (+0.86%) +124 bytes
15463 bytes +151 bytes (+0.99%) +143 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 12780 bytes -2532 bytes (-16.54%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 13120 bytes -2192 bytes (-14.32%)
Brotli (Wikipedia) brotli brotli -q 11 14198 bytes -1114 bytes (-7.28%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 14794 bytes -518 bytes (-3.38%)
LZMA2 (Wikipedia) xz xz -9 15048 bytes -264 bytes (-1.72%)
Zstandard (Wikipedia) zstd zstd -19 15154 bytes -158 bytes (-1.03%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 15396 bytes +84 bytes (+0.55%)

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):


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 2021.
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.