Choose a version:
40% The original file has 148578 bytes (145.1k) and is available from the project website.
There you can find the official minified version, too, which brings down the size to 60089 bytes (58.7k, 40%).

After GZIP compression these minified files vary in size:
unpkg
  22313 bytes (21.8k)
CDN
gzip -6 (default)
  15959 bytes (15.6k)
local copy
jsdelivr
  15925 bytes (15.6k)
CDN
gzip -9
  15874 bytes (15.5k)
local copy
cdnjs
  15866 bytes (15.5k)
CDN
libdeflate -12
  15351 bytes (15.0k)
local copy
7zip -mx=9 -tgzip
  15341 bytes (15.0k)
local copy
zultra
  15307 bytes (14.9k)
local copy
kzip -s0 -rn -b2
  15293 bytes (14.9k)
local copy
pigz -11 -n
  15290 bytes (14.9k)
local copy
Zopfli
  15278 bytes (14.9k)
local copy

perma-link to the smallest file on my server:
http://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.0.2.min.js (or via HTTPS)

You will automatically get the smallest Bootstrap 5.0.2 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 588 bytes by using my Bootstrap 5.0.2 Zopfli version instead of the best available CDN (3.85% smaller than cdnjs, 15278 vs. 15866 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 --i1000000 --mb8 --mls32 --bsr25 --lazy --ohh

(found June 29, 2021)
Description Value Parameter
iterations 1000000  --i1000000
maximum blocks 8  --mb8
maximum length score 32  --mls32
block splitting recursion 25  --bsr25
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/v5.0.2/dist/js/bootstrap.min.js --location | md5sum
a08792f518b51f0f1422b5c96df9eb8a  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.0.2.min.zopfli.js.gz | md5sum
a08792f518b51f0f1422b5c96df9eb8a  -

SHA1:
curl --silent --compressed https://raw.githubusercontent.com/twbs/bootstrap/v5.0.2/dist/js/bootstrap.min.js --location | sha1sum
3f094f010bfb0c022a51b62778d4361d1cad3fd6  -
curl --silent --compressed https://minime.stephan-brumme.com/files/bootstrap/bootstrap-5.0.2.min.zopfli.js.gz | sha1sum
3f094f010bfb0c022a51b62778d4361d1cad3fd6  -

All listed CDNs deliver identical contents:
CDN Size (compressed) MD5 (uncompressed) Timestamp
unpkg 22313 bytes a08792f518b51f0f1422b5c96df9eb8a (invalid)
jsdelivr 15925 bytes a08792f518b51f0f1422b5c96df9eb8a June 29, 2021 @ 12:56
cdnjs 15866 bytes a08792f518b51f0f1422b5c96df9eb8a (invalid)

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

Other Versions

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

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
15278 bytes -1 byte zopfli --i1000000 --mls32 --bsr25 --lazy --ohh June 29, 2021 @ 20:08
15279 bytes -1 byte zopfli --i100000 --mls1024 --bsr16 --lazy --ohh June 29, 2021 @ 13:35
15280 bytes -1 byte zopfli --i10000 --mls1024 --bsr16 --lazy --ohh June 29, 2021 @ 13:06
15281 bytes -1 byte zopfli --i1000 --mls1024 --bsr16 --lazy --ohh June 29, 2021 @ 13:02
15282 bytes -2 bytes zopfli --i1000 --mls2048 --bsr23 --lazy --ohh June 29, 2021 @ 13:02
15284 bytes zopfli --i100 --mls32 --bsr6 --lazy --ohh June 29, 2021 @ 12:58

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

Most recent activity on June 30, 2021 @ 13:00.

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
15285 15285 15285 15285 15284 15284 15286 15288 15288 15289 15289 15291 15290 15288 15303
15285 15286 15286 15285 15287 15290 15289 15288 15290 15291 15282 15286 15284 15290 15288
15279 15279 15281 15281 15281 15288 15281 15283 15285 15281 15280 15285 15292 15279 15289
15285 15283 15286 15284 15284 15284 15284 15285 15286 15285 15283 15282 15284 15291 15282
15285 15286 15281 15285 15285 15284 15284 15284 15288 15285 15282 15282 15288 15285 15281
15285 15284 15279 15285 15285 15285 15284 15285 15285 15282 15284 15281 15289 15285 15292
15286 15281 15285 15281 15279 15284 15284 15284 15287 15284 15285 15282 15283 15292 15295
15286 15285 15281 15280 15285 15284 15285 15284 15285 15282 15282 15279 15285 15284 15292
15284 15284 15281 15285 15284 15284 15284 15284 15285 15282 15282 15281 15288 15285 15281
15279 15284 15281 15279 15285 15284 15284 15284 15286 15282 15283 15282 15288 15291 15292
15285 15285 15281 15284 15284 15284 15284 15284 15286 15286 15286 15282 15289 15291 15289
15286 15284 15286 15284 15284 15284 15284 15284 15285 15285 15281 15282 15289 15285 15290
15285 15282 15281 15279 15282 15281 15284 15284 15284 15279 15282 15285 15290 15290 15290
15282 15285 15282 15278 15285 15284 15283 15284 15286 15285 15282 15281 15292 15291 15290
15285 15284 15284 15284 15285 15284 15284 15284 15286 15284 15281 15281 15279 15281 15281
15279 15281 15286 15281 15284 15283 15281 15284 15285 15286 15279 15281 15288 15285 15281
15284 15284 15286 15284 15286 15284 15284 15283 15285 15285 15286 15282 15292 15285 15289
15284 15284 15281 15285 15284 15284 15284 15284 15285 15284 15281 15279 15288 15285 15292
15281 15279 15285 15280 15278 15291 15281 15281 15285 15285 15285 15281 15291 15291 15290
15285 15284 15281 15284 15284 15284 15284 15284 15285 15287 15281 15282 15282 15291 15282
15279 15281 15286 15279 15278 15283 15281 15283 15285 15285 15286 15282 15289 15291 15290
15279 15284 15281 15279 15279 15284 15284 15283 15285 15285 15281 15282 15290 15285 15290
15285 15282 15282 15282 15282 15285 15282 15284 15286 15284 15282 15282 15289 15290 15281

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 15284 bytes 100%
1,000 15281 bytes -3 bytes 100%
10,000 15280 bytes -1 byte 100%
100,000 15279 bytes -1 byte 7.54%
1,000,000 15278 bytes -1 byte 6.67%
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
15387 bytes +109 bytes (+0.71%) +94 bytes
15387 bytes +109 bytes (+0.71%) +94 bytes
15293 bytes +15 bytes (+0.10%)
15320 bytes +42 bytes (+0.27%) +27 bytes
15322 bytes +44 bytes (+0.29%) +29 bytes
15356 bytes +78 bytes (+0.51%) +63 bytes
15391 bytes +113 bytes (+0.74%) +98 bytes
15415 bytes +137 bytes (+0.90%) +122 bytes
15450 bytes +172 bytes (+1.13%) +157 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 12803 bytes -2475 bytes (-16.20%)
ZPAQ (Wikipedia) zpaq zpaq -method 69 13226 bytes -2052 bytes (-13.43%)
Brotli (Wikipedia) brotli brotli -q 11 14190 bytes -1088 bytes (-7.12%)
Burrows-Wheeler transform (Wikipedia) bzip2 bzip2 -9 14866 bytes -412 bytes (-2.70%)
LZMA2 (Wikipedia) xz xz -9 15044 bytes -234 bytes (-1.53%)
Zstandard (Wikipedia) zstd zstd -19 15157 bytes -121 bytes (-0.79%)
PPMd (Wikipedia) 7zip 7za a -mx=9 -m0=ppmd 15363 bytes +85 bytes (+0.56%)

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.