Bootstrap versions used in Joomla

Since Joomla 3.0.0

Bootstrap 5.3.3 used in Joomla 5.2.0-Beta3
Bootstrap 5.3.2 used in Joomla 4.4.0-Beta3 to 6.0.x
Bootstrap 5.3.1 used in Joomla 4.4.0-Alpha4 to 5.0.0-Beta2
Bootstrap 5.3.0 used in Joomla 4.4.0-Alpha3-dev to 5.0.0-Alpha3-Dev
Bootstrap 5.2.3 used in Joomla 4.3.0-Alpha3 to 4.3.0 / 4.4.0-Alpha1 / 5.0.0-Alpha3-dev
Bootstrap 5.1.3 used in Joomla 4.0.6-RC to 4.3.0-Alpha2
Bootstrap 5.1.2 used in Joomla 4.0.4-RC to 4.0.5
Bootstrap 5.0.2 used in Joomla 4.0.0-RC3 to 4.1.0-Alpha1
Bootstrap 5.0.1 used in Joomla 4.0.0-Beta8-dev to 4.0.0-RC2
Bootstrap 5.0.0 used in Joomla 4.0.0-Beta8-dev
Bootstrap 5.0.0-beta3 used in Joomla 4.0.0-Beta8-dev
Bootstrap 5.0.0-beta2 used in Joomla 4.0.0-Beta8-dev
Bootstrap 5.0.0-beta1 used in Joomla 4.0.0-Beta7
Bootstrap 4.5.3 used in Joomla 4.0.0-Beta7-dev
Bootstrap 4.5.2 used in Joomla 4.0.0-Beta4 to 4.0.0-Beta5
Bootstrap 4.5.0 used in Joomla 4.0.0-Beta1 to 4.0.0-Beta3
Bootstrap 4.4.1 used in 4.0.0-Beta1-dev
Bootstrap 4.3.1 used in Joomla 4.0.0-Alpha7 to 4.0.0-Beta1-dev
Bootstrap 4.1.3 used in Joomla 4.0.0-Alpha5 to 4.0.0-Alpha7-Dev
Bootstrap 4.1.1 used in Joomla 4.0.0-Alpha3 to 4.0.0-Alpha4
Bootstrap 4.0.0-beta.2 used in Joomla 4.0.0-Alpha1 to 4.0.0-Alpha2
Bootstrap 2.3.2 (custom modified) used in Joomla 3.1.4 to 3.10.x
Bootstrap 2.1.0 (custom modified) used in Joomla 3.0.0 to 3.1.1

This is a frequently updated list of Bootstrap used in Joomla. The Bootstrap versions used in Joomla 3 are not official, they are custom modified. Custom modified versions of Bootstrap 2.1.0 are used in Joomla 3.0.0 to 3.1.1, while custom modified versions of Bootstrap 2.3.2 (the latest of the 2.x series) are used from Joomla 3.1.4 to 3.10.x. In a few words, all Bootstrap versions used by the Joomla 3 core, are custom modified versions of the Bootstrap framework 2.x series.

We can also see this as a comment on each file:

/media/jui/js/bootstrap.js
/media/jui/js/bootstrap.min.js​

* Custom version for Joomla!

Using modified versions of the library is not a good practice and this has changed in Joomla 4 and 5. In Joomla 3 the site admins/webmasters were locked to only use that custom modified bootstrap version that comes with the Joomla core. Since javascript functions have been changed inside the bootstrap.js and bootstrap.min.js files, loading any official Bootstrap version other than the one of the core, causes serious functionality problems in the Joomla administrator area when the default template is used. The official Bootstrap 2.3.2 can be used in the Site (Front End) area without fear, although it is a very old version released in 2012. Any Bootstrap 5.x, 4.x or 3.x series version would cause javascript functionality conflicts if used in Joomla 3.

Recommended Joomla Extension: Eorisis Elements available in both Free/Pro editions.