Bootstrap: How do I identify the Bootstrap version?

Method 1 - Very Simple

In Package.json - you'll see bootstrap package installed with version mentioned.

"dependencies": {
    // ...
   "bootstrap": "x.x.x"
    // ...
}

Method 2

1. Open node_modules folder and under that
2. Search and open bootstrap folder
3. Now you'll be able to see version number in the following files
   • package.json
   • scss/bootstrap.scss or css/bootstrap.css
   • README.md

In the top of the bootstrap.css you should have comments like the below:

/*!
 * Bootstrap v2.3.1
 *
 * Copyright 2012 Twitter, Inc
 * Licensed under the Apache License v2.0
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Designed and built with all the love in the world @twitter by @mdo and @fat.
 */

If they are not there, then they have probably been deleted.

VERSIONS:

You can review version history here. Backward compatibility shouldn't be broken if the source is v2.0.0 (Jan 2012) and above. If it is prior to v2.0.0 there are details on upgrading here.

You can also check the bootstrap version via the javascript console in the browser:

Looks like this solution works better with bootstrap 4/5.

bootstrap.Tooltip.VERSION // => '5.2.0'

Credit: https://stackoverflow.com/a/66194641/1608226 (be sure to give upvotes).

This version works best for Bootstrap 3. it can also work for Bootstrap 4, but may not work for Bootstrap 5.

$.fn.tooltip.Constructor.VERSION // => "3.3.7"

Credit: https://stackoverflow.com/a/43233731/1608226 (be sure to give upvotes).

Posting this here because I always come across this question when I forget to include JavaScript in the search and wind up on this question instead of the one above. If this helps you, be sure to upvote that answer as well.

Note: For older versions of Bootstrap (less than 3 or so), you'll proably need to search the page's JavaScript or CSS files for the bootstrap version. Just came across this on an app using bootstrap 2.3.2. In this case, the (current) top answer is likely the correct one, you'll need to search the source code for the bootstrap to find what version it uses. (Added 9/18/2020, though was in a comment since 8/13/2020)

Edit 9/2/2022: Added solution that works better for Bootstrap 4/5.