Bootstrap vs Flat UI
Which should you use? A side-by-side look at what each one does, who it suits, what it costs, how hard it is to set up, and where each falls short.
Open source · MIT
A free front-end toolkit of ready-made CSS and JavaScript for building responsive websites.
Open source · MIT
A flat-style visual theme and component set built on Bootstrap, for ready-made web pages.
The short answer
Choose Bootstrap if you need…
- Developers building responsive websites or web app interfaces quickly
- Teams that want a common design system with ready-made components
- Developers who prefer installing via npm, yarn, Bun, or a direct download
- Projects that need both LTR and RTL layouts, since the README says CSS supports both
Choose Flat UI if you need…
- Developers who already use or know Bootstrap and want a flatter visual style
- Designers prototyping a website who want a ready-made component look
- Small teams building simple marketing or landing pages quickly
- People who want a free MIT-licensed starting theme
Side-by-side
| Bootstrap | Flat UI | |
|---|---|---|
| Type | Library | Framework |
| Price | Free and open source | Free and open source |
| Licence | MIT | MIT |
| GitHub stars | 175k | 15.3k |
| Setup difficulty | Beginner | Beginner |
| How you get it | Install with a package manager | Clone and build from source |
| Main language | MDX | JavaScript |
| Last code update | 4 days ago | 16 months ago |
What each one is
Bootstrap
Bootstrap is a collection of HTML, CSS, and JavaScript code that gives web pages a consistent look and layout that adapts to different screen sizes. It is used by web developers who want to build interfaces faster instead of writing styles and interactive components from scratch. The README describes it as a front-end framework and points to a documentation site for details.
Flat UI
Flat UI Free is a set of HTML, CSS, LESS and JavaScript files that restyle Bootstrap's components with a flat, minimal look. Developers use it as a starting point so their websites have a consistent modern appearance without designing every button and form from scratch. It comes with a demo page, documentation and a Photoshop file for design work.
Best for
Bootstrap
- Developers building responsive websites or web app interfaces quickly
- Teams that want a common design system with ready-made components
- Developers who prefer installing via npm, yarn, Bun, or a direct download
- Projects that need both LTR and RTL layouts, since the README says CSS supports both
Flat UI
- Developers who already use or know Bootstrap and want a flatter visual style
- Designers prototyping a website who want a ready-made component look
- Small teams building simple marketing or landing pages quickly
- People who want a free MIT-licensed starting theme
Strengths
Bootstrap
- Widely used, with the README reporting about 175,000 stars on GitHub
- Provides both compiled and minified CSS and JS files plus source maps for debugging
- Released under the MIT license, which permits commercial use
Flat UI
- Free and licensed under MIT (with CC BY 3.0 noted in the README)
- Includes both compiled and minified CSS and JS files plus documentation and examples
- Builds on Bootstrap, a widely known framework
Not ideal for
Bootstrap
- Projects that want a highly custom visual identity without a default look, since the framework provides a recognizable base style
- Developers who need the latest stable release today, since the default branch is for Bootstrap 6 alpha development and the README directs Bootstrap 5 users to the v5-dev branch
- Non-developers looking for a no-code website builder, since it requires editing HTML and CSS
Flat UI
- Projects that need a large, actively expanding component library, since the README gives no sign of new releases beyond 2.3.0
- Anyone wanting a no-code builder; the README describes a code-based theme
- Teams needing SASS source files directly, since the README points to a third-party SASS port for that
Trade-offs
Bootstrap
- The default branch is currently a Bootstrap 6 alpha, so the README's quick start pins a pre-release version (6.0.0-alpha.1)
- The README does not describe component details in depth; it points to external documentation for that
Flat UI
- The README mentions a Bootstrap base but gives no version compatibility details
- Licensing is listed as both CC BY 3.0 and MIT, and the README asks users to link to the website, so check terms before commercial use
- The repository's last push and release info are not described in the README, so maintenance status is unclear
Getting started
Bootstrap
Install with npm (pre-release version shown in README)
npm install bootstrap@6.0.0-alpha.1Clone the repository
git clone https://github.com/twbs/bootstrap.gitFlat UI
Clone the repository
git clone https://github.com/designmodo/Flat-UI.gitInstall dependencies
npm installFrequently asked questions
What is the difference between Bootstrap and Flat UI?
Bootstrap: A free front-end toolkit of ready-made CSS and JavaScript for building responsive websites. Flat UI: A flat-style visual theme and component set built on Bootstrap, for ready-made web pages. Bootstrap suits developers building responsive websites or web app interfaces quickly, while Flat UI suits developers who already use or know bootstrap and want a flatter visual style.
Are Bootstrap and Flat UI free?
Bootstrap: Free and open source. Flat UI: Free and open source.
Is Bootstrap or Flat UI more popular?
Bootstrap has more GitHub stars (175k) than Flat UI (15.3k). Popularity isn't the same as fit — check which one matches your use case above.
What are other alternatives to Bootstrap and Flat UI?
Other options people compare them with include Tailwind CSS, Bulma, Materialize, Tabler, NES.css.
Keep comparing
Built from our catalogue entries for both products: open-source details come from each project's README (AI-assisted, refreshed weekly) and GitHub data; AI-tool details are editorial. Spotted something wrong? Let us know from either product's page.