We get asked about this a lot, usually by someone who's mid-redesign and frustrated. The site was supposed to take a few weeks and it's been two months, and the reason is that the content and the design were built as one thing, so touching either one means touching both.
A headless CMS is just the arrangement where you don't do that. The content lives in its own system.
The website is a separate system that reads from it. They're connected, but they aren't the same thing, so you can rebuild the front of your site without going anywhere near the content, and you can point a second thing at it later (an app, another site, whatever) without copying anything by hand.
That's the entire concept. The long lists of benefits you'll find on other pages all come back to that one separation.
What it changes in practice
The redesign problem above mostly goes away, since you're swapping the front end and leaving everything behind it alone.
The other thing people notice is that marketing stops waiting on developers. If your pages are assembled from reusable blocks (a hero, a features section, testimonials and a CTA), then building a new landing page is an afternoon's work for whoever owns the campaign, not a ticket in someone's sprint.
I'd rather be upfront about the limits, though. Headless doesn't make your site fast and it doesn't improve your rankings. It gives you control over both, and what you do with that control is on whoever builds the frontend. And if your website is five pages and a blog that rarely changes, honestly, this isn't a problem you have. WordPress is fine.
Where Stak fits
Stak is our own headless CMS. It is fully open source, self-hosted and free, built by the team at Koncepts Lab. Four things worth knowing before you look further.
It doesn't assume you're publishing articles. Most CMS platforms are built around blog posts, so the first time you need a product with variants, specs and pricing, you end up forcing the data into a shape that doesn't fit. Stak lets you define the structure you actually need.
No plugins, deliberately. Forms, media library, multiple languages, tags, roles and permissions, activity logs and spam protection are all part of the product. If you've ever inherited an old site, you know the plugin folder is usually where the trouble is. Extensions that stopped being maintained, updates that fight each other, security holes in code nobody's read in years.
You own the whole thing. It runs on your own servers, or AWS, or Google Cloud, or a serverless setup.
The code and the data are yours. There's no licence fee and no usage-based bill that grows as your traffic does.
Free, and it stays free. You get the full codebase, updates and community support without paying anything. If you want us involved directly for setup, custom features, migrating from an existing platform or performance work, that's $15/hour with no contract. The only condition attached to the free version is that you keep a "Powered by Stak" credit and don't resell it as your own product.
How to decide
The useful question isn't whether headless is better in the abstract. It's where your content has to go over the next couple of years.
If it's one website that'll look broadly the same, you don't need to change anything. If there's an app coming, or a few different properties, or a catalogue that's outgrowing where it currently lives, then separating content from design now is much cheaper than doing it after the fact.
Beyond that, the things worth checking are whether the system can hold your content in the shape your business actually uses, who owns the data, and what the cost looks like once you've grown.