Alternatives to Flexx?

[matkuki]

Hi @almarklein and anyone else who wants to chime in,

Are there any alternatives that work in a similar fashion to flexx?
They do not have to be Python based, any other language is fine, but just a similar principle to how flexx works:

• minimal javascript, mostly just for custom bindings and custom functionality
• seamless browser<->backend connection
• simple layout system
• ...

Thanks

[almarklein]

It depends a lot on what you want to do, I guess. I think one big "feature" of Flexx it is being Python, but from what I read you're open to other tools too. I am quite impressed with Svelte (only played with it so far). II think it mostly solves a different problem, but it's pretty slick, and if you combine with CSS (i.e. flexbox) you have a really nice basis to build interactive apps.

[matkuki]

Hey @almarklein

Thank you for the information. I really adore flexx, that should be obvious by now 😊.
But there are a few things that are causing me to worry about the future of the library (these are all point for usage of flexx on Windows):

• As mentioned in is this project dead? #752 , no active development. This isn't a big issue, but it's still there. Lot's of little things that could be improved:
  • Some widgets have rough edges or weird / hidden behaviour, as I discovered and reported here. Like scrollbars in Layout's, quirks in the Python-Javascript layer with PyWidget / Widget / Component, ... Thanks again @almarklein for solving the issues with me 🎉
  • Built-in security measures would be nice to have. A good tutorial on how to make a solid and secure internet facing application would be great. A simple beginner friendly tutorial.
• Compilation Python-To-Javascript is getting slower and slower with newer Python versions. Example: one of my flexx apps with Python3.7 starts in about 4 seconds, but with Python3.13 it takes more than 10 seconds - No changes in anything except the Python version.
• Something changed with Python versions >=3.10 that changed the behaviour of the async event loop (this is Windows specific, haven't tested it on Linux!), that freezes every call to asyncio.get_event_loop().call_later other than on the main thread. This is worrying for applications that use this heavily, as some functionality doesn't work without any errors / tracebacks.

flexx is still my favourite web framework (by far!!!), but not having at least some maintenance on it makes me a bit hesitant to use it for more projects. I'm willing to do fixes and upgrades in any aspect of the library, but I would need lots of guidance in getting to know it's internals.

Thanks again @almarklein

[almarklein]

Thanks for sharing @matkuki. I understand your worries.

Personally, I have moved on to other things and don't want to spent much time on Flexx anymore. I still find it an interesting project though, and I can try to find time to do some minimal maintenance or advice to e.g. keep adjusting to new Python versions.

I'd be happy to give you (or someone else) admin rights so that someone can take a leading role in keeping Flexx going, and shaping it to their vision. And I can definitely chime in now and then.

Compilation Python-To-Javascript is getting slower and slower with newer Python versions. Example: one of my flexx apps with Python3.7 starts in about 4 seconds, but with Python3.13 it takes more than 10 seconds - No changes in anything except the Python version.

I did not know this. That's not what I would have expected 🤔

[Konubinix]

I did not try it, but it seems to me that https://github.com/reflex-dev/reflex is the closest alternative I could find. It seems a bit less flexible though

[TheJeffah]

Hi @almarklein,

I recently discovered Flexx, and I was really excited because it’s exactly the kind of tool I had been looking for: a way to build client-side logic GUIs in Python. Unfortunately, it seems I arrived a bit late, as the project hasn’t been updated actively for some time.
I wanted to ask if there is any possibility to continue updating or maintaining the project, even in a minimal way. Many developers like me rely on it and truly appreciate the unique approach Flexx offers.

Thank you very much for your time and for creating such an innovative project!

Best regards,
Jefferson

[almarklein]

I'm happy to review small PR's e.g. to keep Flexx working on new Python versions, and to do an occasional release.

If someone really wants to take this project further, I suggest creating a fork and moving from there under a different name. Call it flexx2 if you want. I'd be happy to add a link to the readme.

[TheJeffah]

Hi @almarklein,

I like the idea and I'll take a look at the project. I don't have time to start right now, but since you allow me to work on it, I'm interested. I'll first study how the project is; when I feel ready to move forward, I'll get back in touch.

Best Regards

[HackYardo]

Have u try NiceGUI, a python web ui library with 15k stars?
I know it during 2022,
but one may know a bit of js vue/react to design app layout,
and the speed is a bit slower than expect.
However, now 2026,
nicegui is much faster.(and for sure, much slower than C/Rust)
If u prefer python like me, I suggest it.

[TheJeffah]

Thanks for the suggestion! I've actually tested NiceGUI and several others, but the fundamental issue is that nearly all of them are server-side - every interaction requires a round-trip to the server, which is exactly what I'm trying to avoid. What I need is what Flexx uniquely offers: client-side logic execution, where Python code is transpiled to JavaScript and runs directly in the browser, with server communication happening only when strictly necessary (database, file I/O, etc.). This gives instant UI responsiveness, lower latency, and reduced hosting costs, all while still writing pure Python. I genuinely believe this is an underserved niche - a tool that compiles Python to lean JavaScript, runs everything client-side, and minimizes server dependency would be incredibly well received. I've considered building something like this myself but don't have the time right now, so I'm still searching.

[niki-sp]

https://github.com/kkinder/puepy HTH Niki

[TheJeffah]

The idea is great and it’s really very close to what I’m looking for. From what I’ve seen, though, PuePy relies on PyScript (Pyodide), and that raises concerns about browser performance because of the relatively heavy layer that needs to interpret/translate everything at runtime. Conceptually, this is exactly the direction I have in mind — running the logic on the client and minimizing server dependency — but for day-to-day use it also needs to be fast. In any case, thanks a lot for the suggestion! 👍

[almarklein]

Python code in Pyodide/PyScript runs slower than JavaScript, but it runs at nearly the same speed as normal Python. Pyodide is CPython compiled to wasm, so the only extra overhead (and warmup) is in the wasm.

PScript is faster because it compiles directly to JS, that is true. The cost of that is that the code you are writing is not actually Python, and it can be a bit confusing, because it's hard to tell what Python things you can actually use and which not. This gets more annoying in bigger projects.

For what it's worth, I created Flexx and PScript when Pyodide did not exist yet. If I would create something like Flexx now, I would probably just use Pyodide ...

[TheJeffah]

Excellent news! I didn’t know about PScript before. I had only heard briefly about Flexx, and I also didn’t realize that this project was yours.

Personally, I think the delay and overhead of PyScript are a huge drawback. For me, Python with WebAssembly is still not well solved. My impression is that, like with other languages, there should ideally be something that simply compiles Python to WASM and that’s it. Bringing the whole interpreter into the browser feels like unnecessary overhead — but that’s just my opinion.

Until someone brings that idea into a practical project, PScript seems to be exactly what I was looking for. Let me explain: JavaScript is much simpler and more direct in the browser, but I really don’t want to deal with two programming languages. From what I quickly saw in the PScript docs, I can encapsulate JavaScript when needed, manipulate the DOM, and implement logic. In the end, everything is transpiled to JS and runs natively in the browser.

I understand that I’ll probably have some initial work encapsulating some JS parts, but that’s part of the trade-off 🙂. The advantage is that this opens many possibilities: I could wrap JS from different frameworks and still work mainly in Python with PScript.

So effectively I get the speed of JavaScript and the ecosystem of JS frameworks, while writing most of the logic in Python.

If there were a solution that compiled Python directly to WASM while still allowing easy DOM manipulation and application logic, that would probably be unbeatable.

I’d also like to make a small suggestion — hopefully not sounding presumptuous. The name “PScript” may create a branding challenge, because many searches tend to return PyScript instead. Since the names are very similar, a different name might help the project become more discoverable. Just a suggestion 🙂

Thank you very much for the news. Now I’ll try to find some time to study PScript more deeply and experiment with it.

Best regards!

[almarklein]

If there were a solution that compiled Python directly to WASM while still allowing easy DOM manipulation and application logic, that would probably be unbeatable.

I agree, and this has been a dream of mine for more than a decade 😄 But it will never happen. I have let go of that idea. (My dream now is a new language that is nearly as dynamic as Python but runs explicitly on wasm.)

It is simply impossible. Python is a dynamic language, so you cannot simply compile it. There are loads of projects that try, but you always have to sacrifice something, and in effect you get a new language that looks like Python but is not. For example:

• Numba is particularly good at optimizing code that operates on arrays, but it won't optimize generic code well.
• Cython requires fully typed code.
• SPy explicitly targets wasm, but it's limited Python.
• Similarly, PScript looks like Python, but it's actually JS with a Python syntax.

but I really don’t want to deal with two programming languages.

That was indeed my intention. And for small projects it works! However, I found that my awareness of how to write performant code, and what you can actually do, is different than when you write real Python. So in effect you still have two languages, except they look the same (and that can actually be confusing).

So yeah, I still think PScript is pretty awesome, and you should go ahead and have fun with it, but it's not a scalable solution in my opinion.

The name “PScript” may create a branding challenge, because many searches tend to return PyScript instead.

PScript was created years before PyScript. The fact the PyScript shows up in searches more is probably because it's a more mainstream solution.

[niki-sp]

On 3/6/26 10:27, Almar Klein wrote: *almarklein* left a comment (flexxui/flexx#753) <https://github.com/ flexxui/flexx#753#issuecomment-4010303046> If there were a solution that compiled Python directly to WASM while still allowing easy DOM manipulation and application logic, that would probably be unbeatable. I agree, and this has been a dream of mine for more than a decade 😄 But it will never happen. I have let go of that idea. (My dream now is a new language that is nearly as dynamic as Python but runs explicitly on wasm.) It is simply impossible. Python is a dynamic language, so you cannot simply compile it. There are loads of projects that try, but you always have to sacrifice something, and in effect you get a new language that looks like Python but is not. For example: * Numba is particularly good at optimizing code that operates on arrays, but it won't optimize generic code well. * Cython requires fully typed code. * SPy <https://github.com/spylang/spy> explicitly targets wasm, but it's limited Python. * Similarly, PScript looks like Python, but it's actually JS with a Python syntax.

Maybe Mojo will add WASM backend Niki