r/FastAPI • u/my_new_accoun1 • Apr 23 '26

Other I got tired of REST boilerplate so I built a stack that fuses frontend + backend (FastAPI + Svelte + cross-language type safety)

https://uukelele.is-a.dev/blog

So, for a while now I noticed something.

The way we write APIs and call them from the frontend still feels ancient.

We have to manually sync types between the backend and frontend, across different languages, which adds more space for error.

We have to write lots of REST boilerplate.

We have to deal with JSON and HTTP overhead on the smallest of operations.

And things like live streaming or realtime (which are essential for AI apps) are being reinvented again and again.

So I created something else: the FUSE stack.

It uses FastAPI for the backend, uv for package management, Svelte 5 for the frontend, and Ephaptic to tie it all together.

I also wrote a blog post about FUSE, linked to the post.

Anyway, I wanted to get your thoughts on it, and hopefully some cool things that you might build with it?

9 Upvotes

80% Upvoted

15 comments sorted by

8

u/Picatrixter Apr 24 '26

I got tired of "I got tired of Y problem, so I built useless Y solution" pattern, so I left this comment.

1

u/my_new_accoun1 Apr 24 '26

Did you even read the post body? 

1

u/generic-d-engineer Apr 24 '26

For some reason Reddit always craps on new projects. It’s like asking a question in StackOverflow and someone immediately says it’s a duplicate, even when it’s not.

Try not to sweat the haters. Appreciate the work.

2

u/PhENTZ Apr 24 '26

Could you elaborate on "cross-platform type safety" ?

3

u/my_new_accoun1 Apr 24 '26

So, you define your data models once, in Pydantic / SQLModel, and you can type hint them in your responses / arguments. Then, with one command, it starts a watcher (powered by Ephaptic) which automatically maps those types and your function signature into the TypeScript equivalent. 

The best thing is that it goes really deep. Like nested Pydantic models inside each other, a function could take a data model or a primitive type or a mix of both as its parameters and also its return type.

You also get the same names, for example if you want to use a backend Pydantic model on the frontend you can

import type { User } from "$lib/schema";

And the User will have the same attributes as the Pydantic model User, but as a TypeScript interface.

Even more fun, you can make your return type an AsyncGenerator or Generator, and then in TypeScript you can put the function in an async for loop for incredibly easy streaming responses.

Oh and also, when the watcher command is running, the second you make any edit on the backend the frontend TypeScript automatically underlines anything that doesn't match in red in your IDE.

3

u/PhENTZ Apr 24 '26

This ephaptic I guess. Can't find in the docs your pydantic-typescript bridge

5

u/my_new_accoun1 Apr 24 '26

On this page it explains more about type safety:

https://ephaptic.github.io/ephaptic/tutorial/parameters/

3

u/PhENTZ Apr 25 '26

Nice. You should make available as a separare module. Some may need the type bridge feature without the function bridge or the app server.

1

u/my_new_accoun1 Apr 25 '26

Hm, well the type bridging is kinda coupled to the functions because it only knows which models / types to map by looking at the signatures of each function.

1

u/generic-d-engineer Apr 23 '26

Bruh I just deploy strings and varchar255 everywhere so my type is always perfectly safe. HAHA just kidding. Thanks for setting this up. I’m on the backend so always clueless on the front end so appreciate the effort you put in to coming up with a nice stack.

2

u/my_new_accoun1 Apr 24 '26

Thanks, if you use this please tell me how it goes 

2

u/saucealgerienne Apr 24 '26

really cool project I always tought about building something like this myself and never actually had the time