Launch HN: Bitrig (YC S25) – Build Swift apps on your iPhone
52 comments
·August 27, 2025null
kylemacomber
On a personal note, I wanted to thank the HN community. I’ve been reading HN since college (for over 15 years now!) and it’s been formative in my development as a software engineer and leader.
I don’t pipe up very often, but I visit HN almost every day. Many of the books I read, blogs I frequent, and podcasts I listen to, I found via HN. I think it’s fair to say, if it weren’t for HN, that Bitrig wouldn’t be Bitrig and SwiftUI wouldn’t be SwiftUI.
rcarmo
I wish Apple would let us build and install these apps locally without fuss.
FlamingMoe
Neat. I just tried it out and one thing I was pleasantly surprised about was the styling it came up with. It was sleek, and it did not have the purply gradienty tailwindy styling that I always get from Claude. Did you do much to adjust the prompt for custom styles?
kylemacomber
Styling apps is an area we're excited to spend time exploring. Today in our system prompt we say "ALWAYS make the design Apple-like. Use clean typography and consistent padding/spacing." However, tbh it's not something we carefully tested.
For the most part, I think the look and feel of the apps benefits from SwiftUI baking Apple's design system into the defaults so heavily.
jaccola
It doesn't seem like this is the direction you are going, but this feels like what Siri could become (though I have little faith given the history).
With your sunscreen example, I should be able to just ask Siri to do exactly this, and it could tap me in my pocket, show me a custom UI to log periodically and then disappear.
Not sure on limitations of APIs on iOS but definitely feels like there is space for a better voice assistant, just like how Raycast have created a better Spotlight on Mac.
Looks very cool so far!
jacobx
Yeah, I think that whole area of dynamically generating UI is really interesting. And having a Swift interpreter like we're using would unlock doing that with native UI components.
Our background is more in making developer tools, so bitrig was the first product we were excited about, but I think there's a lot of overlap with dynamic UI generation, and we'd love to explore that too.
saaaaaam
Doesn’t work at all for me.
Entered my my prompt… It did a bunch of stuff - apparently initially focused on making me an app icon which I don’t really care about.
I moved away from the app, went back and everything had gone and my prompt was just sitting there by itself.
I said “please proceed” and it opened a new chat, did the same thing. It was doing stuff, I moved to something else, went back, everything vanished.
So that’s two of my five free messages zapped. And all of my patience.
jacobx
Sorry about that, I reset your free messages for the day, so you should be back at 5.
Moving in and out of the project while messages are sending is a more fragile area of the app and we have some bugs to fix there.
markden
First, as a non-developer geek -- super fun.
What happens if you go over 100 messages/month?
I just burned my 5 free messages to get a simple toggle button working that just says "win" (with animated fireworks!) and "lose". I'm sure I'm not an efficient prompter, but it seems I'd knock out 100 messages easily in an afternoon, which looks to be the monthly limit at $20/mo.
(This is coming from someone who has no idea how expensive it would be to 'vibe code' using something like Claude ... so it may be an entirely unfair assumption that you could chat with this 'unlimited' for $20/mo ... that's what I have in my head as 'reasonable' only because that's what I pay for Gemini or ChatGPT and, for all intents and purposes, it feels 'unlimited'.)
kylemacomber
Don't tell anyone, but once you're on the paid plan we're not actually enforcing the 100 message limit right now ;)
We're still in the learning phase, and are going to adjust the plans based on exactly the kind of considerations you're raising
markden
Your secret is safe, hah! It's almost like you need an intermediate 'cheap/dumb' AI as a proxy to flesh everything out ahead of sending it off to be coded ... something that crisps up all the requirement and ultimately crafts a more cost-effective and likely all-around-better prompt. Even being semi-technical, I'm always surprised how much the details matter when describing something to AI (e.g., the fireworks should only explode _outward_, not inward, lol). Thanks!
kylemacomber
There's a lot I want to do to improve the prompting experience. As I mentioned in the original post, it's very simple right now.
There's a lot of inspiration we could (and probably will) draw from other products (e.g. Cline's Plan vs Act modes) to build what you're describing.
It can also be really fun and productive to just rapidly iterate on what the AI gives back, without having to take the time to describe it all up front. Sometimes this approach can lead to a new directions you might not have thought of.
avarun
Seems like a cool concept! I downloaded and entered an email address but haven't received a verification code yet after 10 minutes. It's an Apple Private Relay email if that matters.
Also, side note: magic link or email-based OTP login is by far my least favorite method of login, especially for a phone app. It's cumbersome, annoying, and completely unnecessary now that passkeys exist. Barring that I'd still rather use email/pw login any day of the week.
jacobx
That's weird, can you try hitting back and then the forward arrow again? That should resend the email. If that still doesn't work, let me know and we can investigate on the backend.
We've definitely been hearing from users who don't like OTP, we'll try to get additional login options added soon.
avarun
I eventually had it come in another few minutes after I left the comment. And sounds good! I’ve had good success with Clerk for auth in the past.
Now that I’ve gotten to play around with the app I have to say I’m impressed with how smooth it feels and how well the Swift interpreter works (at least on the basic prompts I’ve tried). One suggestion: allow toggling between an “edit” mode and a “view” mode. The latter would full screen the app and hide the interface for follow up prompts, etc. that would make it easier to approximate how the app will behave in the wild.
I could see this eventually turning into sort of a social platform for mini-apps, by the way! Where users don’t even necessarily need to publish to the App Store if they’re just creating something for themselves and a few friends.
jacobx
We probably need to make this more discoverable, but if you keep swiping down on the prompt area, you can swipe it completely off screen and your app will be full screen (with a small movable floating button to exit).
I really like the idea of a platform for people sharing mini-apps! It would be great if people could make lightweight specialized apps for different niches and share them with less friction.
sunnybeetroot
That’s interesting, on a desktop device I would agree. However having to create an account on 1Password for an app I just want to try is a pain compared to using Apple’s Hide my email and entering in the OTP. I get that it didn’t work for you but it did for me.
avarun
It’s 2 extra button clicks to generate a password and save it on 1Password, and you never have to leave your current context.
Versus for email OTP you have to switch to your email client, find the email, perhaps refresh a few times waiting for it to come in, click into the email once you see it, highlight the OTP, click copy, then switch back to the app and finally paste. I don’t understand how anybody could possibly prefer it.
HellsMaddy
Very cool! Was it difficult to get Bitrig approved on the App Store? If I had to guess just based on the idea, it seems like the sort of thing Apple would take issue with.
kylemacomber
Heh... it definitely wasn't an overnight approval. However, Apple has relaxed the guidelines for developer tools compared to the early days of the App Store. If you look today there are Python IDEs, Jupyter Notebooks, and various other apps that execute user generated code. The key guideline to be mindful of is 2.5.2.
ripped_britches
I love what you guys are doing but highlights how absurdly hard iOS development is compared to web
travisgriggs
I don't share your assessment. Is it because I did iOS apps before web apps? Curious how many others feel the same?
Seems like a reasonable poll question: Which is harder: web app development or native app development?
I was telling a younger colleague the other day how back in the day, I was "competing" with a peer at a company doing nuclear design software (Siemens Power Corp at the time). I was doing it in VisualWorks Smalltalk, he was doing his in straight C and X Windows. Competition aside, both of us built multi window complex graphical design tools that front ended heavy duty simulators, managed various batch jobs, tons of IO, parsing, and lots of color graphic drawing (mine was for fuel assembly (pin and axial enrichments) design, and his was for core layout (where the assemblies go during each reload)). The graphics were simpler (no antialiasing, any alpha we did with clever dithering tricks, not much in the way of animations, though we did each roll some). Both even stored /retrieved into a sort of database (a homegrown data versioning system). But... it was just one of each us for each "app".
Sadly, all Ux development seems orders of more magnitude complicated and beuqacratic now days. Some things are easier and vastly simpler than they used to be, and yet, the sum result is more difficult. I'm not exactly sure why.
jacobx
Totally agree, we have a lot of ideas for how to make the experience better.
WhitneyLand
Hey Kyle, looks very cool!
- If Bitrig can do things like let your app have editable data, or make rest api calls, etc. it would be nice to see a little more in the demo video.
- Sounds like you don’t have an expensive mic/studio for recording, but luckily this is free and can work wonders for your audio: https://podcast.adobe.com/en/enhance
Best of luck with the launch.
kylemacomber
Ya, I agree it makes sense for us to record a more tutorial length demo at this point and we can show off things like that.
Thanks for the tip about the mic. Fun fact: it's me in the video, but it's Jacob doing the narration :P
sukh
I’ve been playing with the TestFlight build and it’s really solid. Can you share any under the hood details of how the system is able to accurately map the loose prompt to fully native SwiftUI components. Mostly curious because I’d love to also build internal data dense apps typically better suited for desktop.
Great work and I hope to become a paying customer soon!
jacobx
Yeah, the prompt is just asking Claude to generate a SwiftUI iPhone app. The recent models have been able to generate really good Swift code, so we just have a set of best practice instructions we've been accumulating (telling it to make an app with @main, pointing it to/away from some APIs, encouraging it to persist things in UserDefaults, etc).
I think most of that would work pretty well for making SwiftUI desktop apps too.
w10-1
It would be lovely if the community had this knowledge about API's to avoid and approached to adopt. SwiftUI programming is a tightrope walk of stuff that works over a chasm of time lost to testing.
Hi HN, we’re Kyle, Jacob, and Tim. We’re building Bitrig (https://www.bitrig.app).
Bitrig lets you create native Swift apps for your phone, on your phone, just by chatting with AI. It’s like Lovable for iPhone apps.
Here's a video of Bitrig in action: https://youtu.be/CUlWhF3ERME
We created SwiftUI at Apple to help developers make better apps with less code. Bitrig lets anyone build at this level of polish. If you've thought about making an iPhone app, Bitrig is the easiest possible way to get started with Swift.
Bitrig uses Claude Sonnet 4.0 with a simple system prompt and tool definitions to generate native Swift code. Normally running this on an iPhone would require compiling and signing it with Xcode, and you can’t run Xcode on an iPhone. So we did something… creative. We wrote a custom Swift interpreter! Among other things this lets you instantly preview your app in Bitrig and share it with just a URL.
If you have a paid Apple developer account, you can connect it with Bitrig. We’ll compile your app on our server and upload it to App Store Connect, so you can distribute it on TestFlight or the App Store. This last step also gives you a fully optimized build of your app that you can install right on your Home Screen.
We think there’s something electric about building apps directly on your phone. We hope you give Bitrig a try!
We’re ingesting Apple’s SDK frameworks into Bitrig piece by piece. If you try to build something and hit a missing framework, let us know and we’ll prioritize adding it.
Download Bitrig on the App Store: https://apps.apple.com/us/app/bitrig/id6747835910