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Show HN: Capsule – Single-file web apps that save their data into SQLite (withcapsule.app)

1 points by bashtian ↗ HN
Hey HN,

I always had the problem that building HTML pages is really simple now, but trying to save data required hosting it somewhere, and sharing it afterwards was not easy. Over the last few months, I've been building an app called Capsule (it’s also the file extension name) written in Rust with Tauri 2.0 that allows packing an HTML app and its data into a single SQLite file.

The HTML file and any related assets are directly embedded in the database. User data can either be saved as a localStorage key/value store or via a MongoDB-inspired collections API as documents, saved in a table in the file. You can also save other assets, like PDF files or images, directly in the database to keep different documents together. All data can be easily exported to CSV or JSON if needed.

Privacy and security were a big priority for me, so documents cannot do anything out of the box. They don’t have direct access to the file system and they require permission to access the internet. The permission model is still something I’m working to improve. Capsule documents can also use local or remote AI models for document specific AI features.

One downside with this approach is that multiple people working on it will create different copies. To make it possible to merge different copies of the same file, each data entry has a unique UUID and timestamp.

I’m planning to open up the file format specification for the 1.0 version of the app so other apps can read or write Capsule files.

You can try it out in the web preview at https://withcapsule.app/preview with pre-built templates or use any AI provider of your choice to create a custom, Capsule-optimized app by using the following prompt:

"Please read the app wizard instructions at https://withcapsule.app/prompt.txt and help me design an app.“

I’m still working on the file format but there are migrations for each new version, so data should never be lost when using newer versions of the app in the future. Please let me know if you have any ideas or use cases where this might make sense or does not work.

114 comments

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andai
That's pretty cool. But who is this for? What problem does it actually solve?

How would I know if I need this, vs something else?

bashtian
If try to do data management in Excel or need to download an app just to save some recipes, this could be an alternative. For example you can track time and billing with a nice UI without requiring a SaaS subscription. You can try some examples in https://withcapsule.app/preview
lewisjoe
This is great. Curious: this requires users to have a host app installed on their machine that can read .capsule file right? Won't that be a point of friction for distribution?

Isn't html/css a better distribution mechanism as most computers already have the tech to run them?

lukasbm
I imagined the capsule website would be able to either convert or directly run/open them
[dead] bezko
[flagged]
eleventen
You can get a cheap approximation of this with chromium browsers + Filesystem API and a PWA manifest for that native-ish feel. AI has reignited my interest in building based 100% on browser native features.

https://developer.mozilla.org/en-US/docs/Web/API/File_System...

bashtian
If you want to distribute apps to many users this would probably be a better solution. The main benefit of Capsule is the personal document like app. You create a capsule, move it to an USB stick, save it in your cloud storage and it's still the same document. Nothing has changed, not the UI, not the data. The document will stay the same.
ramon156
how is a filesystem supposed to prevent you from doing that?
al_borland
If it’s web native, anyone can just use it. If it’s a capsule, they first need to download the capsule app to associate the file extension with the OS and have it launch, right?

That feels like a big barrier, almost like a Java runtime.

gadders
>>Capsule packs your entire app — UI, data, and everything — into a single portable .capsule file.

I'm having Lotus Notes flashbacks.

p2detar
Indeed. But Lotus Notes actually had the design and data stored independent of one another and you had database templates. You could update your design without breaking the data, or even have entirely different design that works with the existing data model.

This capsule thing seems to store the design itself within the database, which is odd to me. I guess I don't get it at 100%.

dgf18
Many big companies are starting now to test agentic coding to automate business processes. This could be a nice tool to distribute apps for workflows that aren't big enough to justify the operational overhed of maintaining a traditional web app backend. Nice!
m-p-3
This sounds like the modern take on MS Access.
lolakutty
What is wrong with using IndexedDB?
bashtian
For saving data in the capsule file it would create complexity regarding migration handling when updating the HTML file to add a field to a form for example. Keeping the data schemaless makes it also easier for merging data or importing data from a CSV.
lolakutty
Doesn't indexedDB have builtin migration mechanism?

>Keeping the data schemaless makes it also easier for merging data or importing data from a CSV.

Not sure how it makes easier. There is always an implicit or explicit schema. IMHO explicit is often better.

fdeth
So, let’s do Visual Basic again, but this time with LLMs and web stuff.
blamestross
Seems very "packable into a standalone binary" but doesn't seem like that is a planned use case.
bashtian
The problem would be cross-platform support. In the end the capsule file is the standalone binary similar to a PDF or a Word document, you only need the viewer app to open any capsule file.
blamestross
you can trivially bake X binaries if you have the viewer app for each platform. This is the normal way to distribute software for cross-platform support.

I might just be hyper-defensive to any sort of vendor lock-in like a "viewer app".

tonymet
is the idea this would be hosted or run locally (like Electron)?
bashtian
This is for local document like apps. Tauri is actually using the OS webview instead of bundling Chromium like Electron. That's why the download is only 10MB for Mac.
tonymet
i like that idea. Anything that improves native OS UI, responsiveness (120hz) and reduces resources is a good idea.
redog
This seems ripe for an injection attack. Can it be inspected before running?
[deleted]
(comment deleted)
jawns
My take: If your app needs to update and preserve state (using SQLite or any other DB), it is probably not something you want to pass around as a bundled file.

Or at least, it's extremely limiting, compared with hosting it somewhere on the web, which is not that hard to do these days.

Think of the workflow: Any time the state changes, you need to email a new Capsule file to whoever else is using the app. And one would think the state would change at least occasionally, because otherwise there's little reason to use a DB.

Alternatively, you can just host it on the web, the DB state dynamically updates, and it's automatically available to anyone with app access. Isn't that a lot simpler?

Reviving1514
Why not on a shared drive like dropbox?

Concurrent editing wouldn't work, though.

teraflop
Beyond "not working", concurrent editing is likely to silently lose data, or corrupt data, or possibly just fill up your drive with lots of "conflicted copies" that you have to manually reconcile.
dizzard
When I read about this project, it doesn’t seem like concurrency is much of a concern. I think it’s _supposed_ to be treated like sharing a document with someone else.

If a capsule is a recipe, like in one of the examples, that’s pretty cool. If a capsule is a recipe _manager_, then I think it would get messy.

latexr
> Isn't that a lot simpler?

You’re glossing over the recurring cost and annoyance of dealing with the hosting and having to secure the data. This way you just share and it’s local.

Sure, if you have to share data between people, your points are valid. But this seems like a way to build apps geared for individual users, like a notes or recipes app.

lateatdesk
Or the copies can go their own way. I could send someone an itinerary and they could change the dates or drop half the stops and add their own notes without needing to send an updated copy. Getting them to install another app just to open it might be a problem, especially if they only want to use it once.
tamimio
New way to deliver viruses just dropped! Great idea but it can be abused for sure.
bashtian
The HTML files does not have any permission to access anything on the file system. Ideally the whole app will be running inside a sandbox on desktop, for mobile apps this will be the default anyway.
sigmonsays
if state is best shared, why keep it w/ the code?

You're gonna end up having to build a complex state sync system to a central DB anyways...

olaulailadila
An idea for a killer feature: Make it so that auhors can expose their capsules to the internet, and the people whoe wants to use them(lets call them users) can type the name(lets call it address) of the caplsue into the app, and your program will pull that capsule in the the users device..
derpyzza
wow, that sounds revolutionary.
ligarota
Hear me out. Here is the name

PWA : Probably Web Again

saejox
nice. we should call it web, like spiders' web all connected.
dzink
Looks useful, but the Mac download shows "“Capsule” is damaged and can’t be opened. You should eject the disk image." and then you realize it could be ripe for malicious payloads as well.
xd1936
"No cloud. No accounts. Just share it." close tab
j-pb
yes yes we get it, you don't like AI ...
mionhe
Can you elaborate a little?
al_borland
It reads like the whole thing was vibe coded and 0 work was done beyond what the AI spit out.
razerbeans
I love this idea! One of the fallouts from widespread AI adoption that I've seen: They're very good at creating visual artifacts, but if you ever have to provide data in those artifacts, you don't really have a great way to share it without hard coding it.

> One downside with this approach is that multiple people working on it will create different copies. To make it possible to merge different copies of the same file, each data entry has a unique UUID and timestamp.

This was the first thing that popped up in my mind: Changes stemming from two sources and reconciling them. I see that you have a statement about how to handle data entry from different sources, but I don't see exactly how those are reconciled? For instance, if two users have a copy of the .capsule and make changes, then want to share their changes with the other, you have two individual .capsules with different data.

How do you merge them?

bashtian
Each document record is saved with UUID and timestamps. When deleting a record the data is removed but the record keeps a tombstone so only the ID remains. For conflicts currently the newest one is used, but there will be a merge like UI in the future to confirm which one to use.
rc-1140
This is a really cool and practical idea! Some of my first professional efforts out of college were writing Python mini-apps with Tkinter to replace "abused" Excel spreadsheets. One of my friends working in sales might benefit from something like this, I'll send it his way.

I don't know about the stability/market value of this if you intend to turn this into something that attempts to make money, however. Said friend is currently using stuff like Gemini to generate HTML mini-apps as well; while he's not storing anything in databases, he's able to generate receipts and other things for essentially free.

Jonovono
“Capsule.app” is damaged and can’t be opened. You should move it to the Trash.
thesurlydev
With the battle of AI versus human agency raging I have a prediction that local-first desktop apps are going to make a comeback. It's nice to see something like this make it easier.
rglover
I agree and would love to see a shift back to what we had circa ~2009-2010: high quality, desktop and platform-specific apps that you could just pay for once (the best variant for everyone being an app that works indefinitely, but only receives updates if you renew your license every year).

The whole shift to SaaS has decimated software quality and has made most tasks a nightmare to complete (or at best, an obstacle course of multiple tools and "upgrades" and other bs).

dsparkman
I know that I personally have a handful of personal local only apps under development, that in the past I would have reached for a web solution.
explorigin
In preparation for the upcoming [Android lockdown](https://keepandroidopen.org/) I've started vibe-coding some PWAs for apps that I like so I can have a webby version of them with no ads and no Google/iOS lock-in. I like this, it feels like a good direction.
krapp
It's depressing that everyone decided Electron was the final form of all applications and that native apps were dead until AI came along, and if native apps come back it will only be as vibe-coded slop. It's like we've just moved from once circle of hell into another.
domh
I wish there was a way to see the underlying HTML/JS and schema of these container files. Maybe you can on the desktop app? But it would be cool to see what's happening under the hood.

Do you have any plans to do merging of two versions of the same app? E.g. I send a todo list to someone, they mark some things as done and send it back to me. Will that merge into my copy if I've added some more items or would it open as a "fresh" app?

bashtian
Merging works already but is a little bit hidden under the data editor function in the Capsule edit menu. Currently the last record update wins, but a merge UI is planed to do manual conflict resolving.