Ghostty compiled to WASM with xterm.js API compatibility
github.com381 points by kylecarbs a day ago
381 points by kylecarbs a day ago
Holy shit Kyle. I had no idea you were working on this. This is amazing. Your patch is also very instructive on what you need me to do for you to make this more reasonable.
I'm guessing that performance of this relative to xterm right now isn't... the best, mainly because the way you're grabbing the viewport seems expensive. I'm curious though if you did any benchmarks?
One thing you probably really want to expose is the new RenderState API: https://github.com/ghostty-org/ghostty/blob/main/src/termina... You're doing per row line grabbing currently which is probably pretty slow. The RenderState API is stateful and produces the state necessary to create a high-performance, delta update renderer. It's what our production GPU renderers are now built on (but the API itself is compatible with any kind of renderer). It'd be better for you.
After all that, I'm very curious even at this rudimentary level what the performance on various benchmarks look like compared to xterm.js.
Excellent work!
We spent little time on performance so far, this is more of a POC that will hopefully become a drop-in replacement for xterm.js over time.
I'll swap it over to the new RenderState API and post some benchmarks!
Many kudos to y'all, we were shocked how simple it was to hack this together.
I built a macOS app that uses Ghostty and fzy to fuzzy search over Apple Note titles. It is working quite well for me.
Curious to know what makes this "a proper VT100 implementation in the browser, not a JavaScript approximation of one" -- isn't Ghostty also an approximation, just implemented in a different language? Seems unnecessarily pejorative to me.
Agreed. I removed "not a JavaScript approximation of one" from the README.
Fair clarification. Does Ghostty's WASM approach have performance advantages over pure xterm.js implementations?
I've set up an online demo using Wasmer for local execution, so everyone can try easily! (try typing `cowsay hello`):
https://ghostty-web.wasmer.app/
How to try it locally:
npx @ghostty-web/demo@next # The preferred way
# OR
wasmer run wasmer/ghostty-web
-> Go to http://localhost:8080/
Does not appear to work under Firefox, getting a bunch of CORS-related errors (header ‘user-agent’ is not allowed according to header ‘Access-Control-Allow-Headers’ from CORS preflight response) on the /graphql endpoint.
Just fyi, I get no output from "cowsay hello" or "ls", and I see a bunch of errors in the Chrome JS debugger.
Thanks for the feedback! I just pushed a fix, please let me know if you encounter any other issues
Fyi, that online version works for me in Chrome, but not in Firefox (v145.0.2)
Ghostty is so great. Cross-platform but native on Mac and Linux. Core written in a cool random language, showing that you can have well-behaved Mac apps that aren’t just pure Swift / Objective C. Same great design no doubt helps here.
libghostty is stellar! I’m using it for my session persistence for terminal processes tool: https://github.com/neurosnap/zmx
When users reattach to their session we render the terminal state and output from ghostty. Super cool and works really well. It’s basically tmux-lite in 1k LoC
I like that. I don’t want to use tmux (and I don’t when I’m working on my local machine), but I can’t escape it when SSHing. I could ssh to a ton of sessions, but then I 1. Have to remember their names 2. Can’t easily create a new pane (on the remote host) for some short task and 3. Need yet another solution for restoring my pane layout for when my client restarts.
Maybe I’ll try the session name thing, I just foresee it being annoying. Do you see your tool as a shpool replacement?
Yes this completely replaces `shpool`.
I totally understand your concerns for creating new terminals for short tasks. I generally lean towards `nvim` terminal buffers to solve that issue. Or I have a `term` session open that I can quickly go to for random terminal commands that don't belong to a project.
I also (coincidentally) just started using OP's coder, and that also sets up ssh config to use special wildcard hosts, and unfortunately 'hogs' the config (it threatens to trash any changes to the coder section).
Don't give them useful names, just call them 1 or 2 or asdf and let your brain do the mapping.
Love this idea. Though, apparently zig isnt available in any version of Debian including sid, which is annoying. A multiyear packaging effort stalled out 8 months ago with zig 0.14, which is too old for zmx.
Will try this out on my arch system later this week though.
Always love seeing new vt100 implementations! Here's my current pet one running inside Unreal5:
https://imgur.com/a/2vsGS0G
### Photo Log
| Filename | Description |
|----------|-------------|
| ClaudePOV_20251202_134349_2.png | First 720p test - VT100 terminal visible |
| ClaudePOV_20251202_143259_4.png | Inside hyperspace tunnel - green rings |
| ClaudePOV_20251202_143325_5.png | Tunnel with pink/purple shift |
| ClaudePOV_20251202_143432_6.png | BX-2100 silhouette, purple nebula |
| ClaudePOV_20251202_143655_7.png | BX-2100 close-up, cockpit visible |
Can you explain how Claude interacts with the UE Editor? Does it use the Remove Control API through MCP?
I haven't really looked at MCP because it sounds like it is little bit broken?
The Remote Control API is just HTTP/JSON so Claude wrote some powershell scripts to query objects from the endpoint.
We gave Claude a Character Actor in game with an AI controller attached, and it can call functions to the AIController - MovetoXYZ(), Teleport(), TakeScreenshot() etc
Thank you, that's really cool!
The RC API stuff seems a little bit unstable at the moment (parts of it are alpha and beta), but when it works its handy.
nice one kyle! you could add https://github.com/wasmerio/webassembly.sh and have a fully featured in browser shell with support for installing packages!
I'll do this for a much improved demo!
Currently you need the command-line to try it, which is an unfortunate UX.
This is awesome! I'm Syrus, from Wasmer. Would love to help you with this!
We are releasing soon a new version of wasmer-js, so it should be very easy to use it with webassembly.sh (note webassembly.sh and wasmer.sh share the same code)
https://github.com/wasmerio/wasmer-js/tree/main/examples/was...
Neat. I'll take a look. Thanks Syrus!
Everything went smooth (just added a new comment on top of this thread for visibility!), only nit is that `convertEol` didn't work, so I had to manually convert `\n` to `\r\n`.
So, could someone now make a Visual Studio Code (and specifically code-server) that has ghostty-web as the Terminal?
Yup, that's the idea!
How to compile the userspace, though?
Have you seen container2wasm or ktock/vscode-container-wasm?
container2wasm: https://github.com/container2wasm/container2wasm
ktock/vscode-container-wasm: https://github.com/ktock/vscode-container-wasm
ktock/vscode-container-wasm-gcc-example: https://github.com/ktock/vscode-container-wasm-gcc-example
From joelseverin/linux-wasm: https://github.com/joelseverin/linux-wasm :
> Hint: Wasm lacks an MMU, meaning that Linux needs to be built in a NOMMU configuration. Wasm programs thus need to be built using -fPIC/-shared. Alternatively, existing Wasm programs can run together with a proxy that does syscalls towards the kernel. In such a case, each thread that wishes to independently execute syscalls should map to a thread in the proxy. The drawback of such an approach is that memory cannot be mapped and shared between processes. However, from a memory protection standpoint, this property could also be beneficial.
A bit OT here, but oh well
Would hardened_malloc or llvm scudo be useful in a WASM runtime (given that WASM doesn't have an MMU)? https://www.google.com/search?q=would+hardened_malloc+be+use...
Emscripten handles malloc and free with dlmalloc, emmalloc, mimalloc,
emcc your_code.c -s 'MALLOC="emmalloc"' -o your_code.html
"Import custom memory manager?" · Issue #24851 · emscripten-core/emscripten https://github.com/emscripten-core/emscripten/issues/24851
Just learned about Cage:
Cage does Hardware-Accelerated Safe WebAssembly (WASM) with LLVM with support for ARM64 Memory Tagging Extension (MTE) and Pointer Authentication (PAC) memory safety features.
"Cage: Hardware-Accelerated Safe WebAssembly" (2024) https://arxiv.org/abs/2408.11456v2
I made something similar that lets you run TUI applications inside other terminals via ghostty-vt, to implement things like TMUX in opentui
It will be used to render ANSI inside opencode
I'm just here to say coder is great! We love it. Thanks @kylecarbs and the team.
This is super cool! I'm close to releasing a project to make Ink work in the browser for building cross-platform terminal apps. (Ink is what Claude Code / Gemeni CLI use for rendering.)
Currently it uses Xterm.js - but I'll have to try swapping Xterm out for ghostty-web!
I got ghostty-web working with this and it is great. Unfortunately it seems I don't have enough karma to post a link to it. But it's ink-web on npm if you're interested!
The nice thing about this is that you do not need an OS / backend of any kind - everything runs in the browser - similar to webcontainers but without even needing a container.
I love ghostty and I love this
Doesn't trigger keyboard popup on my iPhone in Safari. :(
This may be above my pay grade (does xterm support mobile input?) but I’ll take a look!
Yep! It does
I have no understanding of any of this except that Ghostty is an alternative to iTerm2. Can someone do a ELI5 for the uninitiated?
Ghostty is a terminal like iTerm. This compiles it so it runs in the browser directly, or browser-based environments like VS Code or the Hyper terminal. Without that you’d have to reimplement a whole terminal in JavaScript. Which is what people have been doing with via the xterm.js project. Naturally, there is effort and bugs that go into maintaining a clone/port like that. This lets you use the Ghostty terminal code directly - compiled to WebAssembly and with no other dependencies - as an API-compatible drop-in replacement
That actually pretty much is the ELI5. Its merely a different terminal that offers more features than iTerm2 and also runs on OSX.
Unless you actually need/want those features (which, although I am a terminal aficionado, I must admit are niche as fuck), pick whichever terminal makes you happy. Features that are important to some people are performance, Unicode support, and OS support.
The most decidedly non-ELI5 feature comparison: https://www.jeffquast.com/post/state-of-terminal-emulation-2... and https://ucs-detect.readthedocs.io/results.html
You could argue whether or not it's a "feature", but one of the thing ghostty claims as an advantage is the out of the box configuration.
With no config at all, ghostty looks nicer than my alacritty setup. The rendering is just real nice. I could probably get alacritty to look as nice or nicer, but ghostty just worked this way with no config needed.
So you could consider aesthetics and rendering quality, and simplicity of setup both as features, which people may need/want (or not).
I wouldn't argue against that at all: OOBE is absolutely a feature.
Problem is, we don't all agree with what the OOBE should be. I, for example, always strip out menus, tabs, and other UI features. For me, the terminal that requires the least lines in the config file is probably going to be the winner (assuming no unfixable defects that effect me).
I also have ton of questions. Hopefully the author can add more documentation to ghostty. Right now I don't fully understand the use cases or how people may benefit from ghostty.
This runs in the browser, so it would allow you to connect to a server from your browser and render normal terminal commands in that environment
For instance if you're a cloud provider, and you want people to be able to "drop in a shell" on a machine, but make that available through the web, you could use this
Oh man this is awesome. Recently integrated xterm.js on a new project and was frustrated with the limitations. Great work!
Oh damn, this is awesome.
I wonder if https://github.com/zed-industries/zed/discussions/18129 is still accurate. Would love to be able to use Ghostty as my Zed terminal.
We'd love to (and, tbh, likely will).
Search had been a blocker, but that's coming soon; beyond that not sure that there's any reason other than inertia. Alacritty is totally fine, but excited for the Ghostty focus on performance (obviously), and the font rendering stuff looks excellent (though TBD how much of that we can "just use" vs needing to copy-pasta)
Note search has landed in main, and the core of it is cross platform and exposed via libghostty (Zig API, C to follow).
Woohoo! Thank you!
(Edit) Download it here: https://github.com/ghostty-org/ghostty/releases/tag/tip
i switched from alacritty -> ghostty, and occasionally use zed.
i can't recall why i made the transition (maybe just to try it out, and it became default?). i can't think of any practical consequences of this transition.
why do you care about whether zed uses alacritty or ghostty under the hood?
Kitty Graphics Protocol support and subtle font rendering differences between Ghostty and Alacritty that drive me nuts.
I have reported font rendering issues to Alacritty in the past and let's just say the developer was not exactly receptive to fixing them since they occur on macOS and not his preferred OS of Linux.
I always thought it would be interesting in backend systems to catch a certain exceptions and auto-generate a link to a shell. Given the proper authentication is implemented would this be a good tool to achieve that "remote debug" shell?
Neat. Would be cute to see this in VSCode to replace the terminal there...
can you do a hosted demo with jslinux (or similar) as backend? https://bellard.org/jslinux/
Here's v86 running in your browser with ghostty-web: https://bow-wrinkle-13326.ondis.co/
You can also play around with a real shared containerized machine here: https://ghostty.ondis.co/
This is great. I've been using code-server to embed VSCode into the browser and been missing the terminal functionality. Excited to try this out.
Is there any way for Ghostty to grab all keystrokes? It's a bit of a drag to type ctrl-w inside of Vim, and have the entire browser-tab close ;-)
You could use Firefox and then set the accelerator key to Super, changing all application bindings to use Super instead of Control. This is my setup and it’s great.
I'm curious how you set the accelerator key choice, to Super? Does that let you use function keys inside the Ghostty terminal too?
https://github.com/mozilla-firefox/firefox/blob/FIREFOX_143_...
# Use 17 for Ctrl, 18 for Alt, 91 or 224 for Meta, 0 for none.
- name: ui.key.accelKey
type: uint32_t
#ifdef XP_MACOSX
value: 224
#else
value: 17
#endif
// user.js
user_pref("ui.key.accelKey", 91);I have been looking for this for a while — thank you for making it! I’m gonna explore how I can deploy my BubbleTea TUI’s with it.
Does this version support custom GPU shaders? I have been looking for a command-line with cool-retro-term aesthetics that can run in the browser for a while.
I'd have to let Mitchell answer this accurately.
Considering the native Ghostty does, I _think_ the answer would be yes? I might tinker around with this and let you know.
It's maybe possible. Custom shaders are OpenGL syntax so it'd require transforming them to something compatible with WebGL/WebGPU. In Ghostty GUI we use spire-cross and glslang to transpile shaders at runtime from OpenGL to Metal or OpenGL (with features our host supports).
We'd have to look and see if these support WebGL/GPU. The next problem would be making all that fit into the wasm blob.
Or, we may be able to skip most of this is the OpenGL syntax we use is already compatible. Then no transpiling necessary...
So now let's get ShaderGlass [1] and this to have a baby, so we can have cool-retro-term [2] in the browser.
This is fantastic. Under MIT even! Thank You!
Someone finally figured out how to make it work under Linux!
Not sure I understand :) it's certainly available in nixos https://github.com/NixOS/nixpkgs/blob/nixos-25.11/pkgs/by-na...
Oh it's available, but it only works for about 5 minutes and then it becomes so slow that it's unusable. There was a very long issue about it that was closed with seemingly no effort on behalf of the maintainers.
omg! Seriously, wow. That was quick! Only just heard that Hashimoto libbed out his terminal the other day and remarked about how smart that was... And it made this possible
Do we have Windows support yet?
Not able to enter text on mobile
From "WebAssembly (WASM) arch support for the Linux kernel" (2025) https://news.ycombinator.com/item?id=45784329 :
> JupyterLite still lacks a Terminal e.g. with BusyBox Ash in WASM, with a file system integrated with the Jupyter-xeus kernel file system.
> This [joelseverin/linux-wasm] appears to load much more quickly than other Linux and I think even just bash in WASM demos I've seen.
No hosted demo?
It's tricky to do without a compute environment.
We can easily make a browser shell that let's people run basic commands, but presumably most want to try `vim` and other commands they'd typically invoke.
If you have a Dockerfile that bundles ghostty-web with a backend (even just `ttyd` or a simple socket server), I’d love to host the official demo for you. We can give it a dedicated isolated environment so people can run vim safely.
That would be great!
`npx @ghostty-web/demo@next` starts an HTTP server on `localhost:8080`, so you could just wrap a basic Dockerfile with NPM installed (and maybe a variety of fun Linux tooling, ala vim).
Feel free to shoot me an email: kyle@coder.com. I'll happily add it to the README.
but why?
See the comparison: https://github.com/coder/ghostty-web?tab=readme-ov-file#comp...
Ghostty has much better VT100 compatibility. It should have much better performance as well once we optimize.
The comparison has two points one of which says that for "Complex scripts (Devanagari, Arabic)", ghostty-web has " Proper grapheme handling". But when I tried something extremely simple at the https://ghostty-web.wasmer.app/ or https://ghostty.ondis.co/ demos (just `echo "कवि"`), it failed pretty miserably (and in different ways in the two demos). So I'm not sure what to make of it.
(Seems slightly better in the actual Ghostty app, but not in any usable way: here was my comparison last year https://shreevatsa.net/post/terminal-indic/ and Ghostty is comparable to the other terminal apps, better than some, worse than some. Anyway the fact that it works in Ghostty but not in ghostty-web casts doubt on “Ghostty's emulator is the same battle-tested code that runs the native Ghostty app”. Do you understand what is going on?)