5 ms·

For all the people asking "Why?", it seems like TFA has a pretty good list of features/attributes that it thinks sets it apart: - fx is a coding agent harness

by rsyring 29d ago

For all the people asking "Why?", it seems like TFA has a pretty good list of features/attributes that it thinks sets it apart: - fx is a coding agent harness and CLI written in Zig, optimized for research and embeddability as part of larger systems. - It focuses on minimalism and performance across the board, from system prompt design, to its tools, feature set, and 6.39mib binary. - For end users, its CLI output style and form factor aims to be closer to a Unix shell than a heavy "IDE in the terminal" TUI. - It's open source (Apache-2.0), model-agnostic, and suitable for both local and cloud inference. - Designed for instant installation and embedding in resource constrained environments and agent sandboxes. - fx cold starts in 10µs and does no unnecessary work or I/O prior to accepting user input, making it ideal for programmatic use. - Optimal fx.wasm builds produced by the Zig toolchain, which further reduce fx's size, making the network stack pluggable. - fx contributes single-digit megabytes of memory baseline, allowing you to pack many instances in one machine. - fx preserves scroll history by default, produces minimal output, and makes sparing use of complex TUI or paints - Minimal system prompt and tools, to save on token costs and to yield optimal time-to-first-token performance (TTFT). - Small core, extended via skills, plugins, MCPs, with a Unix-like philosophy to extensibility. - Designed to work with local models, gateways, direct provider API access or subscriptions.

Kim_Bruning 29d ago
Very neat. The demo on the page feels very intuitive to me! (if you're used to bash at least)
rvz 29d ago
Most of all what you have said is not really any clear differentiation against the rest of the 100s of other agents. Just minuscule or non-negligible implementation details and I'm afraid it is sadly yet another experimental slop project. It is a branded "mee too" coding agent that we have seen hundreds of them already.
- rsyring 29d ago
  I can't say I'm super into all the agents that are being created. But I do try to keep up here on HN and I can't say that I can remember any with this particular set of attributes. In particular, aiming to be embeddable into other projects seems rather notable. At least, not something I've remembered of other projects that have made there way across the HN front page.
  - qudat 29d ago
    Pi is a composition of libraries that can be used to build agents. That seems far more interesting than this “minimal” agent. This was written in zig and built by vercel. That’s the only notable characteristics about this project. All code agents look the same and this one is no different.
    - slowin 28d ago
      I don't think Pi is tiny because it's written in typescript and requires a javascript runtime. I definitely want a "tiny" compiled agent with no runtime requirements. I don't think Zig is that great of a language for this, but it's better than typescript. I don't want to use Vercel software so will pass, but would love to see a more community driven effort.
      - kalms 28d ago
        What’s a better lang in your opinion?
        rurban 27d ago
        Go or Rust or C++
      - sieste 27d ago
        For people working with small local models like Qwen 35b what's even more important us that the LLM is good at coding in the language in which the agent harness is written so that it can write skills. I really like pi but had a few instances now where Qwen wasn't able to extend it because it isn't very good at writing typescript. Does that sound familiar to anyone, and did you find any fixes?
cmrdporcupine 29d ago
"- For end users, its CLI output style and form factor aims to be closer to a Unix shell than a heavy "IDE in the terminal" TUI." I've actually been wondering lately why coding agent functionality isn't just... part of my shell already. Just another kind of interaction modality with an existing shell. Could probably even be an extension to fish or nu-shell even. Please stop me from forking off on yet another project though.
- rsyring 29d ago
  Originally, Warp was doing just that. Reimagining the terminal including making AI a part of it. I don't think they really found much purchase there because they ended up needing to make a platform out of it: https://www.warp.dev/ https://www.warp.dev/
  - cmrdporcupine 29d ago
    Yeah terminal window is a bit of a different story, though. I mean the actual shell binary. With some ... intensive ... security/sandboxing/containerizing of some kind though, I guess.
- pjmlp 28d ago
  Microsoft has you covered, https://devblogs.microsoft.com/commandline/intelligent-terminal-0-2-is-here-with-local-model-support/ https://devblogs.microsoft.com/commandline/intelligent-termi... https://devblogs.microsoft.com/commandline/github-copilot-in-windows-terminal/ https://devblogs.microsoft.com/commandline/github-copilot-in...
jauntywundrkind 29d ago
I've only done a little of the new opencode v2 "mini" but it too offers a nice preserve-scroll by default. OpenCode is the best behaved TUI i've seen by far (they invented OpenTUI to make it so good, also in Zig), so it feels less crucial. But it's nice to have there! The "small core" model is very popular all of a sudden. DeepSeek's new harness is famously like that. https://news.ycombinator.com/item?id=49285244 https://news.ycombinator.com/item?id=49285244 OpenCode isn't quite as small, but there's very much been a deliberate attempt to drive much more into a plugin-based system. I enjoyed Dax talking about the new constitution of opencode, and the results of his agent comparing OpenCode & the new DeepSeek. https://bsky.app/profile/thdxr.com/post/3msy4gjttoc2f https://bsky.app/profile/thdxr.com/post/3msy4gjttoc2f https://bsky.app/profile/thdxr.com/post/3msygiqyg6v2y https://bsky.app/profile/thdxr.com/post/3msygiqyg6v2y > an architectural change we made in opencode2 is nearly everything is an internal plugin / there's 68 of them that cover our built in agents, integrations, config loading, etc i also think this is such a brilliant fun architectural twist too: > OpenCode is the first time i could justify event sourcing in a real system / everything that happens is an event which gets projected into the sqlite db https://bsky.app/profile/thdxr.com/post/3mt2qx3ktib2c https://bsky.app/profile/thdxr.com/post/3mt2qx3ktib2c it's so fun seeing new malleable software cores emerge, try to figure out how to augment agency. agentic software striving itself to extend the agency it itself offers. it's been way too long since we've had ambitions to build general system, architectures that serve more than the user. this has held computing back for far too long. this is such an excellent interesting field, of such a more ambitious computing, opening up.
- solarkraft 29d ago
  Thanks for the links on opencode 2! I’ve been meaning to get into this as I’ve been frustrated about some opencode 1’s behavior and design. Many of the encounters made me come up with ideas I’m happy to see they also had! As much fun as it may have been to build my own harness, I feel like the core primitives should be pretty well understood by now (in fact I envision a standard core library / API design taking shape).
- rurban 27d ago
  This sound exactly like the new DeepSeek Harness cli. But I switched to oh-my-pi and crof.ai recently (cheap deepseek). Behaves better than opencode, and I love their /collab remote control.
OleksandrC 28d ago
If you like this list of "why?", you might also like this: https://usehax.dev/ https://usehax.dev/ (I am the author). Most of the list applies, similar minimalist Unix tool approach, with some differences. Hax is written in C, the dynamically linked binary is even smaller (0.6 MB), MIT-licensed. No wasm though. Important difference - fx is currently Vercel AI Gateway only - while hax does support multiple providers already (OpenAI API, ChatGPT/Codex subscription, Anthropic API, OpenRouter, OpenCode Zen/Go), and integrates well out of the box with local llama-server.
- rgbrgb 28d ago
  this looks great! what are you using it for? i like the idea of being able to use one of these (sandboxed) within a larger program kind of like how I use LLM's to do small tasks within my apps now but with a few tools (web search). my current way of doing that is like building a mini-harness with a couple tools within the app, but something more drop-in would be better obviously.
  - gandreani 28d ago
    I was going to ask if there's any plans to integrate something like the fx's ACP server[1] or pi's RPC mode [2]. I'm making something like Paseo and hax is very interesting as a Pi replacement. [1] https://fx.sh/docs/using-fx/acp https://fx.sh/docs/using-fx/acp [2] https://pi.dev/docs/latest/rpc https://pi.dev/docs/latest/rpc
- tecoholic 28d ago
  It’s funny what “tiny” means for different people depending on their background. I expected it to be under an MB as well and was surprised by 6MB.
  - nine_k 28d ago
    A typical Go binary would be 2-3 times larger. A typical Node project would easily pull more than 6 MiB of just code, not counting the runtime.
  - 28d ago
verdverm 28d ago
Does it have anything co-designed around Vercel infrastructure? This is what happened to NextJS and why I will likely never touch Vercel open source again
- rafael-lua 28d ago
  Yeah, I see the Vercel logo, and I am instantly out.
  - NamlchakKhandro 23d ago
    and like Barbara, i'm out.

by rsyring 29d ago

Kim_Bruning 29d ago

Very neat. The demo on the page feels very intuitive to me! (if you're used to bash at least)

rvz 29d ago

Most of all what you have said is not really any clear differentiation against the rest of the 100s of other agents. Just minuscule or non-negligible implementation details and I'm afraid it is sadly yet another experimental slop project. It is a branded "mee too" coding agent that we have seen hundreds of them already.

rsyring 29d ago
I can't say I'm super into all the agents that are being created. But I do try to keep up here on HN and I can't say that I can remember any with this particular set of attributes. In particular, aiming to be embeddable into other projects seems rather notable. At least, not something I've remembered of other projects that have made there way across the HN front page.
- qudat 29d ago
  Pi is a composition of libraries that can be used to build agents. That seems far more interesting than this “minimal” agent. This was written in zig and built by vercel. That’s the only notable characteristics about this project. All code agents look the same and this one is no different.
  - slowin 28d ago
    I don't think Pi is tiny because it's written in typescript and requires a javascript runtime. I definitely want a "tiny" compiled agent with no runtime requirements. I don't think Zig is that great of a language for this, but it's better than typescript. I don't want to use Vercel software so will pass, but would love to see a more community driven effort.
    - kalms 28d ago
      What’s a better lang in your opinion?
      - rurban 27d ago
        Go or Rust or C++
    - sieste 27d ago
      For people working with small local models like Qwen 35b what's even more important us that the LLM is good at coding in the language in which the agent harness is written so that it can write skills. I really like pi but had a few instances now where Qwen wasn't able to extend it because it isn't very good at writing typescript. Does that sound familiar to anyone, and did you find any fixes?

cmrdporcupine 29d ago

"- For end users, its CLI output style and form factor aims to be closer to a Unix shell than a heavy "IDE in the terminal" TUI." I've actually been wondering lately why coding agent functionality isn't just... part of my shell already. Just another kind of interaction modality with an existing shell. Could probably even be an extension to fish or nu-shell even. Please stop me from forking off on yet another project though.

rsyring 29d ago
Originally, Warp was doing just that. Reimagining the terminal including making AI a part of it. I don't think they really found much purchase there because they ended up needing to make a platform out of it: https://www.warp.dev/ https://www.warp.dev/
- cmrdporcupine 29d ago
  Yeah terminal window is a bit of a different story, though. I mean the actual shell binary. With some ... intensive ... security/sandboxing/containerizing of some kind though, I guess.
pjmlp 28d ago
Microsoft has you covered, https://devblogs.microsoft.com/commandline/intelligent-terminal-0-2-is-here-with-local-model-support/ https://devblogs.microsoft.com/commandline/intelligent-termi... https://devblogs.microsoft.com/commandline/github-copilot-in-windows-terminal/ https://devblogs.microsoft.com/commandline/github-copilot-in...

jauntywundrkind 29d ago

I've only done a little of the new opencode v2 "mini" but it too offers a nice preserve-scroll by default. OpenCode is the best behaved TUI i've seen by far (they invented OpenTUI to make it so good, also in Zig), so it feels less crucial. But it's nice to have there! The "small core" model is very popular all of a sudden. DeepSeek's new harness is famously like that. https://news.ycombinator.com/item?id=49285244 https://news.ycombinator.com/item?id=49285244 OpenCode isn't quite as small, but there's very much been a deliberate attempt to drive much more into a plugin-based system. I enjoyed Dax talking about the new constitution of opencode, and the results of his agent comparing OpenCode & the new DeepSeek. https://bsky.app/profile/thdxr.com/post/3msy4gjttoc2f https://bsky.app/profile/thdxr.com/post/3msy4gjttoc2f https://bsky.app/profile/thdxr.com/post/3msygiqyg6v2y https://bsky.app/profile/thdxr.com/post/3msygiqyg6v2y > an architectural change we made in opencode2 is nearly everything is an internal plugin / there's 68 of them that cover our built in agents, integrations, config loading, etc i also think this is such a brilliant fun architectural twist too: > OpenCode is the first time i could justify event sourcing in a real system / everything that happens is an event which gets projected into the sqlite db https://bsky.app/profile/thdxr.com/post/3mt2qx3ktib2c https://bsky.app/profile/thdxr.com/post/3mt2qx3ktib2c it's so fun seeing new malleable software cores emerge, try to figure out how to augment agency. agentic software striving itself to extend the agency it itself offers. it's been way too long since we've had ambitions to build general system, architectures that serve more than the user. this has held computing back for far too long. this is such an excellent interesting field, of such a more ambitious computing, opening up.

solarkraft 29d ago
Thanks for the links on opencode 2! I’ve been meaning to get into this as I’ve been frustrated about some opencode 1’s behavior and design. Many of the encounters made me come up with ideas I’m happy to see they also had! As much fun as it may have been to build my own harness, I feel like the core primitives should be pretty well understood by now (in fact I envision a standard core library / API design taking shape).
rurban 27d ago
This sound exactly like the new DeepSeek Harness cli. But I switched to oh-my-pi and crof.ai recently (cheap deepseek). Behaves better than opencode, and I love their /collab remote control.

OleksandrC 28d ago

If you like this list of "why?", you might also like this: https://usehax.dev/ https://usehax.dev/ (I am the author). Most of the list applies, similar minimalist Unix tool approach, with some differences. Hax is written in C, the dynamically linked binary is even smaller (0.6 MB), MIT-licensed. No wasm though. Important difference - fx is currently Vercel AI Gateway only - while hax does support multiple providers already (OpenAI API, ChatGPT/Codex subscription, Anthropic API, OpenRouter, OpenCode Zen/Go), and integrates well out of the box with local llama-server.

rgbrgb 28d ago
this looks great! what are you using it for? i like the idea of being able to use one of these (sandboxed) within a larger program kind of like how I use LLM's to do small tasks within my apps now but with a few tools (web search). my current way of doing that is like building a mini-harness with a couple tools within the app, but something more drop-in would be better obviously.
- gandreani 28d ago
  I was going to ask if there's any plans to integrate something like the fx's ACP server[1] or pi's RPC mode [2]. I'm making something like Paseo and hax is very interesting as a Pi replacement. [1] https://fx.sh/docs/using-fx/acp https://fx.sh/docs/using-fx/acp [2] https://pi.dev/docs/latest/rpc https://pi.dev/docs/latest/rpc
tecoholic 28d ago
It’s funny what “tiny” means for different people depending on their background. I expected it to be under an MB as well and was surprised by 6MB.
- nine_k 28d ago
  A typical Go binary would be 2-3 times larger. A typical Node project would easily pull more than 6 MiB of just code, not counting the runtime.
- 28d ago

verdverm 28d ago

Does it have anything co-designed around Vercel infrastructure? This is what happened to NextJS and why I will likely never touch Vercel open source again

rafael-lua 28d ago
Yeah, I see the Vercel logo, and I am instantly out.
- NamlchakKhandro 23d ago
  and like Barbara, i'm out.