fx :Tiny, open, native coding agent.

hankbond

Will dive in later to see how its contribution/extension model differs from Pi. Pi is great for a lot of things but has a larger memory footprint and start time than this claims to have so it would be interesting to compare the two.

rvz

Some questions: 1. Why do we need yet another coding agent over the rest of them? 2. Is this going to be another Vercel Labs slop project that they will abandon like the others since this is super experimental?

jauntywundrkind

Is Vercel so all-in on Zig elsewhere too?

SmashDan

I'm not in the tech industry. Could someone explain why there are so many new coding agents, and why they're commonly upvoted on HackerNews? It seems like there's a new one in the top 10 every other day.

rsyring

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.

sixtyj

I don’t want another coding agent. I would have to be unemployed to try all new software that pops up everywhere. :) And every says it is the one :)

konaraddi

Nice to see herdr support. The docs seem to imply it only works with vercel’s AI gateway? I guess it cant be configured to use another provider?

vhantz

I wonder how long will the "curl my arbitrary script and pipe it to bash" will continue being a delivery method.

smy20011

I was wondering to build the same thing but someone already built it. I just need some agent that open/close super fast and don't eat half a gb of memory.

kgeist

>Tiny ~6mb binary I wonder why it's so large for a program written in Zig. It's basically just a loop that accepts user input, prepares the context, sends it to the LLM, parses the output, invokes the tools, and presents it all in the terminal. Add the built-in prompts and a few checks here and there (like blocking a write tool call before the file has been read first), and I'd expect a truly tiny native agent to be around 200-300 KB max.

fazxes

fx isn’t primarily “another coding agent.” It’s a tiny, embeddable agent harness and infrastructure component that also happens to have a good CLI.

impulser_

I'm sorry, but this is pure slop. This has 26 tools and a tool for every single file operation and a tool for read tool output? What the fuck... And they call this minimalist.... Lmfao The person who built this obviously has little understanding of harnesses. You should have significantly less tools today with how good LLMs have become. The start up time and binary size are quite literally the most useless stats to base a harness off of lol Man what with Cloudflare, Vercel and all these tech companies just releasing pure slop. Just use Pi. It's actually minimal and well thought out by people who actually understand agents.

bodge5000

It does looks really interesting and definitely something I'll check out, but (genuine question), should "agent" and "agent harness" be used interchangeably as it is on here? It describes itself as an agent harness, but the tagline is "tiny, open, native coding agent". I'm not sure harness is the right word either, but that seems to be what the industry has settled on so I'll concede on that, but surely the agent is the thing doing the work (which I guess is the model, or an instance of the model which is why agent is different?), whereas the harness is how the user interacts with the agent. We've had ways to describe that relationship before; client and server, frontend and backend, but again, I'll concede that the shiny new thing doesn't want to use boring old terminology, but I think some consistency and logic in the shiny new terminology is pretty important That isn't specifically about fx of course, more of a general industry complaint

alexboehm

I too was frustrated with needing npm and slow startups or huge rust compile times for agents. I tried getting agents to write a tool like this with proper raw mode content pasting/ interruptions, but they just kept screwing it up without a framework like ratatui, so I wrote one in c by hand https://gist.github.com/fourlexboehm/a60e4ef9306744483731cd1... the only dependency is libcurl. This binary is ~40kb and uses much less ram than fx.