Birbla

Join the discussion

Write your take first — we'll ask for email only when you're ready to publish.

Sign in
  • Hacker News
  • To me, Before agentic programming a harness was like a mini framework in the app. Like for testing mostly. You’d set up the harness and configure it for your test and it would take care of boilerplate setup / optional reporting / benchmarks ect. Still works for both - but yea need a new word I guess
    by stacktraceyo
  • From a naming terms yes, the closest equivalent of the past is the term "framework". Having written a Go service framework that's how I perceived it and as I started to work on agents, anything related to that became an "agent harness". I guess naming and terms change with different paradigms.
    by asim
  • My 2c. A lot of what’s being discussed here may boil down to experience (or lack thereof) of writing good functional (and non-functional) requirements. Some developers are always thinking about implementation (or at least, implementation approach), and as a result they are very technically prescriptive. There’s nothing wrong with that per se if you’re actively driving towards a specific architecture (for your own reasons - which could be specified as non-functional reqs).

    What others are describing is the BA skill of capturing good _business_ requirements ie. specifying outcomes and qualities rather than methods.

    We should be clear about who’s being the BA, the architect and the developer here. At one end, a human vibe coder is acting as BA and the AI as architect, designer and engineer. At the other end, the human is a senior dev closely instructing a AI junior dev. All approaches are valid depending on what you need and the AI tools available (eg. SOTA model vs small self-hosted open-weights model).

    by phs318u
  • A harness is "the code that gives a model an operational environment" according the the framing in https://github.com/shareAI-lab/learn-claude-code -- which is a build your own python claude code tutorial shareAI made after the code leak a few months back.
    by tingletech
  • I think a harness is kind of anything around the intelligence that allows the intelligence to be applied towards something, some sort of task. A great (if off-color) example I remember hearing was how Steven Hawking was brilliant, but really needed that computer setup to be able to apply his intelligence. It really stands out to me as such a clear visual example of what a harness actually is.

    Anyway I've been building my own harness on top of pi- www.freepi.ai (it's based on Pi, but now I have an OpenAI compatible endpoint so I'm thinking of it more like free-api :-) ). Basically ad+training supported so I can offer completely free inference. It's really important to me that we don't have harnesses and intelligence trapped in a "have and have not" world. If we don't all have access to intelligence we will end up in a dark place.

    Thats again where the visual of Steven Hawking and the wheelchair really stand out in my mind. It's not enough to have the raw intelligence, we need a really good wheelchair too.

    by freepiai
  • i also like the backpack analogy

    the harness is what you take with you on a trip/task

    whatever you take with you is not free (system prompt, tools, skills …)

    some models are really good even if you bring almost no skills, tools or system prompt

    the harness is the complement to the model

    the better the model the more minimal the harness can be

    harnesses like pi [0] and smol [1]are on the more minimal end of things

    [0] https://github.com/earendil-works/pi

    [1] https://github.com/smol-env/smol

    by tosh
  • Not a bad analogy because the bigger your backpack the slower you walk. With models a big context and tool set degrades performance. So you want the smallest harness/backpack that can do the job.
    by lebek
  • Clear, relevant, and easy to understand. Thank you for writing this up, I’ll be sharing this link with all my non-tech friends!
    by childofhedgehog
  • Author here. Thanks - I appreciate the feedback
    by ni10c
  • I second that. Not using agents myself but trying to get an idea on how this stuff works, so I always wondered what an "harness" even is, since anyone seems to assume that this is common knowledge. Now it is really clear to me!
    by phforms
  • A harness is a tool that allows the LLM to focus on the primary objective that the user wants, coding, research, reports, finance anything really but the harness structures the agent interactions with the supporting tools to achieve the narrow scope. Driving the LLM with correct feedback from the domain knowledge provided by the tools. TBH when I was writing my harness this is why i have the Guardrails concept around Any tool, pre and post tool call, pre can make sure the data is formatted correctly lowering incorrect tool calls and post tool calls for validaition of results of output. Harness: https://github.com/zarldev/zarlmono/tree/main/zarlcode Guardrail Design: https://zarldev.github.io/zarlmono/guardrails/ All Docs: https://zarldev.github.io/zarlmono/
    by zarldev
  • The ai hype word for 2026 after agent in 2025 for any LLM powered application.

    Well kind of, I wouldn't be surprised to see that some things marketed as agents are actually good old deterministic software.

    by jascha_eng
  • My guess is that everything "reliable" in LLM/agentic-coding comes down to either calls to reliable/deterministic tools or providing well-defined success criteria (such as loads of unit tests) for the LLM to throw its stuff at in "agentic loops" until something sticks.
    by phforms
  • It's really funny (and a bit obnoxious) to watch the vocabulary from the outside. In 2023 everybody learned the word moat, then it's been agent(ic), from last year there's more talking about harnesses than at a bungee jumping convention. The mot du jour is frontier.

    It truly proves like there's a handful of thought leaders on Twitter that everybody follows blindly and start to copy down to the lexicon and parrot everywhere else.

    by sph
  • Author here. It’s ironic because this post was clearly geared towards non-hackers. But now that we’re here.. the other analogy I considered presenting was:

    harness = chassis, model = engine, fuel = tokens, agent = car

    I’m curious what y’all might think and whether that analogy carries more explanatory power

    by ni10c
  • I actually use the computer as a metaphor. The LLM is the CPU. The harness is the motherboard which controls communication between the CPU and other components like memory, hardrive, and inputs. In other words, how the LLM interacts with the outside world, and outside world with the LLM.

    I've been building coding harnesses since 2021 and believed in their value for a long time. Harnesses matter a lot, look at what claude did for Anthropic.

    by mempko
  • I'm a climber so I'm biased but I really liked your climbing harness example because of the configuration you're able to easily make to the harness.

    Saying the harness is like a car's chassis doesn't work as well for me because the chassis isn't as configurable as a climbing harness for as little work.

    Getting deeper into the climbing analogy you can even swap out the harnesses themselves for wildly different climbs. Like using Claude Code with a bunch of agents for medical software (climbing K2 where that extra padding comes in super handy) and pi.dev with a local model for a respectable web project (sport route where you'll be back in a few hours and it's safe to be a little more exposed).

    I'm glad your article made HN, and thank you for pi!

    by troyvit
  • The first analogy that comes to mind, growing out of "harness", is more like harness = harness, model = horse (rather than harness as in climbing harness).

    I guess you could say that tokens = hay, and agent = horse and cart, from there? Not sure how useful the hay part is but you could observe from the second that there are many different things you could harness a horse to (also a plough, or a coach, or just a saddle) based on your goal.

    by asQuirreL
  • Harnesses are the next frontier. If LLMs are electricity, harnesses are the “electronics.” Right now, it’s like an AC vs DC between Claude and ChatGPT, but once that settles, the harnesses will be the actual value providers.

    And Pi is the best harness because of the amazing extension system. You can build extensions that turn Pi into a stock trader, software factory, anything. I tried switching to another harness but none have extension functionality as good as Pi.

    Even if there is a new harness or agent project, I tell Pi to dig into the codebase and then make me an extension that brings that functionality into Pi. I did it with Prime Intellect’s and Deepseek’s harnesses and those are built on Pi.

    by theturtletalks
  • This is a plug, but relevant. I recently added a 'build native tools on the fly' functionality to Dirac (https://github.com/dirac-run/dirac) that works like:

    1. You can use the '/new-tool' and tell what kind of tool you want (including whether it should be task-scoped, workspace-scoped, or global), the model builds it, the harness runs validation and other tests until the tool is ready

    2. The model decides that in such and such task, it would be helpful to have a tool like this, it can build a task-scoped tool.

    In either scenario, the tool catalog is rebuilt, and the new tool is instantly available in the next turn.

    by GodelNumbering
  • I've been getting a little frustrated with having to rearchitect things any time I want to try a new harness. Wrote about my most recent experiments with separating conversation from control loop here and using MCP as the seam here: https://demianbrecht.com/posts/the-harness-within-the-harnes.... This allows me to build a spectrum of agentic to entirely deterministic tools and be able to port them from one harness to another with only a minimal amount of harness-specific config.
    by dbrecht_
  • Pi's most popular extensions, by download count:

    https://pi.dev/packages?type=extension

    by timbowhite
  • If LLMs are oxen, harnesses are... the harnesses
    by Aardwolf
  • I've never used Pi but I don't see why you can't use stock codex or claude code for the same purpose, what makes Pi special? I've built plenty of custom harnesses on top of claude code and codex using custom skills or simple markdown instructions and subagents. Never had any issues or limitations with that approach.

    I do agree that harnesses are going to extend AI capabilities a lot in the next year, but after reading Pi's page I don't see anything that makes it particularly special in terms of functionality, other than being more provider-agnostic.

    by jrflo
  • > ...once that settles, the harnesses will be the actual value providers.

    The words "once that settles" are doing historic levels of work here.

    No human on earth has a clear idea whether model technology will settle tomorrow or 100 years from now.

    There's every reason to expect architectural breakthroughs will keep being discovered and causing nuclear blasts of forward progress.

    by jacobgold
  • > Harnesses are the next frontier. If LLMs are electricity, harnesses are the “electronics.”

    I really though this comment was a satire ...

    by mpawelski
  • > If LLMs are electricity, harnesses are the “electronics.” (...) the harnesses will be the actual value providers.

    Don't get ahead of yourself. Harnesses are not exactly rocket science and will be a commodity.

    The real value providers here are the hardware, then the LLM as a distant second, and at a much larger distance the harness.

    by amelius
  • Does anyone have a suggestion for a harness that is good at handoff?

    When I say handoff, I mean:

      * handoff from a terminal CLI to webui (on a phone)? 
  * handoff from one team member, to another?
  * handoff from one communication modality, like writing a prompt in a TUI, to email? 
  * handoff from one model to another, or one provider (openrouter)( to another (llama.cpp)
    Does such a thing exist?

    I used to think that a PR would be a good place to centralize all this. Who cares what IDE, or developer, or location. But, now I feel like an agent harness might contain that better.

    Why do I want handoff? I keep losing context of where my harness is running. Sometimes I am inside an isolated VM. Sometimes I'm on my laptop, sometimes I'm on my home machine with the big GPU for local models. If I could spin up a harness that could identify itself inside my tailscale network, then I could probably have a single web UI which allows me to keep all that context straight.

    I'm tempted to experiment with Pi to configure such a thing. But, perhaps there are patterns out there already with a harness I have not considered.

    by xrd
  • Not really solving all your cases, but I found tmux (or herdr) on a home server works pretty well. I just ssh into my home server and continue where I left off with the same claude/opencode open.

    On a longer term, I think "assistant" style harnesses might help here, like vellum.ai. I no longer use that, but I asked it to create an ACP proxy through iroh (basically tailscale but on the application layer), and it managed to control claude on another device of mine. A friend did similar stuff with tailscale.

    I have started writing a hobby harness with a web interface where I would like to support this "ACP proxy" mode natively, and also to make the models aware of different devices in some way and "move" work between them.

    by gf000
  • Hermes has /handoff to go from cli or desktop to IM, possibly other ways.
    by speed_spread