What is Codemode

I'm not sure why almost all codemode implementations choose Javascript. I prototyped an agent[1] to use bash as the language for codemode, which in my opinion worked equally well and requires no teaching (there is literally 0 prompt to teach the LLM about codemode. A tool named "bash" is enough to have them know the usage). [1] https://github.com/ylxdzsw/mu

• searealist · 5 hours ago

  Can do you make a tool or mcp call from bash?

  • clintonb · 5 hours ago

    Yes. Invoking an MCP tool is just an HTTP call. You can do it with curl.

    • searealist · 5 hours ago

      That's one kind of MCP. Another is a local stdio server. Also there are things like subagents, etc (which may be considered tools).

• the_mitsuhiko · 5 hours ago

  > I'm not sure why almost all codemode implementations choose Javascript Because the models are trained on JavaScript for code mode. You get away with way fewer instructions. They also want to be able to express concurrency and that works very well with the Promise global. But a big reason is that code mode runs on the harness side so bash is a tricky target in particular.

  • ylxdzsw · 3 hours ago

    sandboxing is indeed an advantage (can be an important one!), but 1. bash can also express concurrency easily, with sync and async (using standard & syntax) support for each command, and standard cancellation (kill, though crude). 2. "way fewer instructions": It requires no instruction for agents to use bash either, except for merely listing the custom commands (view_image, apply_patch, etc.). Also, bash has standard progressive disclosure mechanism (--help) that models will automatically use with no instruction.

    • the_mitsuhiko · 2 hours ago

      We might be talking past each other here. The point of codemode is to orchestrate the LLM side tool calls, not to orchestrate scripts that it might execute within Bash. In a world where brain and hand are on different machines, getting the bash hands to reach back into the harness brain is something that requires a) putting tools in its hands that it does not know about b) are tricky to set up, usually involving some sort of socket based back channel. I tried this quite a bit, by having pi be always there on the hands side, but it causes a lot of complexity and the LLMs really do not understand it well at all.

• Bonteq · 4 hours ago

  > However bash has one fundamental limitation which is that it can only compose programs that run. And there are some things, which are not programs, but native tools to the LLM and they sort of have to be. The most obvious example here is `read` or `view_image`. If a multimodal model needs to read an image, it cannot use cat for that because the harness needs to inject the actual image payload into the protocol of the LLM. Does your prototype overcome the limitations mentioned in the article?

  • andreypopp · 4 hours ago

    There's no limitation, just have bash commands `read` or `view_image` which communicate back to agent.

    • codybontecou · 4 hours ago

      But doesn't Armin mention the limitation? > If a multimodal model needs to read an image, it cannot use cat for that because the harness needs to inject the actual image payload into the protocol of the LLM. Sorry, I'm just not familiar, but it sounds like there's a protocol the model expects when receiving images that bash does not support? (This is Bonteq, I was just logged into the wrong account.)

      • andreypopp · 4 hours ago

        it cannot use cat but you can make a command which communicates back to agent. Armin mentions that: > While in theory the agent could provide a CLI tool that talks to the outer harness via environment variables and Unix sockets, it’s a rather crude process But I don't know why it's crude to be honest. I'm running pi in tmux and have a CLI to prompt it from any shell session / neovim and it works good. So such way of communication is already needed besides codemode. JS was chosen probably because (1) it's easy to sandbox (there's QuickJS) and (2) (my guess) some models are probably post-trained on JS Codemode.

        • the_mitsuhiko · 3 hours ago

          > But I don't know why it's crude to be honest. I'm running pi in tmux and have a CLI to prompt it from any shell session / neovim and it works good. So such way of communication is already needed besides codemode. It becomes much crummier when hands and brain are on different machines.

          • andreypopp · 3 hours ago

            Agree, but this orthogonal to JS or bash question. (I mean can always run some bash locally as well, even wasm compiled one).

            • the_mitsuhiko · 2 hours ago

              > Agree, but this orthogonal to JS or bash question. It is not from my perspective because Codemode runs in the brain, and bash necessarily runs where the hands are. So if the hands need to reach into the brain, I need to set up a communication layer from the hands to the brain.

  • alfiedotwtf · 2 hours ago

    Surely LLMs understand how to decide base64, but if that’s not possible you could convert the image to ascii and then send that in

• anilgulecha · 4 hours ago

  Almost every model is fully trained on js. That does not need teaching either. Infact harder to sandbox bash (just-bash or brush based) than it is to js or lua, which has fantastic embedded tooling.

Recovery after interrupted execution; distinguishing completed side effects from calls that can safely repeat.

subagents differ: in my claude code logs every subagent cache write is 5-minute tier, main session 1-hour

How is this different to Claude writing mini scripts to get jobs done which it does quite often?

• odo1242 · 4 hours ago

  Claude’s scripts can’t call MCP tools, meaning everything has to be CLIs or libraries. At which point you lose the “everything has self-documenting input-output schema” that Codemode is going for.

  • mi_lk · 33 minutes ago

    > Claude’s scripts can’t call MCP tools Why is that?

I’m still figuring out codemode. I was using it in a prototype, but ended up stripping it out again, after realizing my small local LLM was using more tokens than usual. It was combining tool calls elegantly in code exactly how I hoped it would. The problem was that when any of those embedded tool calls failed (e.g. on parameter validation) the parent code execution tool call also failed. In response, the LLM kept rewriting large parts of the original code block. Btw, Monty by the pydantic team is a joy to work with if you need a way to securely run unverified code. It’s a simplified Python dialect. You can also use it from JS, iirc.

• hamandcheese · 4 hours ago

  This somewhat validates a fear I've had (but hadn't tested) of codemode with smaller models. It works fantastically with Opus and Sol but I've always wondered how well it scales down.

Between this and the Cloudflare post, this is a lot of words and no simple system level picture. Here's what I think is going on: 1. Homoiconicity: Harness mechanics are kludgy and we need proper homoiconicity to uniformly handle code (tool calls) and data ("natural language") as token streams. 2. Actor semantics: for isolation, encapsulation and concurrency. 3. Object capabilities: injected references and no ambient authority. Capabality-based reflection/introspection is a clean way to discover interfaces and affordances. "Code mode" or whatever is basically rediscovering this by hacking outward from LLM token streams, instead of from system design principles based on decades of computer science. It is the beginning of treating an LLM as a programming-language runtime participant (any takers for eval/apply ?) rather than as a text/token generator with the harness as an ad-hoc interpreter. If existing implementations of code mode don't already support all this, I anticipate they will keep piling on hacks till they get to this point. ---- I think it was Dan Ingalls who said "An operating system is a collection of things that don't fit into a language. There shouldn't be one." . I see the same for harnesses -- they're awkward middle children which fit neither in an LLM nor in the programming environment. Maybe the answer is to partner LLMs with Common Lisp or Scheme fibers / Spritely Goblins or Erlang BEAM and be done!

• searealist · 3 hours ago

  It's more like this: Right now when a model wants to call 1 or more tools, there is a fixed json schema to describe the tool calls. Codemode is like: Why don't we just let the model write a program to call the tools and compose them however it wants? The key is that the programming language exposed to do this (usually javascript) will have APIs available to do some things internal to the harness (like call tools/mcp).

• v9v · 2 hours ago

  > Maybe the answer is to partner LLMs with Common Lisp Autolith ( https://autolith.rocks/ ) and some other CL-based harnesses allow the LLM to modify their own harness within the session.

• mi_lk · 1 hour ago

  > no simple system level picture proceed to drop the word homoiconicity... Of course I know what it means without looking up

• nextaccountic · 1 hour ago

  It's actually about context management. Calling a MCP tool will load a potentially huge json on your context window, maybe triggering a compaction. Using a subagent for that is less bad, but still expensive (and you wouldn't run every tool call on a subagent) But if you had a mcp client cli, you can just pipe it to jq or whatever and extract what you need. or chain multiple tool calls into a single one. None of this will make the agent receive the intermediate text passed between those (the agent might want to save the intermediate results into temporary files however) But shell scripting sucks. Javascript or Python is better suited for handling json and things like that. That's what is being called codemode. Ok so.. it makes a lot of sense to integrate agents and programming languages. But right now, harnesses are more or less interchangeable and you can hop to another one very quickly. The more coupling between all those moving parts, the hard will lock-in hit. (just picture the mess that is Claude Code having a severe lock in on the ecosystem)

  • mijoharas · 54 minutes ago

    I agree with most of what you said, but wanted to add that another point is there is a different level of trust in code executing from the harness, and code executing from the bash shell by the agent. I block all network access from bash calls, but want to provide certain tools that can call certain services in a specific way. I can have a tool (or mcp) that does just that, and runs outside of the sandbox.

• lukebuehler · 1 hour ago

  I agree. Harnesses are quickly becoming the next systems programming frontier. The OS analogy is apt and often made--just like browsers have been compared to becoming "platforms" and "OSes". Another analogy that is obvious is threads/processes and agents and sub-agents: all the concurrency, shared resource access, cooperative multitasking, etc problems are emerging again. It will take some time to shake out, but lots of old ideas are new again. Personally, I'm mining lisp machines, homoiconicity, actor models, and other ideas for my harness designs.

• ignoramous · 11 minutes ago

  > Dan Ingalls who said "An operating system is a collection of things that don't fit into a language. There shouldn't be one." Anil Madhavapeddy's take on such setups: A compiler that just refuses to stop. MirageOS is a system written in pure OCaml where not only do common network protocols and file systems and high-level things like web servers and web stacks can all be expressed in OCaml but the compiler just refuses to stop ... compiler, instead of stopping and generating a binary that you then run inside Linux or Windows, will continue to specialize the application that it is compiling and ... emit a full operating system that can just boot by itself. https://signalsandthreads.com/what-is-an-operating-system / https://archive.vn/yLfkq

Can someone please tell me how to disable it permanently in pi? I have already disabled it in settings.json, but, it just doesn't get disabled: { "source": "npm:pi-mcp-adapter", "extensions": [ "-index.ts", "-builtin:codemode" ] } and "autoEnableCodemode": false,

• the_mitsuhiko · 2 hours ago

  MCP or codemode do not enable automatically, so not sure why they enable in the first place for you. Ask pi to figure out why it's one :) { "extensions": ["-builtin:codemode"] } Is all that is needed to turn off codemode entirely. And -builtin:mcp would independently get completely rid of mcp.

I've noticed that code mode seems to cause progressive lobotomisation in Sol 6.1 around subagents. The more it uses it, the worse it gets at giving prompts to subagents: URLs, datasourceproxy accesspathonlyallowed anddefault404. Do not set authbasic onprivate ports; perplanPodmannetwork trustedinfrastructure nottenant boundary. Publicroutes internal /tinyauth protected internal, proxyGETemptybody /api/auth/nginx toprivate tinyauth3000; proxy_pass_request_headersoff, CookieonlyTinyauthSession header extracted map name/value actual runtime pattern tinyauth-session-[0-9a-f]{8}, X-Original-URL constructed This is unedited; it's merging words together and spamming keywords.

So... What exactly is it in the end? I try to parse the long prose, and couldn't. It doesn't help that the article is titled "What is Codemode" and then goes to say "If you are not familiar with Codemode, it’s basically just...". You article is supposed to say what it is without anyone being familiar with it. Like what does this passage even mean: --- start quote --- For instance if you issue a bash call as a regular tool call in the LLM, then we only throw the trailing 2000 lines into the context and if the agent wants more, it needs to look at the overflow file itself. If however the agent issues that invocation via Codemode, then the Codemode side gets larger outputs sent structurally. --- end quote ---

• lpedrosa · 3 hours ago

  Unfortunately if you're not in the deep end when it comes to these tools, your brain will only be able to parse gibberish. I was expecting a bit more care from Armin in explaining what does codemode actually do, from first principles.

  • the_mitsuhiko · 1 hour ago

    Well that was my best attempt so far. I have to say that I find it quite tricky to convey.

• the_mitsuhiko · 1 hour ago

  > Like what does this passage even mean: It means that a LLM side tool (bash) can expose larger (and structured) outputs to Codemode than it normally does when that tool is executed straight to the LLM back as text.

• sqwxl · 1 hour ago

  i was also confused. this introductory post by the creators of Codemode is much easier to follow: https://blog.cloudflare.com/code-mode/

Why is this a personal blog, not a Pi post? https://earendil.com/posts/you-said-no-mcp/ remains difficult to read without understanding what codemode is, with some quote like "Now we talked so much about Codemode, it might be worth explaining what that even is."

Sadly this seems like introducing a very complex apparatus for little gain. I don't need MCP or many tool calls that the agent can program around - in fact the promise of pi was that you basically just need bash and no other tools. The minimally-invasive approach would have been to just "inject" tool calls as virtual bash commands. No code mode required, no hands vs. brains dichotomy. LLM can use language of its own choosing to interact with tools.

Am I crazy for saying I like codemode? It reduces the amount of turns by about an order of magnitude.

• mijoharas · 50 minutes ago

  not at all, it's nice! solves the composability problem while keeping a trust separation between harness/ai bash calls.