I disagree with this section about WebAssembly:

> But the practical limitation is language support. You cannot run arbitrary Python scripts in WASM today without compiling the Python interpreter itself to WASM along with all its C extensions. For sandboxing arbitrary code in arbitrary languages, WASM is not yet viable.

There are several versions of the Python interpreter that are compiled to WASM already - Pyodide has one, and WASM is a "Tier 2" supported target for CPython: https://peps.python.org/pep-0011/#tier-2 - unofficial builds here: https://github.com/brettcannon/cpython-wasi-build/releases

Likewise I've experimented with running various JavaScript interpreters compiled to WASM, the most popular of those is probably QuickJS. Here's one of my many demos: https://tools.simonwillison.net/quickjs (I have one for MicroQuickJS too https://tools.simonwillison.net/microquickjs )

So don't rule out WASM as a target for running non-compiled languages, it can work pretty well!

• syrusakbary

  today at 8:46 PM

  I also disagree with that.

  Wasmer can run now Python server-side without any restrictions (including gevent, SQLAlchemy and native modules!) [1] [2]

  Also, cool things are coming on the JS land running on Wasmer :)

  [1] https://wasmer.io/posts/greenlet-support-python-wasm

  [2] https://wasmer.io/posts/python-on-the-edge-powered-by-webass...

  • shayonj

    today at 8:49 PM

    Wasmer looks v cool. I must check it out

• shayonj

  today at 8:42 PM

  That is a good call out and I missed to consider the options you pointed. When I am back on keyboard I will add an updated note with a link to your comment. Thank you!

OK, let’s survey how everybody is sandboxing their AI coding agents in early 2026.

What I’ve seen suggests the most common answers are (a) “containers” and (b) “YOLO!” (maybe adding, “Please play nice, agent.”).

One approach that I’m about to try is Sandvault [0] (macOS only), which uses the good old Unix user system together with some added precautions. Basically, give an agent its own unprivileged user account and interact with it via sudo, SSH, and shared directories.

0. https://github.com/webcoyote/sandvault

• stephen_cagle

  today at 10:26 PM

  I use KVM/QEMU on Linux. I have a set of scripts that I use to create a new directory with a VM project and that also installs a debian image for the VM. I have an ./pull_from_vm and ./push_to_vm that I use to pull and push the git code to and from the vm. As well as a ./claude to start claude on the vm and a ./emacs to initialize and start emacs on the vm after syncing my local .spacemacs directory to the vm (I like this because of customized emacs muscle memory and because I worry that emacs can execute arbitrary code if I use it to ssh to the VM client from my host).

  I try not to run LLM's directly on my own host. The only exception I have is that I do use https://github.com/karthink/gptel on my own machine, because it is just too damn useful. I hope I don't self own myself with that someday.

• stefans

  today at 9:14 PM

  Looked into Apples container framework first (for proper isolation) but switched to Docker sandboxes since they switched to mircoVMs too: https://docs.docker.com/ai/sandboxes/#why-use-docker-sandbox...

  • jbverschoor

    today at 9:45 PM

    Quite similar to how Im using docker for a few years

    https://github.com/jrz/container-shell

• scosman

  today at 9:59 PM

  Shell over MCP, with multiple options for sandbox. Includes Docker, Podman, Modal, E2B, and WASM:

  https://github.com/Kiln-AI/Kilntainers

  Can run anything from a busybox in WASM to a full cloud VM. Agent just sees a shell.

• simonw

  today at 8:54 PM

  I'm mainly addressing sandboxing by running stuff in Claude Code for web, at which point it's Anthropic's problem if they have a sandbox leak, not mine.

  It helps that most of my projects are open source so I don't need to worry about prompt injection code stealing vulnerabilities. That way the worst that can happen would be an attack adding a vulnerability to my code that I don't spot when I review the PR.

  And turning off outbound networking should protect against code stealing too... but I allow access to everything because I don't need to worry about code stealing and that way Claude can install things and run benchmarks and generally do all sorts of other useful bits and pieces.

  • binsquare

    today at 10:11 PM

    hey fren, try this: https://github.com/smol-machines/smolvm

    I already have a couple folks using it for claude: https://github.com/smol-machines/smolvm/discussions/3

• today at 9:23 PM

I appreciate the details in this, but I also notice it is very machine-focused. When a user wants to sandbox an AI agent, they don’t just want their local .ssh keys protected. They also want to be able to control access to a lot of off-machine resources - e.g. allowing the agent to read github issues and sometimes also make some kinds of changes.

QubesOS was built to give sandboxes kernel isolation via a hypervisor.

It’s not surprising that most people don’t know about it, because QubesOS as a daily driver can be painful. But with some improvements, I think it’s the right way to do it.

• diacritical

  today at 9:15 PM

  Just posted about Qubes a minute after you did, but I don't find it painful or even time consuming. Initially there was a learning curve, but even if the security of Qubes became the same as the security of a baremetal OS, I would still use it.

  When I'm trying to get some software up and running, I've had issues with Debian many times, as well as with Fedora. Rarely with both. With Qubes after a few minutes of trying on Debian and running into some obscure errors, I can just say "fuck it" and try with Fedora, or vice versa. Over the years it has saved me more time than the time I've invested it learning how Qubes works or dealing with Qubes-specific issues.

  I also don't have to care about polluting my OS with various software and running into a dependency hell.

  If a VM crashes or hangs, it's usually OK, as it's just a VM.

  It's much easier to run Whonix or VPNs without worrying for IP leaks.

Sandbox isolation is only slightly important, you don't need to make it fancy, just a plain old VM. The really important thing is how you control capabilities you give for the agent to act on your behalf.

• yoyohello13

  today at 9:36 PM

  But managing granular permissions is hard. The common denominator with all these discussions is people want to apply the minimal amount of thinking possible.

  • jbverschoor

    today at 9:41 PM

    1) can access/write local files?

    2) can access/write a specific folder?

    3) can access network?

    4) can access gateway/internet?

    5) can access local network? (vlans would help here)

    6) give access to USB devices

    7) needs access to the screen? -> giveframebuffer access / drawing primitive

    8) Need to write? Use an overlay FS that can be checked by the host and approved

    9) sub processes can never escalate permissions

    By default: nothing. But unfortunately, it’s always by default allow.

    Also, make it simple to remove the permissions again.

Its worth pointing out another boundary: speculative execution. If sensitive data is in process memory with a WASM VM it can be read even if the VM doesn't expose it. This is also true of multiple WASM VMs running for different parties. For WASM isolation to work the VM needs to be in a seperate process

> compute isolation means nothing if the sandbox can freely phone home.

Here's a project I've been working on to address the network risk. Uses nftables firewall allowing outbound traffic only to an explicit pinned domain allowlist (continuously refreshes DNS resolutions in the background).

https://github.com/noperator/cagent

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