Monty: A minimal, secure Python interpreter written in Rust for use by AI
1–10 of 179 posts
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#2> Instead, it let's you run safely run Python code written by an LLM embedded in your agent, with startup times measured in single digit microseconds not hundreds of milliseconds.
Perhaps if the interpreter is in turn embedded in the executable and runs in-process, but even a do-nothing `uv` invocation takes ~10ms on my system.
I like the idea of a minimal implementation like this, though. I hadn't even considered it from an AI sandboxing perspective; I just liked the idea of a stdlib-less alternative upon which better-thought-out "core" libraries could be stacked, with less disk footprint.
Have to say I didn't expect it to come out of Pydantic.
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#3I'm of the mind that it will be better to construct more strict/structured languages for AI use than to reuse existing ones.
My reasoning is 1) AIs can comprehend specs easily, especially if simple, 2) it is only valuable to "meet developers where they are" if really needing the developers' history/experience which I'd argue LLMs don't need as much (or only need because lang is so flexible/loose), and 3) human languages were developed to provide extreme human subjectivity which is way too much wiggle-room/flexibility (and is why people have to keep writing projects like these to reduce it).
We should be writing languages that are super-strict by default (e.g. down to the literal ordering/alphabetizing of constructs, exact spacing expectations) and only having opt-in loose modes for humans and tooling to format. I admit I am toying w/ such a lang myself, but in general we can ask more of AI code generations than we can of ourselves.
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#4I like the idea a lot but it's still unclear from the docs what the hard security boundary is once you start calling LLMs - can it avoid "breaking out" into the host env in practice?
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#5I got a WebAssembly build of this working and fired up a web playground for trying it out: https://simonw.github.io/research/monty-wasm-pyodide/demo.ht...
It doesn't have class support yet!
But it doesn't matter, because LLMs that try to use a class will get an error message and rewrite their code to not use classes instead.
Notes on how I got the WASM build working here: https://simonwillison.net/2026/Feb/6/pydantic-monty/
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#6Well I love the name, so definitely trying this out later, but first...
And now for something, completely different.
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#7> Instead, it let's you run safely run Python code written by an LLM embedded in your agent, with startup times measured in single digit microseconds not hundreds of milliseconds. Perhaps if the interpreter is in turn embedded in the executable and runs in-process, but even a do-nothing `uv` invocation takes ~10ms on my system. I like the idea of a minimal implementation like this, though. I hadn't even considered it…
Pydantic + FastAPI are my two favorite python shops right now, they’re always dropping fun new projcts
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#8This feels like the time I was a Mercurial user before I moved to Git.
Everyone was using git for reasons to me that seemed bandwagon-y, when Mercurial just had such a better UX and mental model to me.
Now, everyone is writing agent `exec`s in Python, when I think TypeScript/JS is far better suited for the job (it was always fast + secure, not to mention more reliable and information dense b/c of typing).
But I think I'm gonna lose this one too.
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#9If we’re going to have LLMs write the code, why not something more performant? Like pages and pages of Java maybe?
Re: Monty: A minimal, secure Python interpreter written in Rust for use by AI
#10It is absurd for any user to use a half baked Python interpreter, also one that will always majorly lag behind CPython in its support. I advise sandboxing CPython instead using OS features.