June 18, 2026
Proof or it didn’t happen
Show HN: Talos – Open-source WASM interpreter for Lean
This new coding tool wowed proof nerds, confused everyone else, and sparked a name mix-up frenzy
TLDR: Talos is a new open-source tool that can both run WebAssembly programs and mathematically check what they’re supposed to do, which could make software more trustworthy. Commenters were intrigued but immediately split between excitement over the idea, concern about how usable it is, and jokes about confusing it with another Talos project.
A new open-source project called Talos just landed on Hacker News, and while the official pitch is very serious—basically, a way to both run WebAssembly programs and prove what they do in the same place—the real action was in the comments. The vibe was equal parts impressed, curious, and gloriously confused. One commenter from the Cajal team jumped in fast to say, yes, this is a big bet: the idea is that WebAssembly, the portable format many languages compile to, could become a prime place to check whether software behaves correctly. Translation for normal humans: build once, test deeply, and maybe trust it more.
But the hottest reaction wasn’t pure praise—it was "okay, but how painful is this for actual developers?" One of the first questions cut right to the heart of it: do people have to write all their checks in Lean, the theorem-proving language behind the project, or can they work directly from Rust? That’s the community’s biggest pressure point so far: everyone loves the dream of ultra-trustworthy software, but they also want to know whether this is practical or just catnip for proof enthusiasts.
And then came the comedy relief. Another commenter saw the name Talos and immediately thought of the existing Talos Linux project, briefly imagining native WebAssembly pod support before realizing this was a totally different Talos. In other words: one part formal methods breakthrough, one part accidental branding cliffhanger, and 100% classic Hacker News energy.
Key Points
- •Talos is an open-source WebAssembly interpreter implemented in Lean 4 and designed to use the same codebase for execution and formal reasoning.
- •The project aims to provide feature-complete executable semantics for WebAssembly while supporting theorem proving about program correctness, equivalence, and input-wide properties.
- •Talos prioritizes clarity of reasoning over execution speed, with an initial focus on Wasm features commonly generated from non-optimized Rust and C code.
- •Its proof system is built on weakest precondition calculus to support compositional proofs for loops, branches, and function calls.
- •The repository is structured as three Lake packages—Interpreter, CodeLib, and Programs—and depends on Lean 4 and wasm-tools.