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Lasm compiles Lean 4 programs to Wasm for Node, serverless and edge
The Lasm project, posted on GitHub, says it compiles Lean 4 ahead of time to WebAssembly so one codebase can run as a Node server, serverless or edge function, or browser app, with proofs on the deployed code.
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A GitHub project named Lasm describes itself as a compiler that turns Lean 4 programs into WebAssembly so the same codebase can run as a Node server, a serverless or edge function, a WASI or Fastly module, or a browser app1.
The repository README, under the Millillion organization, says Lasm compiles ordinary Lean 4 ahead of time rather than interpreting it at run time, and that because the source is Lean, developers can prove properties of the code they deploy1. It lists current version @lasm/cli 0.3.5 on npm, Lean 4.35.0 as the pinned toolchain, and Node 24 or newer (with tested Bun and Deno builds) as the compiler host1.
Documented build targets include Node, AWS Lambda and Lambda@Edge, Vercel and Netlify functions, Azure Functions, Google Cloud Functions, Cloudflare Workers, several edge runtimes, Fastly Compute, WASI and browsers1. The README says Node builds keep Lean's full runtime, while edge, Bun/Deno, WASI and browser builds run Lean single-threaded without sockets or processes1.
The flagship example, Conduit, is described as the RealWorld Medium-clone app written in Lean, with 117 theorems checked with no sorry and only Lean's standard axioms, covering authorization, pagination and related properties1. The same README says SQL, JSON, concurrency and the toolchains themselves are trusted rather than proved, and that full RealWorld spec conformance is tested, not proved1.
Lasm's own source is listed as MIT, with copyright attributed to Jordan Last; starter templates are listed as MIT-01. Independent verification of the theorem counts, CI claims and production fitness is not in the repository page we read1.
