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Show HN: Lasm – Write formally verified webapps in Lean for Node/serverless/edge

An agentic engineer released Lasm, a tool that brings the Lean programming language to browsers, Node, serverless and edge environments so developers can write formally verified web apps from frontend to backend. The developer said Lasm was built mostly by Claude Opus 5.5 under their high-level direction, and described formal verification as "the next evolution of software engineering and programming languages," enabled by LLMs that understand formal verification languages. The project was posted to Hacker News as a Show HN with 1 point and 0 comments.

read1 min views1 publishedOct 30, 2026

Lasm has been my dream for a good part of 2026. I firmly believe that formal verification is the next evolution of software engineering and programming languages. This next wave will largely be enabled by the incredibly intelligent LLMs that understand formal verification and its programming languages.

Lean is one of the most popular languages that allow for formal verification, and to me is incredibly powerful because it is a general purpose programming language with formal verification built directly into it.

You can build general purpose software in Lean, and formally verify it in Lean. Amazing.

Lasm brings Lean to the browser, Node, serverless, and edge environments (and more). The idea is that you can now write web apps, frontend to backend, in Lean and formally verify these apps.

Imagine an Express server or Hono server, running on Cloudflare Workers, with formal verification of its specification.

I'm an agentic engineer with an emphasis in software engineering, and Lasm was built mostly by Claude Opus 5.5 with my high-level direction.

Comments URL: [https://news.ycombinator.com/item?id=50299004](https://news.ycombinator.com/item?id=50299004)

Points: 1

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