LeanHTTP: A HTTP Client for Lean 4

By Harsh Gupta · September 21, 2026

Introducing leanhttp, a HTTP client for Lean 4.

GitHub: https://github.com/theoriclabs/leanhttp

This is part of a larger toolset I've been building around writing general purpose software in Lean:

• LeanReact for UIs
• LeanDB for database interactions
• Lean’s existing HTTP server support
• now, leanhttp for outbound HTTP/HTTPS requests

Writing an application in Lean does not automatically make the application correct or formally verified. The hard part is preserving the semantics across boundaries.

In the next few posts, I’ll show how to do that.