Loogle is a search tool for Lean/Mathlib, and can be used on the web, via a zulip bot, via APIs, from VSCode or nvim extensions as a Lean command or a command line tool.

Try it at https://loogle.lean-lang.org/!

$ loogle '(List.replicate (_ + _) _ = _)'
Found 5 definitions mentioning List.replicate, HAdd.hAdd and Eq.
Of these, 3 match your patterns.


Running locally

To use loogle locally:

  1. check out this repository
  2. install elan
  3. run lake exe cache get
  4. run lake exe loogle --help (or other options)

If you use loogle on a large repository like Mathlib, the startup-time will be rather large. Run lake build LoogleMathlibCache if you want to pre-compute the index for Mathlib.

CLI Usage

  loogle [OPTIONS] [QUERY]

  --interactive, -i     read querys from stdin
  --json, -j            print result in JSON format
  --module mod          import this module (default: Mathlib)
  --path path           search for .olean files here (default: the build time path)
  --write-index file    persists the search index to a file
  --read-index file     read the search index from a file. This file is blindly trusted!

By default, it will create an internal index upon starting, which takes a bit. You can use --write-index and --read-index to cache that, but it is your responsibility to pass the right index for the given module and search path. In the nix setup, the index is built as part of the build process.

Web service

This tools is the backend of https://loogle.lean-lang.org/. This is currently running on a 4GB Hetzner virtual host with a nixos system (see ./nixos) with a ngingx reverse proxy (for SSL) in front of a small python HTTP server (see ./server.py) that uses loogle. The query processing is locked down using SECCOMP (see ./loogle_seccomp.c). It automatically tries to upgrade to the latest mathlib every 6 hours. See ./service for the NixOS configuration for the server.

You can run this server locally as well, either using ./server.py after you built loogle via lake.

At the path /json?q=… (instead of /?q=…), the result is returned in JSOON format. No stability of the format is guaranteed at this point.

Zulip bot

The leanprover Zulip chat has a bot called loogle that will respond to messages with the first two hits from loogle. Just write @**loogle** query in a public stream.

It is implemented via an outgoing webhook to the above web service.

Editor integration

These are created by their respective maintainers; reach out to them if you have questions


This tool was created by Joachim Breitner <mail@joachim-breitner.de>. Feel free to use this repository to report issues or (even better) submit PRs that resolves such issues.