Announcing the Haskell Error Index

The Haskell Error Index is a community-driven web site for improving the documentation of Haskell tooling. In the upcoming release of GHC, each error message or warning includes a unique code. This code can be looked up on the index to find user-contributed explanations and examples. As the specific phrasing of messages in GHC is improved over time, the codes will remain constant, which allows the documentation on the site to retain its value and its search-engine usefulness.

The site is run off of a Git repo full of Markdown files and example programs, so you don’t need to be an expert to contribute. Contributions of documentation as well as technical improvements to the site generator, HTML, and CSS are all very welcome. Most of the current content and infrastructure was contributed by volunteers at Zurihac this year.

Right now, it only covers an unreleased version of GHC, but the system is set up to also work with other tools. If you’re an author of Haskell-related tooling and would like to have it included, please write to me at

The site is inspired by the Rust error index and by the excellent user-contributed sections in the PHP documentation. It’s part of the Haskell Foundation’s technical agenda, arising from a Haskell Foundation Technical Proposal. If you’d like to have influence on what we at the HF do, please submit a proposal!


Thank you, our leader!

Glad to see things are happening. Really liked your speech at the Haskell’22, and the vision of the Haskell decade for tooling.

I must admit that when you first took the chair, I thought we would be going to the alley of more dependently-typed features. But it seems we are actually going on a more industry friendly vision. Hooray!


Don’t get me wrong - I love dependent types! But I don’t think that working on dependently-typed programming is anything close to being where the HF and I can bring the most value to the Haskell community. There’s plenty of people doing dependent types well, and I’m not here to push my own interests and loves.

I’m glad you liked the talk, and I hope that the errors site is useful for you.


This is a fantastic project. I have high hopes for it.