Marijn Haverbeke

Marijn Haverbeke is a Dutch independent programmer best known as the creator of CodeMirror, the in-browser code editor, and ProseMirror, the toolkit for building rich-text editors. He also wrote Eloquent JavaScript, one of the most widely read free programming books, and the Acorn JavaScript parser. Haverbeke lives in Berlin and funds almost all of his work through sponsorships from the companies that use his libraries.

CodeMirror began in early 2007 as the console for the Eloquent JavaScript website and was first packaged as a standalone library in May 2007. After the Ace editor showed that a JavaScript editor could handle huge documents, Haverbeke rewrote it as version 2 without relying on contentEditable. Over the following decade it became the editor inside countless developer tools, browser devtools and online playgrounds. Eloquent JavaScript followed in print in 2011 and is now in its fourth edition (2024, No Starch Press), still free to read online under a Creative Commons license.

Haverbeke has written openly about the economics of open source. In a 2015 essay he argued that maintainers of widely used libraries are badly underfunded, rejected dual licensing as too restrictive, and settled on a model of permissive MIT licensing combined with a clear social expectation that commercial users pay. He crowdfunded the code-analysis tool Tern, then ran an Indiegogo campaign in 2015 to fund the first version of ProseMirror, which reached 1.0 in October 2017. Mozilla's MOSS program supported the ground-up rewrite that became CodeMirror 6, together with the Lezer incremental parser; CodeMirror 6.0 shipped in June 2022.

Today his funding page offers companies monthly tiers from 100 to 1,000 euros, with perks like logo placement and guaranteed attention to their issues, while smaller supporters use GitHub Sponsors or Patreon. In a 2021 interview he said Acorn earns essentially nothing but that CodeMirror and ProseMirror have enough serious corporate sponsors to pay his bills.

In July 2026 he released Wordgard 0.1, a new semantic rich-text editor library built on lessons from ProseMirror, while continuing to maintain ProseMirror and CodeMirror. Haverbeke matters to the indie world as one of the clearest proofs that a single developer can sustain foundational open-source infrastructure, used by companies of every size, without venture money or a parent company.