Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.
Latest commit message
Commit time

Run the Coq Proof Assistant in your browser!

Build Status

jsCoq is an Online Integrated Development Environment for the Coq proof assistant and runs in your browser! We aim to enable new UI/interaction possibilities and to improve the accessibility of the Coq platform itself. Current stable version is jsCoq 0.16.0 supporting Coq 8.16.0, try it:

jsCoq is written to conform to ES2017; any recent standard-compliant browser should be able to run it. No servers or external programs are needed. See the Troubleshooting section if you have problems.

jsCoq is community-developed by a team of contributors.

Are you a jsCoq user?

Have you developed or taught a course using jsCoq? Do you have some feedback for us?

If so, please submit a pull request or an issue so we can add your lectures to the list of jsCoq users. This is essential to guarantee future funding of the project.

Basic Usage

The main page showcases jsCoq by walking through a proof for the infinitude of primes using math-comp, due to Georges Gonthier.

Once jsCoq finishes loading, you can step through the proof using the arrow buttons on the toolbar (top right), or using these keyboard shortcuts:

Shortcut Action
Alt-N or Alt-↓ Go to next
Alt-P or Alt-↑ Go to previous
Alt-Enter or Alt-→ Go to cursor

You can open a blank editor and experiment with your own Coq developments using the scratchpad. The same keyboard shortcuts apply here.

The scratchpad's contents are saved in your browser's local storage (IndexedDB, specifically), so they are not lost if you close the browser window or refresh the page. You can, in fact, store more than one document using the local open/save file dialogs:

Shortcut Action
Ctrl-S Save file (with the last name provided, or untitled.v)
Ctrl-Shift-S Save file as (prompts for file name; also has options to download or share the content)
Ctrl-Alt-S Save file to disk (using the browser's Save dialog, or preset destination)
Ctrl-O Open file (prompts for file name, supports tab completion)
Ctrl-Alt-O Open file from disk (using the browser's Open dialog)

On Mac, replace Ctrl with ⌘ (command) and Alt with ⌥ (option), as is traditional.

Drag .v files from your local drive onto the scratchpad to open them. You can also drag multiple files, which will open up a project pane to the left of the editor, allowing you to switch between them; this functionality is still experimental.

Sharing your development

A small pastebin-like server based on Hastebin is available for sharing .v files between users. Open the save dialog (Ctrl-Shift-S) and click "Share"; then share the URL from your browser's location bar with anyone you like. The URL represents the state of the document at the moment it was shared, and this state is read-only. Every time you click "Share", a fresh URL is generated. Shared content is not saved forever, though; documents are typically available for a period of ~30 days.

How to build your own jsCoq documents

See the dedicated page for information on advanced options and jsCoq HTML embedding API. A quick setup can be done with:

$ npm install jscoq

then copy and adapt the template page page to your needs.

For a more detailed tutorial and information, refer to docs/

Contributing and Developer Information

See the dedicated page for developer information as well as links to past versions and tools.

This is a beta-status project, but any contribution or comment is really welcome! See the contributing guide for more information.


See the dedicated file


The main page includes a proof of the infinitude of primes by G. Gonthier. We provide some more examples as a showcase of the tool:

Outdated examples [but still working]

jsCoq Users:

Incomplete list of places where jsCoq has been used:

jsCoq in the press

Addon Packages

One of jsCoq's strengths is its support for bundling addon packages. In order to add your Coq package to jsCoq, you need to compile it with jsCoq's version of Coq. Head over to jscoq/addons for pointers to some well-known packages that have been compiled for jsCoq and are bundled with every version of jsCoq. You can use these as examples for bundling your own libraries.


Are you getting a StackOverflow exception? Unfortunately these are hard to fix; you may be stuck with them for a while.

  • Clearing the browser cache usually solves lots of issues.
  • Change browser, if using Firefox try Chrome, if using Chrome try Firefox.

Reporting Bugs

Feel free to use the issue tracker. Please include your browser/OS/user-agent and any command-line options.

Contact and on-line help

What is broken

  • Loading ML modules is slow.
  • Loading .vo files is slow.
  • There surely are threading and performance problems.
  • vm_compute and native_compute fall back to regular compute.


See the etc/notes/ directory for some random notes about the project.


Core developer team

Past Contributors



jsCoq was made possible thanks to funding by the FEEVER project and support from MINES ParisTech

We want to strongly thank the js_of_ocaml developers. Without their great and quick support jsCoq wouldn't have been possible.

CodeMirror has played a crucial role in the project, we are very happy with it, thanks a lot!

Please consider supporting the development of CodeMirror with a donation.