Skip to content

A JSON-like data structure (a CRDT) that can be modified concurrently by different users, and merged again automatically.


Notifications You must be signed in to change notification settings


Repository files navigation


Automerge logo

homepage main docs latest docs ci docs

Automerge is a library which provides fast implementations of several different CRDTs, a compact compression format for these CRDTs, and a sync protocol for efficiently transmitting those changes over the network. The objective of the project is to support local-first applications in the same way that relational databases support server applications - by providing mechanisms for persistence which allow application developers to avoid thinking about hard distributed computing problems. Automerge aims to be PostgreSQL for your local-first app.

If you're looking for documentation on the JavaScript implementation take a look at There are other implementations in both Rust and C, but they are earlier and don't have documentation yet. You can find them in rust/automerge and rust/automerge-c if you are comfortable reading the code and tests to figure out how to use them.

If you're familiar with CRDTs and interested in the design of Automerge in particular take a look at

Finally, if you want to talk to us about this project please join our Discord server!


This project is formed of a core Rust implementation which is exposed via FFI in javascript+WASM, C, and soon other languages. Alex (@alexjg) is working full time on maintaining automerge, other members of Ink and Switch are also contributing time and there are several other maintainers. The focus is currently on shipping the new JS package. We expect to be iterating the API and adding new features over the next six months so there will likely be several major version bumps in all packages in that time.

In general we try and respect semver.


A stable release of the javascript package is currently available as @automerge/automerge@2.0.0 where. pre-release verisions of the 2.0.1 are available as 2.0.1-alpha.n. 2.0.1* packages are also available for Deno at


The rust codebase is currently oriented around producing a performant backend for the Javascript wrapper and as such the API for Rust code is low level and not well documented. We will be returning to this over the next few months but for now you will need to be comfortable reading the tests and asking questions to figure out how to use it. If you are looking to build rust applications which use automerge you may want to look into autosurgeon

Repository Organisation

  • ./rust - the rust rust implementation and also the Rust components of platform specific wrappers (e.g. automerge-wasm for the WASM API or automerge-c for the C FFI bindings)
  • ./javascript - The javascript library which uses automerge-wasm internally but presents a more idiomatic javascript interface
  • ./scripts - scripts which are useful to maintenance of the repository. This includes the scripts which are run in CI.
  • ./img - static assets for use in .md files


To build this codebase you will need:

  • rust
  • node
  • yarn
  • cmake
  • cmocka

You will also need to install the following with cargo install

  • wasm-bindgen-cli
  • wasm-opt
  • cargo-deny

And ensure you have added the wasm32-unknown-unknown target for rust cross-compilation.

The various subprojects (the rust code, the wrapper projects) have their own build instructions, but to run the tests that will be run in CI you can run ./scripts/ci/run.

For macOS

These instructions worked to build locally on macOS 13.1 (arm64) as of Nov 29th 2022.

# clone the repo
git clone
cd automerge

# install rustup
curl --proto '=https' --tlsv1.2 -sSf | sh

# install homebrew
/bin/bash -c "$(curl -fsSL"

# install cmake, node, cmocka
brew install cmake node cmocka

# install yarn
npm install --global yarn

# install javascript dependencies
yarn --cwd ./javascript

# install rust dependencies
cargo install wasm-bindgen-cli wasm-opt cargo-deny

# get nightly rust to produce optimized automerge-c builds
rustup toolchain install nightly
rustup component add rust-src --toolchain nightly

# add wasm target in addition to current architecture
rustup target add wasm32-unknown-unknown

# Run ci script

If your build fails to find cmocka.h you may need to teach it about homebrew's installation location:

export CPATH=/opt/homebrew/include
export LIBRARY_PATH=/opt/homebrew/lib


Please try and split your changes up into relatively independent commits which change one subsystem at a time and add good commit messages which describe what the change is and why you're making it (err on the side of longer commit messages). git blame should give future maintainers a good idea of why something is the way it is.


There are four artefacts in this repository which need releasing:

  • The @automerge/automerge NPM package
  • The @automerge/automerge-wasm NPM package
  • The automerge deno crate
  • The automerge rust crate

JS Packages

The NPM and Deno packages are all released automatically by CI tooling whenever the version number in the respective package.json changes. This means that the process for releasing a new JS version is:

  1. Bump the version in the rust/automerge-wasm/package.json (skip this if there are no new changes to the WASM)
  2. Bump the version of @automerge/automerge-wasm we depend on in javascript/package.json
  3. Bump the version in @automerge/automerge also in javascript/package.json

Put all of these bumps in a PR and wait for a clean CI run. Then merge the PR. The CI tooling will pick up a push to main with a new version and publish it to NPM. This does depend on an access token available as NPM_TOKEN in the actions environment, this token is generated with a 30 day expiry date so needs (manually) refreshing every so often.

Rust Package

This is much easier, but less automatic. The steps to release are:

  1. Bump the version in automerge/Cargo.toml
  2. Push a PR and merge once clean
  3. Tag the release as rust/automerge@<version>
  4. Push the tag to the repository
  5. Publish the release with cargo publish