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Tags: programming Google editor xi
Clipped on: 2016-10-12

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Xi Editor

A modern editor with a backend written in Rust.

The xi editor project is an attempt to build a high quality text editor, using modern software engineering techniques. It is initially built for Mac OS X, using Cocoa for the user interface, but other targets are planned.

Goals include:

  • Insanely high performance. All editing operations should commit and paint in under 16ms. The editor should never make you wait for anything.

  • Beauty. The editor should fit well on a modern desktop, and not look like a throwback from the ’80s or ’90s. Text drawing should be done with the best technology available (Core Text on Mac, DirectWrite on Windows, etc.), and support Unicode fully.

  • Reliability. Crashing, hanging, or losing work should never happen.

  • Developer friendliness. It should be easy to customize xi editor, whether by adding plug-ins or hacking on the core.

Screenshot (will need to be updated as syntax coloring and UI polish is added):

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Getting started

You need Xcode 7.3 (only on Mac) and Rust (version 1.10+ is recommended and supported). You should have  cargo  in your path.

normal> git clone
> cd xi-editor
> xcodebuild
> open build/Release/

Or  open XiEditor.xcodeproj  and hit the Run button.

It will look better if you have InconsolataGo installed, a customized version of Inconsolata tuned for code editing. You can change fonts per window in the Font menu or with  Cmd-T . To choose another default font, edit the  CTFontCreateWithName()  call in EditView.swift.

Building the core

If you’re not on a Mac, you can build just the core like so:

normal> cd rust
> cargo build

See the xi_glium project for an experimental front-end in Rust. There are notes (I wouldn’t call it documentation at this point) on the protocol at

Design decisions

Here are some of the design decisions, and motivation why they should contribute to the above goals:

  • Separation into front-end and back-end modules. The front-end is responsible for presenting the user interface and drawing a screen full of text. The back-end (also known as “core”) holds the file buffers and is responsible for all potentially expensive editing operations.

  • Native UI. Cross-platform UI toolkits never look and feel quite right. The best technology for building a UI is the native framework of the platform. On Mac, that’s Cocoa.

  • Rust. The back-end needs to be extremely performant. In particular, it should use little more memory than the buffers being edited. That level of performance is possible in C++, but Rust offers a much more reliable, and in many ways, higher level programming platform.

  • A persistent rope data structure. Persistent ropes are efficient even for very large files. In addition, they present a simple interface to their clients - conceptually, they're a sequence of characters just like a string, and the client need not be aware of any internal structure.

  • Asynchronous operations. The editor should never, ever block and prevent the user from getting their work done. For example, autosave will spawn a thread with a snapshot of the current editor buffer (the persistent rope data structure is copy-on-write so this operation is nearly free), which can then proceed to write out to disk at its leisure, while the buffer is still fully editable.

  • Plug-ins over scripting. Most text editors have an associated scripting language for extending functionality. However, these languages are usually both more arcane and less powerful than “real” languages. The xi editor will communicate with plugins through pipes, letting them be written in any language, and making it easier to integrate with other systems such as version control, deeper static analyzers of code, etc.

  • JSON. The protocol for front-end / back-end communication, as well as between the back-end and plug-ins, is based on simple JSON messages. I considered binary formats, but the actual improvement in performance would be completely in the noise. Using JSON considerably lowers friction for developing plug-ins, as it’s available out of the box for most modern languages, and there are plenty of the libraries available for the other ones.

Current status

This is still a project in its early stages. The Mac build has basic editing functionality (it was used to write this README), but looks very spare and is still missing essentials such as syntax highlighting and auto-indent. At the moment, it’s expected that its main community will be developers interested in hacking on a text editor.


The main author is Raph Levien.


We gladly accept contributions via GitHub pull requests, as long as the author has signed the Google Contributor License. Please see for more details.


This is not an official Google product (experimental or otherwise), it is just code that happens to be owned by Google.