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This file contains tips to help you take (and understand) your first steps in the world of Theia development. Are you in a hurry? See the Quick Start.

How to build Theia and the example applications

Theia is a framework to build IDEs, so you can't really "run" Theia itself. However, you can run the example applications included in its repository. One is a browser-based IDE and the other is the Electron-based equivalent.

The following instructions are for Linux and macOS.

For Windows instructions click here.


  • Node.js >= 14.
    • We recommend using Node's LTS: currently 16.x
    • If you are interested in Theia's VS Code Extension support then you should use a Node version at least compatible with the one included in the version of Electron used by VS Code.
  • Yarn package manager >= 1.7.0 AND < 2.x.x.
  • git (If you would like to use the Git-extension too, you will need to have git version 2.11.0 or higher.)
  • Python3 is required for the build due to node-gyp@8.4.1

Some additional tools and libraries are needed depending on your platform:

  • Linux

    • make
    • gcc (or another compiling toolchain)
    • pkg-config
    • build-essential: sudo apt-get install build-essential
    • native-keymap native node module dependencies:
      • Debian-based: sudo apt-get install libx11-dev libxkbfile-dev
      • Red Hat-based: sudo yum install libX11-devel.x86_64 libxkbfile-devel.x86_64 # or .i686
      • FreeBSD: sudo pkg install libX11
    • keytar native node module dependencies (reference):
      • Debian/Ubuntu: sudo apt-get install libsecret-1-dev
      • Red Hat-based: sudo yum install libsecret-devel
      • Arch Linux: sudo pacman -S libsecret
      • Alpine: apk add libsecret-dev
  • Linux/MacOS

    • nvm is recommended to easily switch between Node.js versions.
  • Windows

    • We recommend using scoop. The detailed steps are here.

Quick Start

To build and run the browser example:

git clone \
    && cd theia \
    && yarn \
    && yarn download:plugins \
    && yarn browser build \
    && yarn browser start

Start your browser on http://localhost:3000.

To build and run the Electron example:

git clone \
    && cd theia \
    && yarn \
    && yarn download:plugins \
    && yarn electron build \
    && yarn electron start

Download plugins

You can download plugins to use with the examples applications by running:

yarn download:plugins

Run the browser example with SSL

To run the browser example using SSL use:

git clone \
    && cd theia \
    && yarn \
    && yarn browser build \
    && yarn download:plugins \
    && yarn browser start --ssl --cert /path/to/cert.crt --certkey /path/to/certkey.key

Start your browser on https://localhost:3000.

Run the browser example with Gitpod

Gitpod is a Theia-based IDE for GitHub. You can start by prefixing any GitHub URL in the Theia repository with

yarn browser start ../.. --hostname

Clone the repository

git clone

The directory containing the Theia repository will now be referred to as $THEIA, so if you want to copy-paste the examples, you can set the THEIA variable in your shell:


The repository structure

Theia repository has multiple folders:

  • packages folder contains runtime packages, as the core package and extensions to it
  • dev-packages folder contains devtime packages
    • @theia/cli is a command line tool to manage Theia applications
    • @theia/ext-scripts is a command line tool to share scripts between Theia runtime packages
  • examples folder contains example applications, both Electron-based and browser-based
  • doc folder provides documentation about how Theia works
  • scripts folder contains JavaScript scripts used by npm scripts when installing
  • the root folder lists dev dependencies and wires everything together with Lerna

Build core, extensions and examples packages

You can download dependencies and build TypeScript packages using:


This command downloads dev dependencies, links and builds all TypeScript packages.

To build the example applications:

yarn browser build
yarn electron build

# build both example applications at once:
yarn build:examples

To learn more and understand precisely what's going on, please look at scripts in package.json.

Build Everything

yarn all

This will install dependencies, link and build TypeScript packages, lint, and build the example applications.

Build TypeScript sources

Dependencies must be installed before running this command.

yarn compile


Linting takes a lot of time, this is a limitation from ESLint. We always lint in the GitHub Workflows, but if you want to lint locally you have to do it manually:

yarn # build TypeScript
yarn lint # lint TypeScript sources

Note that yarn all does linting.

Build extension packages individually

From the root:

npx run compile @theia/package-name

From the package:

yarn compile

Run the browser-based example application

We can start the application from the examples/browser directory with:

yarn start

This command starts the backend application listening on port 3000. The frontend application should be available on http://localhost:3000.

If you rebuild native Node.js packages for Electron then rollback these changes before starting the browser example by running from the root directory:

yarn browser rebuild

Run the Electron-based example application

yarn electron start


Rebuilds everything: TypeScript and example applications.

yarn build


Watch the TypeScript packages

To run TypeScript in watch-mode so that TypeScript files are compiled as you modify them:

yarn watch:compile

Watch the core and extension packages

To rebuild everything each time a change is detected run:

yarn watch:all

Watch the examples

To rebuild each time a change is detected in frontend or backend you can run:

# either
yarn browser watch

# or
yarn electron watch

Watch a specific package

You can use npx to watch a single package:

npx run watch @theia/the-package-name

Watch a specific package and its local upstream dependencies

Using TypeScript build mode

Once you have built all TypeScript packages once, making a single change and recompiling should be rather quick.

Given this, you can efficiently watch the whole monorepo using TypeScript build mode and have it quickly compiled.

See Watch the TypeScript packages.

In this mode, TypeScript only compiles what changed along with its dependents.

Using Theia's run utility

Let assume you have to work for instance in the @theia/navigator extension. But you might have to apply changes in any of its upstream dependencies such as @theia/filesystem or @theia/core, you can either do yarn watch which could be super expensive, as it watches all the packages. Or you can do npx run watch @theia/navigator and npx run watch @theia/filesystem and npx run watch @theia/core in three individual shells. Or you can do the following single-liner:

npx run watch @theia/navigator --include-filtered-dependencies --parallel


Debug the browser example's backend

  • Open the debug view and run the Launch Browser Backend configuration.

Debug the browser example's frontend

  • Start the backend by using yarn run start.
  • In a browser: Open http://localhost:3000/ and use the dev tools for debugging.
  • Open the debug view and run the Launch Browser Frontend configuration.

Debug the browser example's frontend and backend at the same time

  • Open the debug view and run the Launch Browser Backend configuration.
  • Then run the Launch Browser Frontend configuration.

Debug the Electron example's backend

  • Open the debug view and run the Launch Electron Backend configuration.

Debug the Electron example's frontend

  • Start the Electron backend
    • Either open the debug view and run the Launch Electron Backend configuration
    • Or use yarn run start.
  • Attach to the Electron Frontend
    • Either open the debug view and run the Attach to Electron Frontend configuration
    • Or in Electron: Help -> Toggle Electron Developer Tools.

Debug the Electron example's frontend and backend at the same time

  • Open the debug view and run the Launch Electron Backend & Frontend configuration.

Debug IPC servers

  • Pass --${server-name}-inspect arg to the backend server.
  • Attach the debugger to the logged port.

In order to look up server-name run the backend server with --log-level=debug flag to enable logging of IPC servers instantiation. You should be able to see message of [${server-name}: ${server-PID}]: IPC started format, like [nsfw-watcher: 37557] IPC started.

Debug the plugin host

  • Pass --hosted-plugin-inspect=9339 arg to the backend server from the command line.
    • Instead you can run Launch Browser Backend launch configuration which is already pre-configured.
  • Open the debug view and run the Attach to Plugin Host launch configuration.
    • It connects to the plugin host if at least one extension is detected, otherwise it timeouts after 60s.
    • If you want to debug the activation then enable stopOnEntry flag.
  • Open the browser page.

Debugging Plugin Sources

click for base article

The following launch configuration is meant to be used when the Theia project is opened as the main project in vscode, the following launch configuration is added inside .vscode/launch.json.

  • The source repository of your plugin is expected under your ${workspaceFolder}/plugins folder
  • You can start the frontend from URL: http://localhost:3030
  • It's suggested to update your frontend launch configuration URL to open your favorite target project in a second launch

Launch configuration template that will start the backend process, and then attempt to connect on port 9339 to debug the plugin-host sub-process:

    "name": "Launch VS Code extension as Theia plugin",
    "type": "node",
    "request": "launch",
    "port": 9339,
    "timeout": 100000,
    "args": [
        "--hosted-plugin-inspect=9339", // spawn the plugin-host in debug mode
    "stopOnEntry": false,
    "sourceMaps": true,
    "outFiles": [
    "internalConsoleOptions": "openOnSessionStart",
    "outputCapture": "std"

Producing typescript maps for your plugin

Enable source maps in the plugin's tsconfig.json

    "compilerOptions": {
        "sourceMap": true

If Webpack is used you should bundle in development mode in the package.json scripts to avoid minification:

webpack --mode development

As well as enabling source map output in the webpack.config.js

module.exports = {
    devtool: 'source-map'

Compiling and blocking typescript from walking up parent directories (see discussion)

If you get errors while building like:

(parent folders)/index.d.ts: error TS2300: Duplicate identifier

You can fix it by modifying your tsconfig.json:

    "compilerOptions": {
       "typeRoots": ["./node_modules/@types"]


  • Use Chrome devtools to profile both the frontend and backend (Node.js).
    • For Node.js: open chrome://inspect, click the configure button and ensure target host and port are listed.
  • Learn how to get and understand CPU measurements:
  • Learn how to get and understand Memory measurements:
  • Before taking the memory snapshot always collect garbage.
  • Make sure that Chrome extensions don't distort measurements by disabling them.
    • For frontend: React extension is leaking components.
  • Make measurements before and after improvements to provide them as evidence on a pull request.
    • Also document how to reproduce improved measurements in How to test section of a pull request description.
  • If objects don't have a proper class, i.e. plain JSON, then find one of them in the first snapshot and check that it is garbage collected in the diff between snapshots.

Profile the frontend process

  • In Browser: open the devtools.
  • In Electron: Help -> Toggle Electron Developer Tools.

Profile the backend process

Profile IPC servers

Profile the plugin host


Code coverage

yarn run test

By default, this will generate the code coverage for the tests in an HTML format, which can be easily viewed with your browser (Chrome/Firefox/Edge/Safari etc.) by opening packages/<package name>/coverage/index.html.

Building on Windows

  • Install scoop.
  • Install nvm with scoop: scoop install nvm.
  • Install Node.js with nvm: nvm install 12.14.1, then use it: nvm use 12.14.1. You can list all available Node.js versions with nvm list available if you want to pick another version.
  • Install yarn: scoop install yarn.
  • If you need to install windows-build-tools, see Installing Windows Build Tools.
  • If you run into problems with installing the required build tools, the node-gyp documentation offers a useful guide how to install the dependencies manually. The versions required for building Theia are:
  • If you have multiple versions of either python or Visual Studio installed or if the tool is not found, you may adjust the used version via the npm config:
    • npm config set python /path/to/executable/python --global
    • npm config set msvs_version 2017 --global

Clone, build and run Theia. Using Git Bash as administrator:

git clone \
    && cd theia \
    && yarn \
    && yarn browser build \
    && yarn browser start

If you do not have Git Bash installed on your system, get one, or use scoop: scoop install git.

Installing Windows Build Tools

  • Previously, windows-build-tools is required to build Native Nodes modules on Windows. The npm package is now deprecated because NodeJS installer can now install all the required tools that it needs, including Windows Build Tools.
  • In case you need to install the tool manually, after installing yarn, run PowerShell as Administrator and copy paste the following: npm --add-python-to-path install --global --production windows-build-tools.


First make sure that you follow the steps given in the docs correctly.


The start command will start a watcher on many files in the theia directory. To avoid ENOSPC errors, increase your default inotify watches.

It can be done like so:

echo fs.inotify.max_user_watches=524288 | sudo tee -a /etc/sysctl.conf && sudo sysctl -p


If you see LINK : fatal error LNK1104: cannot open file 'C:\\Users\\path\\to\\node.lib' [C:\path\to\theia\node_modules\drivelist\build\drivelist.vcxproj], then set the Visual Studio version manually with npm config set msvs_version 2017 --global.

If you are facing with EPERM: operation not permitted or permission denied errors while building, testing or running the application then;

  • You don't have write access to the installation directory.
  • Try to run your command line (PowerShell, GitBash, Cygwin or whatever you are using) as an administrator.
  • The permissions in the NPM cache might get corrupted. Please try to run npm cache clean to fix them.
  • If you experience issues such as Error: EBUSY: resource busy or locked, rename, try to disable (or uninstall) your anti-malware software. See here.
  • Still having issues on Windows? File a [bug]. We are working on Linux or OS X operating systems. Hence we are more than happy to receive any Windows-related feedbacks, bug reports.

If you're still struggling with the build but you use Windows 10, the you can enable the Windows Subsystem for Linux and you can get a Linux distro for free.


You need to have the Xcode command line tools installed in order to build and run Theia. You can install the tools by running

xcode-select --install

If you already have Xcode installed, but you see the xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance error, you need to run the following command to fix it: sudo xcode-select --switch /Library/Developer/CommandLineTools.

The solution is the same if you have updated to 10.14 (Mojave) and you can see the gyp: No Xcode or CLT version detected! error. More details here.

Root privileges errors

When trying to install with root privileges, you might encounter errors such as cannot run in wd.

Several options are available to you:

  • Install without root privileges
  • Use the --unsafe-perm flag: yarn --unsafe-perm