diff --git a/packages/xo-common/.editorconfig b/packages/xo-common/.editorconfig
new file mode 100644
index 000000000..b6db0112a
--- /dev/null
+++ b/packages/xo-common/.editorconfig
@@ -0,0 +1,65 @@
+# http://EditorConfig.org
+#
+# Julien Fontanet's configuration
+# https://gist.github.com/julien-f/8096213
+
+# Top-most EditorConfig file.
+root = true
+
+# Common config.
+[*]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespaces = true
+
+# CoffeeScript
+#
+# https://github.com/polarmobile/coffeescript-style-guide/blob/master/README.md
+[*.{,lit}coffee]
+indent_size = 2
+indent_style = space
+
+# Markdown
+[*.{md,mdwn,mdown,markdown}]
+indent_size = 4
+indent_style = space
+
+# Package.json
+#
+# This indentation style is the one used by npm.
+[/package.json]
+indent_size = 2
+indent_style = space
+
+# Jade
+[*.jade]
+indent_size = 2
+indent_style = space
+
+# JavaScript
+#
+# Two spaces seems to be the standard most common style, at least in
+# Node.js (http://nodeguide.com/style.html#tabs-vs-spaces).
+[*.{js,jsx,ts,tsx}]
+indent_size = 2
+indent_style = space
+
+# Less
+[*.less]
+indent_size = 2
+indent_style = space
+
+# Sass
+#
+# Style used for http://libsass.com
+[*.s[ac]ss]
+indent_size = 2
+indent_style = space
+
+# YAML
+#
+# Only spaces are allowed.
+[*.yaml]
+indent_size = 2
+indent_style = space
diff --git a/packages/xo-common/.gitignore b/packages/xo-common/.gitignore
new file mode 100644
index 000000000..827e4e420
--- /dev/null
+++ b/packages/xo-common/.gitignore
@@ -0,0 +1,7 @@
+/dist/
+/node_modules/
+
+npm-debug.log
+npm-debug.log.*
+pnpm-debug.log
+pnpm-debug.log.*
diff --git a/packages/xo-common/.npmignore b/packages/xo-common/.npmignore
new file mode 100644
index 000000000..c31ee82cb
--- /dev/null
+++ b/packages/xo-common/.npmignore
@@ -0,0 +1,10 @@
+/examples/
+example.js
+example.js.map
+*.example.js
+*.example.js.map
+
+/test/
+/tests/
+*.spec.js
+*.spec.js.map
diff --git a/packages/xo-common/.travis.yml b/packages/xo-common/.travis.yml
new file mode 100644
index 000000000..1a582c426
--- /dev/null
+++ b/packages/xo-common/.travis.yml
@@ -0,0 +1,9 @@
+language: node_js
+node_js:
+  - stable
+  - 6
+  - 4
+
+# Use containers.
+# http://docs.travis-ci.com/user/workers/container-based-infrastructure/
+sudo: false
diff --git a/packages/xo-common/README.md b/packages/xo-common/README.md
new file mode 100644
index 000000000..987ed83fd
--- /dev/null
+++ b/packages/xo-common/README.md
@@ -0,0 +1,49 @@
+# xo-common [![Build Status](https://travis-ci.org/vatesfr/xo-common.png?branch=master)](https://travis-ci.org/vatesfr/xo-common)
+
+> Code shared between [XO](https://xen-orchestra.com) server and clients
+
+## Install
+
+Installation of the [npm package](https://npmjs.org/package/xo-common):
+
+```
+> npm install --save xo-common
+```
+
+## Usage
+
+**TODO**
+
+## Development
+
+```
+# Install dependencies
+> npm install
+
+# Run the tests
+> npm test
+
+# Continuously compile
+> npm run dev
+
+# Continuously run the tests
+> npm run dev-test
+
+# Build for production (automatically called by npm install)
+> npm run build
+```
+
+## Contributions
+
+Contributions are *very* welcomed, either on the documentation or on
+the code.
+
+You may:
+
+- report any [issue](https://github.com/vatesfr/xo-common/issues)
+  you've encountered;
+- fork and create a pull request.
+
+## License
+
+AGPL3 © [Vates SAS](https://vates.fr)
diff --git a/packages/xo-common/api-errors.js b/packages/xo-common/api-errors.js
new file mode 100644
index 000000000..3b3e7974b
--- /dev/null
+++ b/packages/xo-common/api-errors.js
@@ -0,0 +1 @@
+module.exports = require('./dist/api-errors')
diff --git a/packages/xo-common/package.json b/packages/xo-common/package.json
new file mode 100644
index 000000000..4baedd801
--- /dev/null
+++ b/packages/xo-common/package.json
@@ -0,0 +1,83 @@
+{
+  "name": "xo-common",
+  "version": "0.1.0",
+  "license": "AGPL-3.0",
+  "description": "Code shared between [XO](https://xen-orchestra.com) server and clients",
+  "keywords": [],
+  "homepage": "https://github.com/vatesfr/xo-common",
+  "bugs": "https://github.com/vatesfr/xo-common/issues",
+  "repository": {
+    "type": "git",
+    "url": "https://github.com/vatesfr/xo-common.git"
+  },
+  "author": {
+    "name": "Julien Fontanet",
+    "email": "julien.fontanet@isonoe.net"
+  },
+  "preferGlobal": false,
+  "bin": {},
+  "files": [
+    "dist/",
+    "*.js"
+  ],
+  "engines": {
+    "node": ">=4"
+  },
+  "dependencies": {
+    "babel-runtime": "^6.18.0",
+    "lodash": "^4.16.6",
+    "make-error": "^1.2.1"
+  },
+  "devDependencies": {
+    "babel-cli": "^6.18.0",
+    "babel-eslint": "^7.1.0",
+    "babel-plugin-lodash": "^3.2.9",
+    "babel-plugin-transform-runtime": "^6.15.0",
+    "babel-preset-env": "^1.0.0",
+    "babel-preset-stage-0": "^6.16.0",
+    "cross-env": "^3.1.3",
+    "dependency-check": "^2.6.0",
+    "ghooks": "^1.3.2",
+    "rimraf": "^2.5.4",
+    "standard": "^8.5.0"
+  },
+  "scripts": {
+    "build": "cross-env NODE_ENV=production babel --source-maps --out-dir=dist/ src/",
+    "clean": "rimraf dist/",
+    "depcheck": "dependency-check ./package.json --entry api-errors.js",
+    "dev": "cross-env NODE_ENV=development babel --watch --source-maps --out-dir=dist/ src/",
+    "lint": "standard",
+    "posttest": "npm run lint && npm run depcheck",
+    "prebuild": "npm run clean",
+    "predev": "npm run clean",
+    "prepublish": "npm run build"
+  },
+  "babel": {
+    "plugins": [
+      "lodash"
+    ],
+    "presets": [
+      [
+        "env",
+        {
+          "targets": {
+            "browsers": "> 1%",
+            "node": 4
+          }
+        }
+      ],
+      "stage-0"
+    ]
+  },
+  "standard": {
+    "ignore": [
+      "dist"
+    ],
+    "parser": "babel-eslint"
+  },
+  "config": {
+    "ghooks": {
+      "commit-msg": "npm test"
+    }
+  }
+}
diff --git a/packages/xo-common/src/api-errors.js b/packages/xo-common/src/api-errors.js
new file mode 100644
index 000000000..abd57e3d7
--- /dev/null
+++ b/packages/xo-common/src/api-errors.js
@@ -0,0 +1,166 @@
+import { BaseError } from 'make-error'
+import { isArray, iteratee } from 'lodash'
+
+class XoError extends BaseError {
+  constructor ({ code, message, data }) {
+    super(message)
+    this.code = code
+    this.data = data
+  }
+
+  toJsonRpcError () {
+    return {
+      message: this.message,
+      code: this.code,
+      data: this.data
+    }
+  }
+}
+
+const create = (code, getProps) => {
+  const factory = args => new XoError({ ...getProps(args), code })
+  factory.is = (error, predicate) =>
+    error.code === code && iteratee(predicate)(error)
+
+  return factory
+}
+
+// =============================================================================
+
+export const notImplemented = create(0, () => ({
+  message: 'not implemented'
+}))
+
+export const noSuchObject = create(1, (id, type) => ({
+  data: { id, type },
+  message: 'no such object'
+}))
+
+export const unauthorized = create(2, () => ({
+  message: 'not authenticated or not enough permissions'
+}))
+
+export const invalidCredentials = create(3, () => ({
+  message: 'invalid credentials'
+}))
+
+// Deprecated alreadyAuthenticated (4)
+
+export const forbiddenOperation = create(5, (operation, reason) => ({
+  data: { operation, reason },
+  message: `forbidden operation: ${operation}`
+}))
+
+// Deprecated GenericError (6)
+
+export const noHostsAvailable = create(7, () => ({
+  message: 'no hosts available'
+}))
+
+export const authenticationFailed = create(8, () => ({
+  message: 'authentication failed'
+}))
+
+export const serverUnreachable = create(9, objectId => ({
+  data: {
+    objectId
+  },
+  message: 'server unreachable'
+}))
+
+export const invalidParameters = create(10, (message, errors) => {
+  if (isArray(message)) {
+    errors = message
+    message = undefined
+  }
+
+  return {
+    data: { errors },
+    message: message || 'invalid parameters'
+  }
+})
+
+export const vmMissingPvDrivers = create(11, ({ vm }) => ({
+  data: {
+    objectId: vm
+  },
+  message: 'missing PV drivers'
+}))
+
+export const vmIsTemplate = create(12, ({ vm }) => ({
+  data: {
+    objectId: vm
+  },
+  message: 'VM is a template'
+}))
+
+// TODO: We should probably create a more generic error which gathers all incorrect state errors.
+// e.g.:
+// incorrectState {
+//   data: {
+//     objectId: 'af43e227-3deb-4822-a79b-968825de72eb',
+//     property: 'power_state',
+//     actual: 'Running',
+//     expected: 'Halted'
+//   },
+//   message: 'incorrect state'
+// }
+export const vmBadPowerState = create(13, ({ vm, expected, actual }) => ({
+  data: {
+    objectId: vm,
+    expected,
+    actual
+  },
+  message: `VM state is ${actual} but should be ${expected}`
+}))
+
+export const vmLacksFeature = create(14, ({ vm, feature }) => ({
+  data: {
+    objectId: vm,
+    feature
+  },
+  message: `VM lacks feature ${feature || ''}`
+}))
+
+export const notSupportedDuringUpgrade = create(15, () => ({
+  message: 'not supported during upgrade'
+}))
+
+export const objectAlreadyExists = create(16, ({ objectId, objectType }) => ({
+  data: {
+    objectId,
+    objectType
+  },
+  message: `${objectType || 'object'} already exists`
+}))
+
+export const vdiInUse = create(17, ({ vdi, operation }) => ({
+  data: {
+    objectId: vdi,
+    operation
+  },
+  message: 'VDI in use'
+}))
+
+export const hostOffline = create(18, ({ host }) => ({
+  data: {
+    objectId: host
+  },
+  message: 'host offline'
+}))
+
+export const operationBlocked = create(19, ({ objectId, code }) => ({
+  data: {
+    objectId,
+    code
+  },
+  message: 'operation blocked'
+}))
+
+export const patchPrecheckFailed = create(20, ({ errorType, patch }) => ({
+  data: {
+    objectId: patch,
+    errorType
+  },
+  message: `patch precheck failed: ${errorType}`
+}))