diff --git a/cli/package.json b/cli/package.json
index 577cb3ea371b..046ed8d3e6e8 100644
--- a/cli/package.json
+++ b/cli/package.json
@@ -16,6 +16,7 @@
     "check-deps-pre": "npm run check-deps -- --prescript",
     "dtslint": "dtslint types",
     "postinstall": "node ./scripts/post-install.js",
+    "lint": "bin-up eslint --fix *.js scripts/*.js bin/* lib/*.js lib/**/*.js test/*.js test/**/*.js",
     "prerelease": "npm run build",
     "release": "cd build && releaser --no-node --no-changelog",
     "size": "t=\"$(npm pack .)\"; wc -c \"${t}\"; tar tvf \"${t}\"; rm \"${t}\";",
@@ -27,6 +28,7 @@
     "test-unit": "npm run unit",
     "pretest-watch": "npm run check-deps-pre",
     "test-watch": "npm run unit -- --watch",
+    "types": "npm run dtslint",
     "unit": "BLUEBIRD_DEBUG=1 NODE_ENV=test bin-up mocha --reporter mocha-multi-reporters --reporter-options configFile=../mocha-reporter-config.json"
   },
   "dependencies": {
diff --git a/cli/types/index.d.ts b/cli/types/index.d.ts
index 1a08f23bf673..fb2abae383f0 100644
--- a/cli/types/index.d.ts
+++ b/cli/types/index.d.ts
@@ -4304,22 +4304,44 @@ declare namespace Cypress {
   // Diff taken from https://github.com/Microsoft/TypeScript/issues/12215#issuecomment-311923766
   type Diff<T extends string, U extends string> = ({ [P in T]: P } & { [P in U]: never } & { [x: string]: never })[T]
   type Omit<T, K extends keyof T> = Pick<T, Exclude<keyof T, K>>
+
+  /**
+   * Public interface for the global "cy" object. If you want to add
+   * a custom property to this object, you should extend this interface.
+   * @see https://on.cypress.io/typescript#Types-for-custom-commands
+   *
+  ```
+  // in your TS file
+  declare namespace Cypress {
+    interface cy {
+      // declare additional properties on "cy" object, like
+      // label: string
+    }
+    interface Chainable {
+      // declare additional custom commands as methods, like
+      // login(username: string, password: string)
+    }
+  }
+  ```
+   */
+  interface cy extends Chainable<undefined> {}
 }
 
 /**
  * Global variables `cy` added by Cypress with all API commands.
  * @see https://on.cypress.io/api
- * @example
+ *
 ```
 cy.get('button').click()
 cy.get('.result').contains('Expected text')
 ```
  */
-declare const cy: Cypress.Chainable<undefined>
+declare const cy: Cypress.cy
+
 /**
  * Global variable `Cypress` holds common utilities and constants.
  * @see https://on.cypress.io/api
- * @example
+ *
 ```
 Cypress.config("pageLoadTimeout") // => 60000
 Cypress.version // => "1.4.0"
diff --git a/cli/types/tests/plugins-test.ts b/cli/types/tests/plugins-test.ts
new file mode 100644
index 000000000000..b2b06a2db80c
--- /dev/null
+++ b/cli/types/tests/plugins-test.ts
@@ -0,0 +1,58 @@
+//
+// Test that plugin authors can write .d.ts files to extend Cypress types
+// with new "cy" properties and new methods.
+//
+// Unfortunately we cannot test that vendor types located in node_modules are working
+// since those are copied as part of the deploy process
+//
+
+/**
+ * If you want to add additional properties to the "cy" object,
+ * or additional methods to "cy" or "cy.<command>()" chained value,
+ * declare them and TypeScript will merge new definitions with existing ones.
+ * @see https://on.cypress.io/typescript#Types-for-custom-commands
+*/
+declare namespace Cypress {
+  interface cy {
+    /**
+     * We have added a label property to "cy" object.
+     * @example console.log(cy.myLabel)
+    */
+    myLabel: string,
+    /**
+     * Definition for a custom command "login" that was added separately
+     * using `Cypress.Commands.add('login', (username, password) => {...})`.
+     */
+    login(username: string, password: string): Chainable
+  }
+  interface Chainable {
+    /**
+     * Additional property added to the chained object,
+     * returned by Cypress commands. This property will NOT
+     * be part of "cy" object, but a property of an object
+     * returned by Cypress commands.
+    ```
+    cy.get('.element').chainerProp
+    ```
+    */
+    chainerProp: number
+  }
+}
+
+// $ExpectType string
+cy.myLabel
+
+// new custom command "cy.login"
+// $ExpectType Chainable<any>
+cy.login(Cypress.env('username'), Cypress.env('password'))
+
+// "myLabel" property has been added to "interface cy"
+// thus it is NOT of the command chain.
+// $ExpectError
+cy.get('.element').myLabel
+
+// $ExpectType number
+cy.chainerProp
+
+// $ExpectType number
+cy.get('.element').chainerProp