diff --git a/.eslintignore b/.eslintignore
index 4c9f00119b..dd4f092fa0 100644
--- a/.eslintignore
+++ b/.eslintignore
@@ -3,3 +3,4 @@
 /node_modules
 /dist
 **/build/**
+/test/cypress
diff --git a/lib/api.ts b/lib/api.ts
index 194748200f..58dac56ab6 100644
--- a/lib/api.ts
+++ b/lib/api.ts
@@ -8,7 +8,7 @@ import createEditor from './editor'
 import createNavigator from './navigator'
 import createApp from './app'
 import locations from './locations'
-import { BaseExtensionSDK, EntryFieldInfo, FieldInfo, NavigatorAPI, KnownSDK } from './types'
+import { BaseExtensionSDK, EntryFieldInfo, NavigatorAPI, KnownSDK, ConnectMessage } from './types'
 import { Channel } from './channel'
 
 const DEFAULT_API_PRODUCERS = [
@@ -19,8 +19,8 @@ const DEFAULT_API_PRODUCERS = [
   makeWindowAPI
 ]
 
-type producerFunc = (channel: Channel, data: any, currentWindow: Window) => any
-const LOCATION_TO_API_PRODUCERS: { [location: string]: producerFunc[] } = {
+type ProducerFunc = (channel: Channel, data: ConnectMessage, currentWindow: Window) => any
+const LOCATION_TO_API_PRODUCERS: { [location: string]: ProducerFunc[] } = {
   [locations.LOCATION_ENTRY_FIELD]: DEFAULT_API_PRODUCERS,
   [locations.LOCATION_ENTRY_FIELD_SIDEBAR]: DEFAULT_API_PRODUCERS,
   [locations.LOCATION_ENTRY_SIDEBAR]: [makeSharedAPI, makeEntryAPI, makeEditorAPI, makeWindowAPI],
@@ -30,9 +30,11 @@ const LOCATION_TO_API_PRODUCERS: { [location: string]: producerFunc[] } = {
   [locations.LOCATION_APP_CONFIG]: [makeSharedAPI, makeAppAPI]
 }
 
-// TODO Remove any once we know payload
-// TODO data is directly received through event passthrough
-export default function createAPI(channel: Channel, data: any, currentWindow: Window): KnownSDK {
+export default function createAPI(
+  channel: Channel,
+  data: ConnectMessage,
+  currentWindow: Window
+): KnownSDK {
   const producers = LOCATION_TO_API_PRODUCERS[data.location as string] || DEFAULT_API_PRODUCERS
 
   return producers.reduce((api, produce) => {
@@ -40,7 +42,7 @@ export default function createAPI(channel: Channel, data: any, currentWindow: Wi
   }, {}) as any
 }
 
-function makeSharedAPI(channel: Channel, data: any): BaseExtensionSDK {
+function makeSharedAPI(channel: Channel, data: ConnectMessage): BaseExtensionSDK {
   const { user, parameters, locales, ids, initialContentTypes } = data
   const currentLocation = data.location || locations.LOCATION_ENTRY_FIELD
 
@@ -89,12 +91,7 @@ function makeEditorAPI(channel: Channel, data: any) {
 
 function makeEntryAPI(
   channel: Channel,
-  {
-    locales,
-    contentType,
-    entry,
-    fieldInfo
-  }: { locales: any; contentType: string; entry: any; fieldInfo: any }
+  { locales, contentType, entry, fieldInfo }: ConnectMessage
 ) {
   const createEntryField = (info: EntryFieldInfo) => new Field(channel, info, locales.default)
 
@@ -104,7 +101,10 @@ function makeEntryAPI(
   }
 }
 
-function makeFieldAPI(channel: Channel, { field }: { field: FieldInfo }) {
+function makeFieldAPI(channel: Channel, { field }: ConnectMessage) {
+  if (!field) {
+    throw new Error('FieldAPI called for location without "field" property defined.')
+  }
   return {
     field: new FieldLocale(channel, field)
   }
diff --git a/lib/channel.ts b/lib/channel.ts
index 783b9ec348..a7477098a9 100644
--- a/lib/channel.ts
+++ b/lib/channel.ts
@@ -1,12 +1,11 @@
 import { Signal } from './signal'
+import { ConnectMessage } from './types'
 
-// TODO derive arg1 and arg2 shape of onConnect callback
-// TODO Both come through initial event.data over Channel
 export default function connect(
   currentWindow: Window,
-  onConnect: (arg1: Channel, args2: any, arg3: any) => void
+  onConnect: (channel: Channel, message: ConnectMessage, messageQueue: unknown[]) => void
 ) {
-  waitForConnect(currentWindow, (params: any, messageQueue: any) => {
+  waitForConnect(currentWindow, (params: ConnectMessage, messageQueue: unknown[]) => {
     const channel = new Channel(params.id, currentWindow)
     onConnect(channel, params, messageQueue)
   })
diff --git a/lib/editor.ts b/lib/editor.ts
index 2e95e666d9..8c7ec79e49 100644
--- a/lib/editor.ts
+++ b/lib/editor.ts
@@ -1,4 +1,4 @@
-import { EditorInterface } from '../typings'
+import { EditorInterface, EditorLocaleSettings } from './types'
 import { Channel } from './channel'
 import { MemoizedSignal } from './signal'
 
@@ -6,8 +6,7 @@ export default function createEditor(channel: Channel, editorInterface: EditorIn
   const _localeSettingsSygnal = new MemoizedSignal(undefined)
   const _showDisabledFieldsSygnal = new MemoizedSignal(undefined)
 
-  // TODO any
-  channel.addHandler('localeSettingsChanged', (settings: any) => {
+  channel.addHandler('localeSettingsChanged', (settings: EditorLocaleSettings) => {
     _localeSettingsSygnal.dispatch(settings)
   })
 
diff --git a/lib/field.ts b/lib/field.ts
index de6059abb0..caa52e02a2 100644
--- a/lib/field.ts
+++ b/lib/field.ts
@@ -54,8 +54,7 @@ export default class Field implements EntryFieldAPI {
     return this.setValue(undefined, locale)
   }
 
-  // TODO maybe swap argument positions to get rid of swap logic
-  onValueChanged(locale: string | Function, handler?: Function) {
+  onValueChanged(locale: string | ((value: any) => void), handler?: (value: any) => void) {
     const h = handler || locale
     if (!handler) {
       locale = ''
@@ -63,8 +62,10 @@ export default class Field implements EntryFieldAPI {
     return this._getFieldLocale(locale as string).onValueChanged(h as any)
   }
 
-  // TODO maybe swap argument positions to get rid of swap logic
-  onIsDisabledChanged(locale: string | Function, handler?: Function) {
+  onIsDisabledChanged(
+    locale: string | ((isDisabled: boolean) => void),
+    handler?: (isDisabled: boolean) => void
+  ) {
     const h = handler || locale
     if (!handler) {
       locale = ''
diff --git a/lib/initialize.ts b/lib/initialize.ts
index fdf8a3c784..e4f54dbff6 100644
--- a/lib/initialize.ts
+++ b/lib/initialize.ts
@@ -1,10 +1,10 @@
-import { KnownSDK } from './types'
+import { ConnectMessage, KnownSDK } from './types'
 import connect, { Channel } from './channel'
 
 export default function createInitializer(
   currentWindow: Window,
-  apiCreator: (channel: Channel, data: any, window: Window) => KnownSDK
-): <T extends KnownSDK = KnownSDK>(initCallback: (sdk: T) => any) => void {
+  apiCreator: (channel: Channel, data: ConnectMessage, window: Window) => KnownSDK
+) {
   const connectDeferred = createDeferred()
 
   connectDeferred.promise.then(([channel]: [Channel]) => {
@@ -20,29 +20,32 @@ export default function createInitializer(
     (...args) => connectDeferred.resolve(args)
   )
 
-  // TODO Replace sdk/customSdk [any] with api and customApi types
-  return function init(initCb: (sdk: any, customSdk: any) => any, { makeCustomApi = null } = {}) {
-    connectDeferred.promise.then(([channel, params, messageQueue]: [Channel, any, any]) => {
-      const api = apiCreator(channel, params, currentWindow)
+  return function init(
+    initCb: (sdk: KnownSDK, customSdk: any) => any,
+    { makeCustomApi = null } = {}
+  ) {
+    connectDeferred.promise.then(
+      ([channel, params, messageQueue]: [Channel, ConnectMessage, unknown[]]) => {
+        const api = apiCreator(channel, params, currentWindow)
 
-      let customApi
-      if (typeof makeCustomApi === 'function') {
-        // Reason for the typecast: https://github.com/microsoft/TypeScript/issues/14889
-        customApi = (makeCustomApi as any)(channel, params)
-      }
+        let customApi
+        if (typeof makeCustomApi === 'function') {
+          // Reason for the typecast: https://github.com/microsoft/TypeScript/issues/14889
+          customApi = (makeCustomApi as any)(channel, params)
+        }
+
+        // Handle pending incoming messages.
+        // APIs are created before so handlers are already
+        // registered on the channel.
+        messageQueue.forEach(m => {
+          // TODO Expose private handleMessage method
+          ;(channel as any)._handleMessage(m)
+        })
 
-      // Handle pending incoming messages.
-      // APIs are created before so handlers are already
-      // registered on the channel.
-      // TODO message has "id" or "method" attribute defined
-      messageQueue.forEach((m: any) => {
-        // TODO Expose private handleMessage method
-        ;(channel as any)._handleMessage(m)
-      })
-
-      // Hand over control to the developer.
-      initCb(api, customApi)
-    })
+        // Hand over control to the developer.
+        initCb(api, customApi)
+      }
+    )
   }
 }
 
diff --git a/lib/space.ts b/lib/space.ts
index 9b379157b5..186709ec10 100644
--- a/lib/space.ts
+++ b/lib/space.ts
@@ -1,6 +1,5 @@
-import { ContentType } from '../typings'
+import { ContentType, SpaceAPI } from './types'
 import { Channel } from './channel'
-import { SpaceAPI } from './types'
 
 const spaceMethods: Array<keyof SpaceAPI> = [
   'getContentType',
diff --git a/lib/types.ts b/lib/types.ts
index 7661bda008..5ffe57cbb2 100644
--- a/lib/types.ts
+++ b/lib/types.ts
@@ -75,6 +75,24 @@ export interface EntryFieldInfo {
   values: { [locale: string]: any }
 }
 
+export interface ConnectMessage {
+  id: string
+  location: Location[keyof Location]
+  parameters: ParametersAPI
+  locales: LocalesAPI
+  user: User
+  initialContentTypes: ContentType[]
+  ids: IdsAPI
+  contentType: ContentType
+  editorInterface?: EditorInterface
+  entry: {
+    sys: EntrySys
+    metadata?: any
+  }
+  fieldInfo: EntryFieldInfo[]
+  field?: FieldInfo
+}
+
 /* Field API */
 export interface FieldAPI {
   /** The ID of a field is defined in an entry's content type. */
@@ -569,16 +587,16 @@ export interface IdsAPI {
   contentType: string
 }
 
+export interface EditorLocaleSettings {
+  mode: 'multi' | 'single'
+  focused?: string
+  active?: Array<string>
+}
+
 export interface SharedEditorSDK {
   editor: {
     editorInterface: EditorInterface
-    onLocaleSettingsChanged: (
-      callback: (value: {
-        mode: 'multi' | 'single'
-        focused?: string
-        active?: Array<string>
-      }) => any
-    ) => Function
+    onLocaleSettingsChanged: (callback: (value: EditorLocaleSettings) => any) => Function
     onShowDisabledFieldsChanged: (callback: (value: boolean) => any) => Function
   }
   /** Allows to read and update the value of any field of the current entry and to get the entry's metadata */
diff --git a/package.json b/package.json
index f2ebc039b9..da10407a95 100644
--- a/package.json
+++ b/package.json
@@ -13,8 +13,8 @@
   ],
   "scripts": {
     "test": "ts-mocha 'test/unit/*.[jt]s'",
-    "lint": "tsc -b && eslint '{lib,test}/**/*.{t,j}s'",
-    "lint:fix": "eslint --fix lib/ test/",
+    "lint": "eslint '{lib,test}/**/*.{t,j}s'",
+    "lint:fix": "npm run lint -- --fix",
     "build": "npm run typings && rollup -c --compact",
     "build:debug": "npm run build -- --sourcemap",
     "typings": "tsc -b typings.tsconfig.json && mv lib/types.d.ts typings.d.ts && cat module-declaration.d.ts >> typings.d.ts",
diff --git a/test/unit/api.spec.ts b/test/unit/api.spec.ts
index 3888e31817..bc6d93d21b 100644
--- a/test/unit/api.spec.ts
+++ b/test/unit/api.spec.ts
@@ -2,6 +2,7 @@ import { makeDOM, mockMutationObserver, expect } from '../helpers'
 
 import createAPI from '../../lib/api'
 import locations from '../../lib/locations'
+import { AppExtensionSDK, ConnectMessage } from '../../lib/types'
 
 const sharedExpected = [
   'location',
@@ -19,7 +20,7 @@ const sharedExpected = [
 function test(expected: string[], location: string | undefined, expectedLocation = location) {
   const channel = { addHandler: () => {} } as any
 
-  const data = {
+  const data = ({
     location,
     user: 'USER',
     parameters: 'PARAMS',
@@ -45,7 +46,7 @@ function test(expected: string[], location: string | undefined, expectedLocation
     ids: {
       extension: 'my-test-id'
     }
-  }
+  } as unknown) as ConnectMessage
 
   const dom = makeDOM()
   mockMutationObserver(dom, () => {})
@@ -110,10 +111,9 @@ describe('createAPI()', () => {
   it('returns correct shape of the app API (app)', () => {
     const expected = ['app']
 
-    const api = test(expected, locations.LOCATION_APP_CONFIG)
+    const api = (test(expected, locations.LOCATION_APP_CONFIG) as unknown) as AppExtensionSDK
 
-    // TODO app not on this object?
-    expect((api as any).app).to.have.all.keys([
+    expect(api.app).to.have.all.keys([
       'setReady',
       'isInstalled',
       'getParameters',