diff --git a/packages/@uppy/companion-client/src/AuthError.js b/packages/@uppy/companion-client/src/AuthError.ts
similarity index 87%
rename from packages/@uppy/companion-client/src/AuthError.js
rename to packages/@uppy/companion-client/src/AuthError.ts
index 14517d3400..3bd743091f 100644
--- a/packages/@uppy/companion-client/src/AuthError.js
+++ b/packages/@uppy/companion-client/src/AuthError.ts
@@ -1,6 +1,8 @@
 'use strict'
 
 class AuthError extends Error {
+  public isAuthError: true
+
   constructor () {
     super('Authorization required')
     this.name = 'AuthError'
diff --git a/packages/@uppy/companion-client/src/Provider.js b/packages/@uppy/companion-client/src/Provider.ts
similarity index 93%
rename from packages/@uppy/companion-client/src/Provider.js
rename to packages/@uppy/companion-client/src/Provider.ts
index 28a7a38f71..8f2d10efa7 100644
--- a/packages/@uppy/companion-client/src/Provider.js
+++ b/packages/@uppy/companion-client/src/Provider.ts
@@ -1,18 +1,18 @@
 'use strict'
 
-import RequestClient from './RequestClient.js'
-import * as tokenStorage from './tokenStorage.js'
+import RequestClient from './RequestClient.ts'
+import * as tokenStorage from './tokenStorage.ts'
 
-const getName = (id) => {
+const getName = (id: string): string => {
   return id.split('-').map((s) => s.charAt(0).toUpperCase() + s.slice(1)).join(' ')
 }
 
-function getOrigin () {
+function getOrigin (): Location['origin'] {
   // eslint-disable-next-line no-restricted-globals
   return location.origin
 }
 
-function getRegex (value) {
+function getRegex (value: unknown): RegExp | undefined {
   if (typeof value === 'string') {
     return new RegExp(`^${value}$`)
   } if (value instanceof RegExp) {
@@ -21,14 +21,14 @@ function getRegex (value) {
   return undefined
 }
 
-function isOriginAllowed (origin, allowedOrigin) {
+function isOriginAllowed (origin: Location['origin'], allowedOrigin: unknown): boolean {
   const patterns = Array.isArray(allowedOrigin) ? allowedOrigin.map(getRegex) : [getRegex(allowedOrigin)]
   return patterns
     .some((pattern) => pattern?.test(origin) || pattern?.test(`${origin}/`)) // allowing for trailing '/'
 }
 
 export default class Provider extends RequestClient {
-  #refreshingTokenPromise
+  #refreshingTokenPromise: Promise<void>
 
   constructor (uppy, opts) {
     super(uppy, opts)
@@ -41,9 +41,9 @@ export default class Provider extends RequestClient {
     this.preAuthToken = null
   }
 
-  async headers () {
+  async headers (): Promise<Record<string, string>> {
     const [headers, token] = await Promise.all([super.headers(), this.#getAuthToken()])
-    const authHeaders = {}
+    const authHeaders: Record<string, string> = { __proto__: null as unknown as string }
     if (token) {
       authHeaders['uppy-auth-token'] = token
     }
@@ -56,7 +56,7 @@ export default class Provider extends RequestClient {
     return { ...headers, ...authHeaders }
   }
 
-  onReceiveResponse (response) {
+  onReceiveResponse (response: Response) {
     super.onReceiveResponse(response)
     const plugin = this.uppy.getPlugin(this.pluginId)
     const oldAuthenticated = plugin.getPluginState().authenticated
@@ -158,7 +158,7 @@ export default class Provider extends RequestClient {
   async request (...args) {
     await this.#refreshingTokenPromise
 
-    try {
+    try{
       // to test simulate access token expired (leading to a token token refresh),
       // see mockAccessTokenExpiredError in companion/drive.
       // If you want to test refresh token *and* access token invalid, do this for example with Google Drive:
diff --git a/packages/@uppy/companion-client/src/RequestClient.test.js b/packages/@uppy/companion-client/src/RequestClient.test.ts
similarity index 91%
rename from packages/@uppy/companion-client/src/RequestClient.test.js
rename to packages/@uppy/companion-client/src/RequestClient.test.ts
index b1817827c5..c14d0d7aef 100644
--- a/packages/@uppy/companion-client/src/RequestClient.test.js
+++ b/packages/@uppy/companion-client/src/RequestClient.test.ts
@@ -1,5 +1,5 @@
 import { describe, it, expect } from 'vitest'
-import RequestClient from './RequestClient.js'
+import RequestClient from './RequestClient.ts'
 
 describe('RequestClient', () => {
   it('has a hostname without trailing slash', () => {
diff --git a/packages/@uppy/companion-client/src/RequestClient.js b/packages/@uppy/companion-client/src/RequestClient.ts
similarity index 91%
rename from packages/@uppy/companion-client/src/RequestClient.js
rename to packages/@uppy/companion-client/src/RequestClient.ts
index ffaac2fd28..cdcab28c25 100644
--- a/packages/@uppy/companion-client/src/RequestClient.js
+++ b/packages/@uppy/companion-client/src/RequestClient.ts
@@ -8,12 +8,15 @@ import ErrorWithCause from '@uppy/utils/lib/ErrorWithCause'
 import emitSocketProgress from '@uppy/utils/lib/emitSocketProgress'
 import getSocketHost from '@uppy/utils/lib/getSocketHost'
 
-import AuthError from './AuthError.js'
-
+import AuthError from './AuthError.ts'
+// eslint-disable-next-line @typescript-eslint/ban-ts-comment
+// @ts-ignore We don't want TS to generate types for the package.json
 import packageJson from '../package.json'
 
-// Remove the trailing slash so we can always safely append /xyz.
-function stripSlash (url) {
+/**
+ * Removes the trailing slash so we can always safely append /xyz.
+ */
+function stripSlash (url: string): string {
   return url.replace(/\/$/, '')
 }
 
@@ -23,15 +26,15 @@ const socketActivityTimeoutMs = 5 * 60 * 1000 // set to a low number like 10000
 const authErrorStatusCode = 401
 
 class HttpError extends Error {
-  statusCode
+  public statusCode: number
 
-  constructor({ statusCode, message }) {
+  constructor({ statusCode, message }: { statusCode: number, message: string}) {
     super(message)
     this.statusCode = statusCode
   }
 }
 
-async function handleJSONResponse (res) {
+async function handleJSONResponse (res: Response): Promise<ReturnType<typeof JSON.parse>> {
   if (res.status === authErrorStatusCode) {
     throw new AuthError()
   }
@@ -61,7 +64,7 @@ const allowedHeadersCache = new Map()
 export default class RequestClient {
   static VERSION = packageJson.version
 
-  #companionHeaders
+  #companionHeaders: Record<string, string>
 
   constructor (uppy, opts) {
     this.uppy = uppy
@@ -70,21 +73,21 @@ export default class RequestClient {
     this.#companionHeaders = opts?.companionHeaders
   }
 
-  setCompanionHeaders (headers) {
+  setCompanionHeaders (headers: Record<string, string>): void {
     this.#companionHeaders = headers
   }
 
-  [Symbol.for('uppy test: getCompanionHeaders')] () {
+  private [Symbol.for('uppy test: getCompanionHeaders')] (): Record<string, string> {
     return this.#companionHeaders
   }
 
-  get hostname () {
+  get hostname (): string {
     const { companion } = this.uppy.getState()
     const host = this.opts.companionUrl
     return stripSlash(companion && companion[host] ? companion[host] : host)
   }
 
-  async headers () {
+  async headers (): Promise<Record<string, string>> {
     const defaultHeaders = {
       Accept: 'application/json',
       'Content-Type': 'application/json',
@@ -97,7 +100,7 @@ export default class RequestClient {
     }
   }
 
-  onReceiveResponse ({ headers }) {
+  onReceiveResponse ({ headers }: Response): void {
     const state = this.uppy.getState()
     const companion = state.companion || {}
     const host = this.opts.companionUrl
@@ -110,7 +113,7 @@ export default class RequestClient {
     }
   }
 
-  #getUrl (url) {
+  #getUrl (url: string): string {
     if (/^(https?:|)\/\//.test(url)) {
       return url
     }
@@ -131,7 +134,7 @@ export default class RequestClient {
     Subsequent requests use the cached result of the preflight.
     However if there is an error retrieving the allowed headers, we will try again next time
   */
-  async preflight (path) {
+  async preflight (path: string): Promise<string[]>{
     const allowedHeadersCached = allowedHeadersCache.get(this.hostname)
     if (allowedHeadersCached != null) return allowedHeadersCached
 
@@ -141,7 +144,7 @@ export default class RequestClient {
       'uppy-auth-token',
     ]
 
-    const promise = (async () => {
+    const promise = (async (): Promise<string[]> => {
       try {
         const response = await fetch(this.#getUrl(path), { method: 'OPTIONS' })
 
@@ -176,7 +179,7 @@ export default class RequestClient {
     return promise
   }
 
-  async preflightAndHeaders (path) {
+  async preflightAndHeaders (path:string):Record<string,string> {
     const [allowedHeaders, headers] = await Promise.all([
       this.preflight(path),
       this.headers(),
@@ -195,8 +198,7 @@ export default class RequestClient {
     )
   }
 
-  /** @protected */
-  async request ({ path, method = 'GET', data, skipPostResponse, signal }) {
+protected async request ({ path, method = 'GET', data, skipPostResponse, signal }): ReturnType<typeof handleJSONResponse> {
     try {
       const headers = await this.preflightAndHeaders(path)
       const response = await fetchWithNetworkError(this.#getUrl(path), {
@@ -219,21 +221,21 @@ export default class RequestClient {
     }
   }
 
-  async get (path, options = undefined) {
+  async get (path, options = undefined): ReturnType<typeof handleJSONResponse> {
     // TODO: remove boolean support for options that was added for backward compatibility.
     // eslint-disable-next-line no-param-reassign
     if (typeof options === 'boolean') options = { skipPostResponse: options }
     return this.request({ ...options, path })
   }
 
-  async post (path, data, options = undefined) {
+  async post (path, data, options = undefined): ReturnType<typeof handleJSONResponse> {
     // TODO: remove boolean support for options that was added for backward compatibility.
     // eslint-disable-next-line no-param-reassign
     if (typeof options === 'boolean') options = { skipPostResponse: options }
     return this.request({ ...options, path, method: 'POST', data })
   }
 
-  async delete (path, data = undefined, options) {
+  async delete (path, data = undefined, options): ReturnType<typeof handleJSONResponse> {
     // TODO: remove boolean support for options that was added for backward compatibility.
     // eslint-disable-next-line no-param-reassign
     if (typeof options === 'boolean') options = { skipPostResponse: options }
@@ -312,7 +314,7 @@ export default class RequestClient {
     }
   }
 
-  #requestSocketToken = async ({ file, postBody, signal }) => {
+  #requestSocketToken = async ({ file, postBody, signal }): Promise<string> => {
     if (file.remote.url == null) {
       throw new Error('Cannot connect to an undefined URL')
     }
@@ -329,10 +331,8 @@ export default class RequestClient {
    * This method will ensure a websocket for the specified file and returns a promise that resolves
    * when the file has finished downloading, or rejects if it fails.
    * It will retry if the websocket gets disconnected
-   * 
-   * @param {{ file: UppyFile, queue: RateLimitedQueue, signal: AbortSignal }} file
    */
-  async #awaitRemoteFileUpload ({ file, queue, signal }) {
+  async #awaitRemoteFileUpload ({ file, queue, signal }: { file: UppyFile, queue: RateLimitedQueue, signal?: AbortSignal }): Promise<void> {
     let removeEventHandlers
 
     const { capabilities } = this.uppy.getState()
diff --git a/packages/@uppy/companion-client/src/SearchProvider.js b/packages/@uppy/companion-client/src/SearchProvider.ts
similarity index 72%
rename from packages/@uppy/companion-client/src/SearchProvider.js
rename to packages/@uppy/companion-client/src/SearchProvider.ts
index 19bc051d74..0ab41adfa3 100644
--- a/packages/@uppy/companion-client/src/SearchProvider.js
+++ b/packages/@uppy/companion-client/src/SearchProvider.ts
@@ -1,12 +1,14 @@
 'use strict'
 
-import RequestClient from './RequestClient.js'
+import RequestClient from './RequestClient.ts'
 
-const getName = (id) => {
+const getName = (id: string) : string=> {
   return id.split('-').map((s) => s.charAt(0).toUpperCase() + s.slice(1)).join(' ')
 }
 
 export default class SearchProvider extends RequestClient {
+  public id: string
+
   constructor (uppy, opts) {
     super(uppy, opts)
     this.provider = opts.provider
@@ -15,11 +17,11 @@ export default class SearchProvider extends RequestClient {
     this.pluginId = this.opts.pluginId
   }
 
-  fileUrl (id) {
+  fileUrl (id: string): string {
     return `${this.hostname}/search/${this.id}/get/${id}`
   }
 
-  search (text, queries) {
+  search (text: string, queries?: string): Promise<unknown[]> {
     return this.get(`search/${this.id}/list?q=${encodeURIComponent(text)}${queries ? `&${queries}` : ''}`)
   }
 }
diff --git a/packages/@uppy/companion-client/src/index.js b/packages/@uppy/companion-client/src/index.js
deleted file mode 100644
index 6dc7cb19e0..0000000000
--- a/packages/@uppy/companion-client/src/index.js
+++ /dev/null
@@ -1,9 +0,0 @@
-'use strict'
-
-/**
- * Manages communications with Companion
- */
-
-export { default as RequestClient } from './RequestClient.js'
-export { default as Provider } from './Provider.js'
-export { default as SearchProvider } from './SearchProvider.js'
diff --git a/packages/@uppy/companion-client/src/index.ts b/packages/@uppy/companion-client/src/index.ts
new file mode 100644
index 0000000000..c347daaf88
--- /dev/null
+++ b/packages/@uppy/companion-client/src/index.ts
@@ -0,0 +1,7 @@
+/**
+ * Manages communications with Companion
+ */
+
+export { default as RequestClient } from './RequestClient.ts'
+export { default as Provider } from './Provider.ts'
+export { default as SearchProvider } from './SearchProvider.ts'
diff --git a/packages/@uppy/companion-client/src/tokenStorage.js b/packages/@uppy/companion-client/src/tokenStorage.ts
similarity index 50%
rename from packages/@uppy/companion-client/src/tokenStorage.js
rename to packages/@uppy/companion-client/src/tokenStorage.ts
index 2bfc9f5873..e16816246e 100644
--- a/packages/@uppy/companion-client/src/tokenStorage.js
+++ b/packages/@uppy/companion-client/src/tokenStorage.ts
@@ -3,18 +3,18 @@
 /**
  * This module serves as an Async wrapper for LocalStorage
  */
-export function setItem (key, value) {
+export function setItem (key: Parameters<Storage['setItem']>[0], value:Parameters<Storage['setItem']>[1]): Promise<void> {
   return new Promise((resolve) => {
     localStorage.setItem(key, value)
     resolve()
   })
 }
 
-export function getItem (key) {
+export function getItem (key: Parameters<Storage['getItem']>[0]): Promise<ReturnType<Storage['getItem']>> {
   return Promise.resolve(localStorage.getItem(key))
 }
 
-export function removeItem (key) {
+export function removeItem (key: Parameters<Storage['removeItem']>[0]): Promise<void> {
   return new Promise((resolve) => {
     localStorage.removeItem(key)
     resolve()
diff --git a/packages/@uppy/companion-client/tsconfig.build.json b/packages/@uppy/companion-client/tsconfig.build.json
new file mode 100644
index 0000000000..97515c01f2
--- /dev/null
+++ b/packages/@uppy/companion-client/tsconfig.build.json
@@ -0,0 +1,21 @@
+{
+  "extends": "../../../tsconfig.shared",
+  "compilerOptions": {
+    "outDir": "./lib",
+    "rootDir": "./src",
+    "resolveJsonModule": false,
+    "noImplicitAny": false,
+    "skipLibCheck": true
+  },
+  "include": [
+    "./src/**/*.*"
+  ],
+  "exclude": [
+    "./src/**/*.test.ts"
+  ],
+  "references": [
+    {
+      "path": "../utils/tsconfig.build.json"
+    }
+  ]
+}
diff --git a/packages/@uppy/companion-client/tsconfig.json b/packages/@uppy/companion-client/tsconfig.json
new file mode 100644
index 0000000000..1c179363de
--- /dev/null
+++ b/packages/@uppy/companion-client/tsconfig.json
@@ -0,0 +1,16 @@
+{
+  "extends": "../../../tsconfig.shared",
+  "compilerOptions": {
+    "emitDeclarationOnly": false,
+    "noEmit": true
+  },
+  "include": [
+    "./package.json",
+    "./src/**/*.*"
+  ],
+  "references": [
+    {
+      "path": "../utils/tsconfig.build.json"
+    }
+  ]
+}