diff --git a/README.md b/README.md
index 11a0aa3..c3aedd0 100644
--- a/README.md
+++ b/README.md
@@ -30,7 +30,7 @@ const getToken = async ({
   privateKeyPEM,
   payload,
   alg = 'RS256',
-  cryptoImppl = null,
+  cryptoImpl = null,
   headerAdditions = {},
 }) => { ... }
 ```
@@ -52,7 +52,7 @@ const getTokenFromGCPServiceAccount = async ({
   serviceAccountJSON,
   aud,
   alg = 'RS256',
-  cryptoImppl = null,
+  cryptoImpl = null,
   expiredAfter = 3600,
   headerAdditions = {},
   payloadAdditions = {}
diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..5c27eb1
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,141 @@
+interface HeaderAdditions {
+	/**
+	 * Cryptographic algorithm used to secure the JWT
+	 * @example "RS256"
+	 */
+	alg?: string,
+	/**
+	 * Type of token
+	 * @example "JWT"
+	 */
+	typ?: string,
+	/**
+	 * Service account's private key ID
+	 */
+	kid?: string,
+}
+
+/**
+ * General purpose JWT generation
+ */
+declare function getToken ({
+	privateKeyPEM,
+	payload,
+	alg,
+	headerAdditions,
+	cryptoImpl
+}: {
+	/**
+	 * The private key string in PEM format
+	 */
+	privateKeyPEM: string,
+	payload: {
+			/**
+			 * Service account's email address (sa.client_email)
+			 */
+			iss: string,
+			/**
+			 * Service account's email address (sa.client_email)
+			 */
+			sub: string,
+			/**
+			 * Current Unix timem when the token was issued (in seconds since epoch)
+			 */
+			iat: number,
+			/**
+			 * The time exactly 3600 seconds after the token was issued, when the JWT expires
+			 */
+			exp: number,
+			/**
+			 * The API endpoint.
+			 * @example https://<SERVICE>.googleapis.com/
+			 */
+			aud: string,
+			/**
+			 * The scope of the token
+			 */
+			scope: string
+	},
+	/**
+	 * Cryptographic algorithm used to secure the JWT
+	 * @default "RS256"
+	 */
+	alg?: string,
+	/**
+	 * An object with keys and string values to be added to the header of the JWT.
+	 */
+	headerAdditions?: HeaderAdditions,
+	/**
+	 * The crypto implementation to use. Use `null` to use the default implementation.
+	 * @see https://w3c.github.io/webcrypto/#crypto-interface
+	 * @default null
+	 */
+	cryptoImpl?: Crypto
+}): Promise<string>
+
+/**
+ * Generate a JWT from a service account JSON
+ */
+declare function getTokenFromGCPServiceAccount ({
+		serviceAccountJSON,
+		aud,
+		alg,
+		cryptoImpl,
+		headerAdditions,
+		payloadAdditions
+}: {
+	/**
+	 * Structure of a service account JSON
+	 */
+	serviceAccountJSON: {
+		type: string;
+		project_id: string;
+		private_key_id: string;
+		private_key: string;
+		client_email: string;
+		client_id: string;
+		auth_uri: string;
+		token_uri: string;
+		auth_provider_x509_cert_url: string;
+		client_x509_cert_url: string;
+	},
+	/**
+	 * The API endpoint.
+	 * @example https://<SERVICE>.googleapis.com/
+	 */
+	aud: string,
+	/**
+	 * Cryptographic algorithm used to secure the JWT
+	 * @default "RS256"
+	 */
+	alg?: string,
+	/**
+	 * The crypto implementation to use. Use `null` to use the default implementation.
+	 * @see https://w3c.github.io/webcrypto/#crypto-interface
+	 * @default null
+	 */
+	cryptoImpl?: Crypto,
+	/**
+	 * The time in seconds after the token was issued when the JWT expires
+	 * @default 3600
+	 */
+	expiredAfter?: number,
+	/**
+	 * An object with keys and string values to be added to the header of the JWT.
+	 */
+	headerAdditions?: HeaderAdditions,
+	/**
+	 * an object with keys and string values to be added to the payload of the JWT.
+	 * @example { scope: 'https://www.googleapis.com/auth/chat.bot' }
+	 */
+	payloadAdditions?: Record<string, any>
+}): Promise<string>
+
+export { getTokenFromGCPServiceAccount, getToken }
+
+interface commonjsModule {
+	getTokenFromGCPServiceAccount,
+	getToken
+}
+
+export default commonjsModule;
diff --git a/package.json b/package.json
index 55d5d99..e8012ba 100644
--- a/package.json
+++ b/package.json
@@ -5,6 +5,8 @@
   "author": "Sagi Kedmi <git@sagi.io> (https://sagi.io)",
   "homepage": "https://sagi.io",
   "main": "index.js",
+  "type": "commonjs",
+  "types": "index.d.ts",
   "license": "MIT",
   "private": false,
   "scripts": {