diff --git a/src/index.ts b/src/index.ts
index cb3beec..14130d8 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -3,14 +3,14 @@ if (typeof crypto === 'undefined' || !crypto.subtle)
 
 /**
  * @typedef JwtAlgorithm
- * @type {'ES256'|'ES384'|'ES512'|'HS256'|'HS384'|'HS512'|'RS256'|'RS384'|'RS512'}
+ * @type {'ES256' | 'ES384' | 'ES512' | 'HS256' | 'HS384' | 'HS512' | 'RS256' | 'RS384' | 'RS512'}
  */
-export type JwtAlgorithm = 'ES256'|'ES384'|'ES512'|'HS256'|'HS384'|'HS512'|'RS256'|'RS384'|'RS512'
+export type JwtAlgorithm = 'ES256' | 'ES384' | 'ES512' | 'HS256' | 'HS384' | 'HS512' | 'RS256' | 'RS384' | 'RS512'
 
 /**
  * @typedef JwtAlgorithms
  */
-export interface JwtAlgorithms {
+export type JwtAlgorithms = {
     [key: string]: SubtleCryptoImportKeyAlgorithm
 }
 
@@ -18,16 +18,14 @@ export interface JwtAlgorithms {
  * @typedef JwtHeader
  * @prop {string} [typ] Type
  */
-export interface JwtHeader {
+export type JwtHeader<T = {}> = {
     /**
      * Type (default: `"JWT"`)
      *
      * @default "JWT"
      */
     typ?: string
-
-    [key: string]: any
-}
+} & T
 
 /**
  * @typedef JwtPayload
@@ -39,7 +37,7 @@ export interface JwtHeader {
  * @prop {string} [iat] Issued At
  * @prop {string} [jti] JWT ID
  */
-export interface JwtPayload {
+export type JwtPayload<T = {}> = {
     /** Issuer */
     iss?: string
 
@@ -62,13 +60,13 @@ export interface JwtPayload {
     jti?: string
 
     [key: string]: any
-}
+} & T
 
 /**
  * @typedef JwtOptions
  * @prop {JwtAlgorithm | string} algorithm
  */
-export interface JwtOptions {
+export type JwtOptions = {
     algorithm?: JwtAlgorithm | string
 }
 
@@ -77,32 +75,32 @@ export interface JwtOptions {
  * @extends JwtOptions
  * @prop {JwtHeader} [header]
  */
-export interface JwtSignOptions extends JwtOptions {
+export type JwtSignOptions = {
     header?: JwtHeader
-}
+} & JwtOptions
 
 /**
  * @typedef JwtVerifyOptions
  * @extends JwtOptions
  * @prop {boolean} [throwError=false] If `true` throw error if checks fail. (default: `false`)
  */
-export interface JwtVerifyOptions extends JwtOptions {
+export type JwtVerifyOptions = {
     /**
      * If `true` throw error if checks fail. (default: `false`)
      *
      * @default false
     */
     throwError?: boolean
-}
+} & JwtOptions
 
 /**
  * @typedef JwtData
  * @prop {JwtHeader} header
  * @prop {JwtPayload} payload
  */
-export interface JwtData {
-    header?: JwtHeader
-    payload?: JwtPayload
+export type JwtData<Payload = {}, Header = {}> = {
+    header?: JwtHeader<Header>
+    payload?: JwtPayload<Payload>
 }
 
 const algorithms: JwtAlgorithms = {
@@ -309,10 +307,10 @@ export async function verify(token: string, secret: string | JsonWebKey, options
  * @param {string} token The token string generated by `jwt.sign()`.
  * @returns {JwtData} Returns an `object` containing `header` and `payload`.
  */
-export function decode(token: string): JwtData {
+export function decode<Payload = {}, Header = {}>(token: string): JwtData<Payload, Header> {
     return {
-        header: decodePayload<JwtHeader>(token.split('.')[0].replace(/-/g, '+').replace(/_/g, '/')),
-        payload: decodePayload<JwtPayload>(token.split('.')[1].replace(/-/g, '+').replace(/_/g, '/'))
+        header: decodePayload<JwtHeader<Header>>(token.split('.')[0].replace(/-/g, '+').replace(/_/g, '/')),
+        payload: decodePayload<JwtPayload<Payload>>(token.split('.')[1].replace(/-/g, '+').replace(/_/g, '/'))
     }
 }