diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..f603626
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,38 @@
+/**
+ * encode a string to base64
+ *
+ * @param {string} str string to encode
+ * @param {string} encoding encoding the string is in
+ * @returns {string} base64
+ */
+export function to_b64(str: string, encoding?: string): string;
+/**
+ * encode a string to hex
+ *
+ * @param {string} str string to encode
+ * @param {string} encoding encoding the string is in
+ * @returns {string} hex
+ */
+export function to_hex(str: string, encoding?: string): string;
+/**
+ * encode a string to utf-8
+ *
+ * @param {string} str string to encode
+ * @param {string} encoding encoding the string is in
+ * @returns {string} utf-8
+ */
+export function to_utf8(str: string, encoding: string): string;
+/**
+ * encode a number to hex
+ *
+ * @param {number} n number to encode
+ * @returns {string} hex
+ */
+export function num_to_hex(n: number): string;
+/**
+ * decode a number from hex
+ *
+ * @param {string} h hex to decode
+ * @returns {number} number
+ */
+export function hex_to_num(h: string): number;
diff --git a/index.js b/index.js
index feb444e..5e55f77 100644
--- a/index.js
+++ b/index.js
@@ -44,9 +44,31 @@ function to_hex (str, encoding = '') {
   return buf.toString ('hex');
 }
 
+/**
+ * encode a number to hex
+ *
+ * @param {number} n number to encode
+ * @returns {string} hex
+ */
+function num_to_hex (n) {
+  return n.toString(16);
+}
+
+/**
+ * decode a number from hex
+ *
+ * @param {string} h hex to decode
+ * @returns {number} number
+ */
+function hex_to_num (h) {
+  return parseInt(h, 16);
+}
+
 module.exports = {
   to_b64,
   to_hex,
-  to_utf8
+  to_utf8,
+  num_to_hex,
+  hex_to_num
 };