diff --git a/main.test.ts b/main.test.ts
index febdc96..85d3738 100644
--- a/main.test.ts
+++ b/main.test.ts
@@ -3,26 +3,23 @@ import { assertEquals } from 'https://deno.land/std@0.154.0/testing/asserts.ts';
 import { Event, EventConfig, Calendar } from './mod.ts';
 import { short_utc } from './date.ts';
 
-Deno.test('UTC event',
-  () => {
-    const cfg: EventConfig = {
-      title: 'test',
-      beginDate: [2022, 8, 1, 10, 10],
-      endDate: [2022, 8, 1, 11, 10],
-      desc: 'Hello',
-      zone: 'utc' // Universal time required
-    };
-    const evt = new Event(cfg);
-    const lines = evt.toLines()
-    assertEquals(lines[0][0], "BEGIN")
-    assertEquals(lines[0][1], "VEVENT")
+Deno.test('UTC event', () => {
+  const cfg: EventConfig = {
+    title: 'test',
+    beginDate: [2022, 8, 1, 10, 10],
+    endDate: [2022, 8, 1, 11, 10],
+    desc: 'Hello',
+    zone: 'utc', // Universal time required
+  };
+  const evt = new Event(cfg);
+  const lines = evt.toLines();
+  assertEquals(lines[0][0], 'BEGIN');
+  assertEquals(lines[0][1], 'VEVENT');
 
-    // Note 'Z' suffix for UTC (precaution against daylight saving time surprises)
-    assertEquals(lines[3], ["DTSTART", "20220801T101000Z"])
-    assertEquals(lines[4], ["DTEND", "20220801T111000Z"]) 
-
-  },
-);
+  // Note 'Z' suffix for UTC (precaution against daylight saving time surprises)
+  assertEquals(lines[3], ['DTSTART', '20220801T101000Z']);
+  assertEquals(lines[4], ['DTEND', '20220801T111000Z']);
+});
 
 Deno.test({
   name: 'calendar',
@@ -49,11 +46,11 @@ Deno.test({
       desc: 'Implement a module to generate .ics files',
       organizer: {
         name: 'Sam Worthington',
-        email: 'sam@dev.com'
+        email: 'sam@dev.com',
       },
       url: 'https://www.google.com/',
       location: 'ABC Tank Warehouse',
-      geo: { lat: 10.4, lon: 44.5 }
+      geo: { lat: 10.4, lon: 44.5 },
     };
 
     const cfg2: EventConfig = {
@@ -78,3 +75,26 @@ Deno.test({
     console.log(calendar.toString());
   },
 });
+
+Deno.test('UTC event custom ID', () => {
+  const customId = '03bdde99-ede2-410e-b1b1-4c2a09d65b1f';
+  const cfg: EventConfig = {
+    customId,
+    title: 'test custom ID event',
+    beginDate: [2022, 8, 1, 10, 10],
+    endDate: [2022, 8, 1, 11, 10],
+    desc: 'Hello',
+    zone: 'utc', // Universal time required
+  };
+  const evt = new Event(cfg);
+  const lines = evt.toLines();
+
+  assertEquals(lines[0], ['BEGIN', 'VEVENT']);
+
+  assertEquals(lines[1][0], 'UID');
+  assertEquals(lines[1][1], customId);
+
+  assertEquals(lines[lines.length - 1], ['END', 'VEVENT']);
+
+  console.log(evt.toString());
+});
diff --git a/main.ts b/main.ts
index ccc4acb..e578bf8 100644
--- a/main.ts
+++ b/main.ts
@@ -17,18 +17,20 @@ const eventBegin: ContentLine = ['BEGIN', 'VEVENT'];
 
 const eventEnd: ContentLine = ['END', 'VEVENT'];
 
-const parseGeo = (geo?: {lat: number, lon: number}) => {
+const parseGeo = (geo?: { lat: number; lon: number }) => {
   return geo ? `${geo.lat};${geo.lon}` : undefined;
-}
+};
 
-const parseOrganizer = (organizer?: {name: string, email: string}) => {
-  return organizer? `CN=${organizer.name}:mailto:${organizer.email}` : undefined
-}
+const parseOrganizer = (organizer?: { name: string; email: string }) => {
+  return organizer
+    ? `CN=${organizer.name}:mailto:${organizer.email}`
+    : undefined;
+};
 
 export class Event {
-  zone: Zone = 'local'
-  constructor (protected config: EventConfig) {
-    if (config.zone) this.zone = config.zone
+  zone: Zone = 'local';
+  constructor(protected config: EventConfig) {
+    if (config.zone) this.zone = config.zone;
     if (config.duration !== undefined) {
       // Duration is provided
       if (!(config.beginDate instanceof Date)) {
@@ -48,13 +50,24 @@ export class Event {
   }
 
   toLines(): ContentLine[] {
-    const uid = crypto.randomUUID();
-    const { title, desc, rrule, alarm, location, url, organizer, geo, htmlContent } = this.config;
+    const {
+      customId,
+      title,
+      desc,
+      rrule,
+      alarm,
+      location,
+      url,
+      organizer,
+      geo,
+      htmlContent,
+    } = this.config;
+    const uid = customId ?? crypto.randomUUID();
 
     const result = [
       eventBegin,
       ['UID', uid],
-      ['DTSTAMP', parseDate(new Date(), "utc")],
+      ['DTSTAMP', parseDate(new Date(), 'utc')],
       ['DTSTART', parseDate(this.config.beginDate, this.zone)],
       ['DTEND', parseDate(this.config.endDate!, this.zone)],
       ['SUMMARY', title],
@@ -66,17 +79,21 @@ export class Event {
       ['ORGANIZER', parseOrganizer(organizer)],
       ...parseAlarm(alarm),
       eventEnd,
-    ].filter(line => line[1] !== undefined) as ContentLine[];
+    ].filter((line) => line[1] !== undefined) as ContentLine[];
 
     return result;
   }
+
+  toString() {
+    return stringifyLines(this.toLines());
+  }
 }
 
 export class Calendar {
   constructor(protected events: Event[]) {}
 
   toLines(): ContentLine[] {
-    const eventLines = this.events.map(evt => evt.toLines()).flat();
+    const eventLines = this.events.map((evt) => evt.toLines()).flat();
 
     return [calendarBegin, ...calendarProps, ...eventLines, calendarEnd];
   }
@@ -87,6 +104,7 @@ export class Calendar {
 }
 
 export interface EventConfig {
+  customId?: string;
   title: string;
   beginDate: DateData;
   endDate?: DateData;
@@ -96,10 +114,10 @@ export interface EventConfig {
   alarm?: AlarmConfig;
   location?: string;
   url?: string;
-  organizer?: { name: string; email: string; dir?: string; };
-  geo?: { lat: number; lon: number; };
+  organizer?: { name: string; email: string; dir?: string };
+  geo?: { lat: number; lon: number };
   htmlContent?: string;
-  zone?: Zone // default to local 
+  zone?: Zone; // default to local
 }
 
 export interface AlarmConfig {