Toast UI Calendar Alternative: Lightweight, Actively Maintained & Framework-Free

If you're searching for a Toast UI Calendar alternative, you've probably discovered something uncomfortable: the library you're evaluating hasn't shipped an update since August 2022. Toast UI Calendar has 12,700+ GitHub stars and a polished demo page — but stars don't fix bugs, and the 193 open issues in the repository tell a different story. Before you build on an abandoned foundation, it's worth understanding what Toast UI Calendar does well, where it falls short, and what the lighter alternatives look like.

What Toast UI Calendar offers

Toast UI Calendar (also known as TUI Calendar) is a JavaScript calendar component developed by NHN Cloud, a Korean tech company. Version 2.0 was a ground-up rewrite in TypeScript that introduced Preact as an internal rendering engine, Immer for state management, and DOMPurify for XSS protection. The result is a feature-rich library that supports daily, weekly, and monthly views, built-in drag-and-drop for creating and moving events, a default popup UI for adding and editing schedules, and milestone/task management alongside standard events.

The library ships framework wrappers for React (@toast-ui/react-calendar) and Vue (@toast-ui/vue-calendar), and it supports theming through a configuration object. For teams that adopted it in 2022 when v2.0 launched, it was a credible choice.

The problem is what happened — or rather, didn't happen — after that launch.

Where Toast UI Calendar creates friction

Abandoned maintenance

The last release on npm was v2.1.3 in August 2022. That's nearly four years without a patch, minor, or major update. The GitHub repository has 193 open issues and community questions in the Discussions tab go unanswered. A stale bot automatically closes valid bug reports after a period of inactivity — meaning bugs are silently swept under the rug rather than fixed.

Package health analyzers including Snyk classify tui.calendar's maintenance status as Inactive, and flag it as a potentially discontinued project. If you ship a production app on a library with no maintainer, every unpatched bug becomes your team's problem to solve.

Bundle weight: 81 KB gzipped

Toast UI Calendar v2.1.3 weighs 262 KB minified and ~81 KB gzipped. That's heavier than FullCalendar's base setup and nearly 6x heavier than a minimal calendar library. The weight comes from bundling Preact, Immer, and DOMPurify internally — dependencies you didn't ask for and can't tree-shake away.

If you use the React wrapper on top, you're shipping both React and a bundled copy of Preact — two virtual DOM implementations rendering the same calendar. That's not a trade-off; that's waste.

Google Analytics tracking by default

Toast UI Calendar sends your site's location.hostname to Google Analytics out of the box. The stated purpose is "to collect statistics on the use of open source." While you can disable it by setting usageStatistics: false, the opt-out design means your users' hostnames are shared with Google unless you know to flip that switch. For GDPR-conscious teams or privacy-focused products, this default is unacceptable.

No Vue 3 support

The @toast-ui/vue-calendar wrapper explicitly states: "Vue 3 is not supported." Only Vue 2 works. Since Vue 2 reached end of life on December 31, 2023, this leaves Vue developers with no viable path forward. The wrapper can't be updated because the core library isn't being maintained.

Framework wrappers add complexity

Toast UI Calendar's core is vanilla JavaScript with Preact internally, but the React and Vue wrappers add an adapter layer that introduces its own bugs. The old @toast-ui/react-calendar wrapper (before the monorepo migration) was documented as providing "no way to call instance methods of TOAST UI Calendar directly" — a significant limitation for programmatic control. DOM conflicts between React's reconciler and the library's internal Preact rendering have been reported in multiple issues.

Side-by-side comparison

Getting started with SimpleCalendarJS

Install and import:

npm install simple-calendar-js

import SimpleCalendarJs from 'simple-calendar-js';
import 'simple-calendar-js/dist/simple-calendar-js.min.css';

const calendar = new SimpleCalendarJs('#calendar', {
  defaultView: 'month',
  locale: 'en-US',

  fetchEvents: async (start, end) => {
    const res = await fetch(
      `/api/events?from=${start.toISOString()}&to=${end.toISOString()}`
    );
    return res.json();
  },

  onEventClick: (event) => console.log('Clicked:', event.title),
  onSlotClick: (date) => console.log('Slot:', date),
});

That's a complete calendar with async event loading, click handling, and locale support. One package, one import, zero configuration overhead. No Preact bundled inside, no Google Analytics phoning home, no adapter layer to debug.

Theming with CSS custom properties

Toast UI Calendar uses a JavaScript theme configuration object — you pass colours as strings in your init options. SimpleCalendarJS uses standard CSS custom properties, which means your styles live where styles belong:

.uc-calendar {
  --cal-primary: #4f46e5;
  --cal-primary-dark: #4338ca;
  --cal-today-bg: #eef2ff;
  --cal-font-size: 14px;
}

This works with CSS modules, Tailwind's @layer, SASS, or a plain <style> tag. Override a variable and every element referencing it updates — across all views, instantly.

Programmatic control

calendar.setView('week');   // 'month' | 'week' | 'day'
calendar.next();
calendar.previous();
calendar.today();
calendar.refresh();

The same imperative API works whether you're in a React useEffect, a Vue onMounted, a Svelte onMount, or a plain <script> tag. No framework-specific wrapper. No adapter that blocks access to instance methods.

When Toast UI Calendar might still fit

There are narrow scenarios where Toast UI Calendar's existing feature set justifies adopting an unmaintained library:

• Built-in popup UI: If you need a default creation/edit popup without building your own modal, TUI Calendar ships one. SimpleCalendarJS fires click events and leaves the UI to you.
• Milestone and task management: TUI Calendar treats milestones and tasks as first-class schedule types alongside events — a feature specific to project management interfaces.
• Drag-and-drop event creation: Drawing a time range on the weekly grid to create a new event is built in. Replicating this interaction from scratch requires effort.
• Existing integrations: If your application already runs on TUI Calendar and the current feature set is sufficient, migration has a real cost that should be weighed against the risk of running unmaintained code.

For any greenfield project, choosing a library that hasn't been updated in four years — and shows no signs of resuming development — is a risk that's hard to justify.

Summary

• Toast UI Calendar ships ~81 KB gzipped with Preact, Immer, and DOMPurify bundled inside. SimpleCalendarJS stays ~14 KB with zero dependencies — roughly 6x lighter.
• TUI Calendar's last npm release was August 2022. The repository has 193 open issues, unanswered discussions, and a stale bot closing valid bugs. Package health tools classify it as Inactive.
• The library sends your site's hostname to Google Analytics by default — a privacy concern that requires explicit opt-out.
• The Vue wrapper does not support Vue 3, and the React wrapper introduces DOM conflicts by layering React on top of the library's internal Preact rendering.
• TUI Calendar still makes sense for existing integrations that need its built-in popup UI, milestone management, or drag-and-drop creation — but for new projects, an actively maintained, lightweight alternative is the safer choice.

---

Sources & Further Reading

Research & References

• TOAST UI Calendar GitHub repository — nhn/tui.calendar
• TOAST UI Calendar documentation
• TOAST UI Calendar npm package — @toast-ui/calendar
• @toast-ui/calendar bundle size — Bundlephobia
• TOAST UI Calendar 2.0 release announcement — TOAST UI Blog
• TOAST UI Calendar Vue wrapper — Vue 3 not supported
• @toast-ui/calendar npm package health — Snyk Advisor
• Toast UI Calendar npm trends comparison

Image Credits

• Cover: Man writing code on a computer and laptop — Pexels

All images free to use under the Pexels License.