Can AI build a to-do list app like Todoist?

Build a personal to-do list web app to replace Todoist for my own use.

Tech rules:
- Plain HTML, CSS, and vanilla JavaScript in one file. No framework, build step, account, or server.
- Store all data in localStorage under one key, with a version number in the saved object.

Data model:
- Task: id, title, notes, projectId, parentId (one level of subtasks), priority (1 highest to 4 none), dueDate (YYYY-MM-DD local), recurrence (none | daily | weekdays | weekly | monthly), completedAt, createdAt.
- Project: id, name, color, order.

Features:
- Quick-add bar that accepts "today", "tomorrow", and weekday names (mon–sun) at the end of the title as the due date.
- Views: Today (overdue first, then today), Upcoming (next 7 days), each Project, and Completed (last 30 days).
- Check off with a 5-second undo.
- Edit, delete, reorder, and move tasks between projects.

Edge cases the build must handle correctly:
1. Calculate "today" from the device's local date, never from toISOString(), so tasks don't shift a day near midnight.
2. Completing a recurring task moves its dueDate to the next occurrence. It never creates a duplicate task.
3. Monthly recurrence on the 29th, 30th, or 31st falls back to the last day of shorter months.
4. "Weekdays" recurrence skips Saturday and Sunday.
5. Deleting a project asks what to do with its tasks (delete or move to Inbox).
6. Deleting a parent task also deletes its subtasks after one confirmation.
7. Empty or whitespace-only titles are rejected.
8. If localStorage is full or unavailable, show a clear error instead of silently losing the task.

Backup and import:
- One-click "Export JSON" and "Export CSV" buttons.
- "Import JSON" restores a full backup after a confirmation that it replaces current data.
- "Import Todoist CSV" reads Todoist's project export (TYPE, CONTENT, DESCRIPTION, PRIORITY, INDENT, DATE columns), imports rows where TYPE is "task", and treats INDENT 2 as a subtask. Show how many tasks imported and how many were skipped.

Layout:
- Mobile-first, thumb-friendly, readable at 375px wide. Works in Safari and Chrome.

Exclusions:
- No publishing, App Store submission, accounts, login, payments, sharing, collaboration, or social features.

Also write a short README that explains where the data lives, how to export and restore it, and that clearing browser data deletes everything.

Keep it under 900 lines. This is a personal tool, not a product.

What is the short answer?

Yes. AI can build a to-do list app that replaces Todoist Pro at $7 per month or $60 per year for one person in a single afternoon. It’s worth it if you use Todoist on one device and mostly need a Today list, projects, and repeating tasks.

The trade-off is sync and reminders. A local web app keeps your tasks in one browser and won’t notify you when the tab is closed. If you check your list on a phone and a laptop every day, that gap matters more than the $7.

Option	Best for	Upfront cost	Ongoing cost	Main limitation
Build a rough prototype	People who want to test whether a Today list and projects cover their Todoist use	$0 and 2–3 hours	$0	Recurring tasks and date edge cases are untested
Build a daily-use personal version	People who manage personal tasks on one main device and want no monthly fee	$0–$20 and 6–10 hours	$0	No cross-device sync or closed-app reminders
Keep paying for Todoist Pro	People who need reminders, sync across phone and laptop, or shared projects	$0	$7/mo or $60/yr	Monthly cost for features you might not use

The ready-to-paste starter prompt at the end of this page builds the daily-use version.

What should the first version include?

The first version needs a fast way to add a task and a Today view you trust. Everything else comes after a week of use.

• Quick-add with a due date typed in plain words (“tomorrow”, “fri”)
• Today view with overdue tasks pinned on top
• Projects and one level of subtasks
• Simple recurring tasks: daily, weekdays, weekly, monthly
• JSON backup, restore, and a Todoist CSV importer
• Deliberate exclusion: no reminders, no sync, no sharing. These need a server, and they’re the reason the build stays small.

If you plan your day in time blocks rather than lists, a daily planner like Structured is the closer fit.

What can AI build reliably?

ChatGPT and Claude produce a working single-file to-do app on the first try. The list, checkboxes, projects, and localStorage saving work out of the box because thousands of similar examples exist.

Concrete things AI gets right quickly:

• A quick-add bar that parses “today”, “tomorrow”, and weekday names
• Filtered views for Today, Upcoming, and each project
• Drag-to-reorder and move-to-project
• Export buttons that download JSON and CSV
• A 5-second undo toast after check-off

Priority colors, dark mode, and keyboard shortcuts are also quick wins once the core works.

Where will AI need human help?

AI needs your help with dates. The most common bug in AI-built to-do apps is using UTC dates, which makes tasks jump to tomorrow in the evening or show as overdue in the morning, depending on your timezone. Test your Today view at 11 p.m. and just after midnight.

Recurring tasks are the second trap. When you tick off “water plants, every weekday”, the task must move to the next weekday. AI often creates a new copy instead, and your list fills with duplicates. Test completing a recurring task 3 days in a row.

Other checks to run yourself:

• A monthly task on the 31st in a 30-day month
• Deleting a project that still holds tasks
• Importing a Todoist CSV with subtasks

Privacy is simple for personal use. Your tasks never leave your browser. The flip side is that clearing browser data deletes everything, so the backup button is not optional.

Can I get my data out of Todoist?

Yes. Todoist lets any plan export a project as a CSV file from the project’s three-dot menu. The file includes tasks, sections, descriptions, dates, and comments.

The trap: completed tasks are left out. Breeze’s walkthrough of Todoist exports notes this is by design, and that archived projects can’t be exported at all. If your completed history matters, unarchive old projects and copy what you need before you cancel.

Export is one project at a time. With 12 projects, you’ll download 12 files. Paid plans also keep automatic backups, but those don’t include completed tasks either.

To import into your build, use the starter prompt’s “Import Todoist CSV” button. It reads rows where TYPE is “task” and treats INDENT 2 as a subtask. Check how priorities come through after import, because Todoist’s CSV numbering may run opposite to the in-app labels [VERIFY].

How long will it take and what will it cost?

Rough prototype: 2–3 hours and $0 on a free ChatGPT or Claude plan. You’ll have a working list, projects, and Today view.

Dependable daily-use version: 6–10 hours across a week, including fixes for date bugs and recurring tasks. $0–$20 if you pay for one month of an AI plan to speed up the fixes.

Against Todoist Pro at $7 per month, a $20 AI month pays for itself in about 3 months. On the annual plan ($60 per year), it takes about 4 months. If you build on a free plan, the only cost is your time.

These figures are estimates from reviewing the feature set. They are not measurements from a completed test build.

Which AI tool or approach should I use?

Claude is a good default. It previews single-file HTML apps directly in the chat, so you can click through the Today view before saving anything.

ChatGPT works equally well for the first version. Paste the starter prompt, save the output as index.html, and open it in your browser.

Cursor is the better choice once the file passes 500 lines and you want to fix one bug without regenerating the whole app.

Lovable builds faster-looking results but pushes you toward accounts and a hosted database, which adds the maintenance you’re trying to avoid.

What will I need to maintain?

Almost nothing. The app is one HTML file with no server, no API, and no bill.

Your recurring work:

• Export a JSON backup once a week and save it somewhere outside the browser
• Re-open the app in the same browser; a different browser or a private window starts empty
• Fix small bugs as you find them during the first 2 weeks

If you want the app on your phone, save the file to your phone’s Files app or put it on a free static host and add it to your home screen. Hosting publicly means anyone with the link can open the empty app, but your tasks stay in your own browser.

Should I build it, buy it, or reduce scope?

Build it if you use Todoist on one device, rely on Today and a handful of projects, and don’t need notifications.

Buy it if you need reminders that fire when your phone is locked, tasks synced between phone and laptop, or shared projects with a partner. Todoist handles all three well, and rebuilding sync yourself is a much bigger project.

Reduce scope if you mostly use Todoist as a daily checklist. Build only a Today list with recurring items, or use the habit tracker build for repeat routines.

Recommendation: build it if you’re on a single device and cancel Pro after 2 weeks of parallel use. Keep Todoist if phone reminders are how you remember things, because a web page can’t replace that reliably.

What if I wanted to ship this to other people?

Shipping this means adding accounts, a database, cross-device sync with conflict handling, and push notifications. That’s a separate project measured in weeks, not hours. The personal build above is a starting point, not a shortcut to a product.

Starter build specification

• User: You, for your own use.
• Problem: Paying $7 per month for Todoist Pro when you use a Today list, a few projects, and repeating tasks on one device.
• Core workflow: Open app, add a task with a date, check it off today, see tomorrow’s list.
• Required features: Quick-add with dates, Today and Upcoming views, projects, one level of subtasks, simple recurrence, undo.
• Deliberate exclusions: No accounts, no sync, no reminders, no sharing, no store submission.
• Data ownership: Stored in your browser’s localStorage. Exported as JSON and CSV. Imported from JSON backups and Todoist project CSVs.
• Definition of done: You import one Todoist project, complete a weekday-recurring task on Friday, and it reappears on Monday, not Saturday, with no duplicate. The Today view is correct at 11:55 p.m. and 12:05 a.m.

For more on scoping a first build, read can AI build an app for me. If you bill clients for your time, pair this with a personal time tracker.

Sources and verification

• Todoist Pro pricing update (Todoist Help Center): Pro price of $7 per month or $60 per year from December 10, 2025.
• Import or export a project as a CSV file (Todoist Help Center): CSV export steps and contents.
• Todoist CSV export, backups, and completed tasks (Breeze): completed tasks excluded from CSV, archived projects not exportable.
• How much does Todoist cost (Hack’celeration): free plan 5-project cap [VERIFY on Todoist’s pricing page].

This app was not built and tested for this page. The verdict is based on a review of Todoist’s documentation and the feature set. Todoist’s price was checked on September 24, 2026.

Reviewed on September 24, 2026.