Can AI build a mood tracker app like Daylio?

Build a personal mood tracker web app to replace Daylio Premium 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.

Data model:
- Entry: id, date (YYYY-MM-DD local), time (HH:MM), mood (1–5), activities [activityId], note, createdAt.
- Activity: id, name, icon (emoji chosen by me), group (for example Social, Health, Work), archived.
- Mood labels: editable names for levels 1–5 (default: awful, bad, meh, good, great).

Features:
- Home screen: 5 large mood buttons. One tap logs the mood for now, then shows activity chips and an optional note.
- Edit or delete any past entry. Add an entry for a past date.
- Calendar view with each day colored by average mood.
- Year in Pixels: a 12 x 31 grid for the selected year.
- Monthly line chart of daily average mood.
- Stats: average mood with and without each activity, average mood by weekday, longest logging streak.

Edge cases the build must handle correctly:
1. Multiple entries on one day: the day's color uses the average. Show each entry in the day view.
2. Stats only show an activity after it has at least 5 entries. Otherwise display "not enough data yet".
3. Use the device's local date, never toISOString(), so late-night entries land on the right day.
4. Archiving an activity hides it from logging but keeps it in past entries and stats.
5. Renaming an activity updates it everywhere, because entries store activity ids, not names.
6. Days with no entry show as empty in Year in Pixels, never as the lowest mood.
7. Charts render correctly with 1 entry and with 2,000 entries.

Reminders:
- "Export reminder (.ics)" creates a daily recurring calendar event at a time I choose, so my phone calendar reminds me to log.

Privacy:
- Optional 4-digit PIN screen. Make clear in the settings text that this hides the screen but doesn't encrypt the data.

Backup and import:
- One-click "Export JSON" and "Export CSV" (one row per entry, activities joined with a pipe character).
- "Import JSON" restores a backup after confirmation.
- "Import Daylio CSV": map date, time, mood, activities, and note columns. Let me map Daylio's mood names to my 1–5 scale. Report imported and skipped rows.

Layout:
- Mobile-first, one-thumb logging at 375px wide, dark mode.

Exclusions:
- No publishing, App Store submission, accounts, cloud sync, payments, AI analysis, or social features.

Write a short README explaining where data is stored, how to export and restore it, and that clearing browser data deletes all entries.

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

What is the short answer?

Yes. AI can build a mood tracker that replaces Daylio Premium at $4.99 per month or $35.99 per year for your own use. A private tracker with one-tap logging, activity tags, and charts takes 2–3 hours to build.

The twist: Daylio’s free tier already handles logging. What Premium sells is mostly the advanced stats, like mood by activity and by weekday. That math is simple averages, which makes it the easiest part of the whole build. The harder part is reminders, since a web page can’t nudge you at 9 p.m. when it’s closed.

Option	Best for	Upfront cost	Ongoing cost	Main limitation
Build a rough prototype	People who want to log daily mood and see a monthly chart	$0 and 2–3 hours	$0	Stats and multi-entry days untested
Build a daily-use personal version	People who want Daylio’s advanced stats and full data ownership without a subscription	$0–$20 and 6–8 hours	$0	Reminders run through your calendar, not the app
Keep paying for Daylio Premium	People who want polished native reminders, widgets, and automatic cloud backups	$0	$4.99/mo or $35.99/yr	Stats you view on your own data sit behind a paywall

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 must log a mood in under 5 seconds. If logging takes longer, you’ll stop after a week, and the stats never get enough data.

• One-tap mood on a 5-point scale
• Activity tags and an optional note
• Editing past days and multiple entries per day
• Year in Pixels and a monthly mood chart
• Mood by activity and by weekday
• JSON and CSV export
• Deliberate exclusion: no cloud sync and no AI insights. Your mood data never leaves your device.

What can AI build reliably?

ChatGPT and Claude build mood trackers well because the data is small and structured: a date, a number, a few tags. Charts and grids come out right on the first or second try.

Concrete things AI gets right:

• Large mood buttons and emoji activity chips
• A Year in Pixels grid colored by average mood
• A monthly line chart without any chart library
• “Average mood with this activity vs. without” comparisons
• A calendar .ics file with a daily repeating reminder

A developer who hit Daylio’s stats paywall built and published an open-source alternative for exactly this reason. A personal version is much smaller than that.

Where will AI need human help?

The stats need your judgment. With 3 entries tagged “gym”, the app might claim gym days are 40% happier. That’s noise, not insight. The starter prompt hides stats until an activity has 5 entries. Raise that to 10 if you want more caution.

Other checks:

• Log at 11:50 p.m. and confirm it lands on today, not tomorrow
• Log twice on one day and confirm the pixel shows the average
• Leave a day empty and confirm it stays blank instead of showing as your worst mood

Privacy is the main reason to build this. Mood data is personal. In a local web app, it stays in your browser with no server. The PIN screen is a curtain, not a lock: anyone with your unlocked phone and some technical knowledge can read browser storage. Say so in your own settings text, as the prompt requires.

A mood tracker is a journal, not a clinical tool. If your chart shows a long low stretch, that’s worth talking about with someone you trust or a professional.

Can I get my data out of Daylio?

Mostly yes. Daylio can export your logged entries as a CSV file, and Premium adds automatic backups and PDF export, according to a developer’s breakdown of the free and paid tiers. Some reviews suggest export is effectively a Premium reason, so check your version before cancelling [VERIFY].

The trap: Daylio’s own backup file is built for restoring into Daylio, not for other apps [VERIFY format]. Use the CSV export for moving data, not the backup.

After export, the starter prompt’s importer asks you to map Daylio’s mood names to your 1–5 scale. If you renamed moods in Daylio, map them carefully, or your history shifts by one level. Spot-check 5 random days against Daylio before cancelling.

How long will it take and what will it cost?

Rough prototype: 2–3 hours and $0. Logging, calendar, and a monthly chart.

Dependable daily-use version: 6–8 hours across a week, including stats, the Daylio importer, and edge-case fixes. $0–$20 for one optional AI month.

Daylio Premium costs $35.99 per year. A $20 AI month equals about 7 months of the annual plan. On monthly billing at $4.99, you break even in about 4 months.

These are estimates from reviewing the feature set, not measurements from a completed build.

Which AI tool or approach should I use?

Claude previews the tracker in the chat, which is useful for tuning colors and button sizes before you commit.

ChatGPT is equally capable and good at explaining what each stat means, so you don’t overread your chart.

Cursor is worth it if you keep extending the stats over months.

Lovable adds accounts and cloud storage by default. For mood data, that’s the opposite of what you want.

What will I need to maintain?

Nothing beyond backups. No server, API, or bill.

Recurring work:

• Export a JSON backup monthly, and store it somewhere private
• Keep using the same browser on the same phone
• Re-import the .ics reminder if you change the time

If you host the file online so your phone can add it to the home screen, the page is public but your entries aren’t. They live only in your browser.

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

Build it if you log mood daily, want Daylio’s advanced stats, and prefer data that never touches a server.

Buy it if native reminders and home-screen widgets are what keep you logging. A missed reminder costs more than $35.99 if it breaks the habit.

Reduce scope if you already track habits. Add a 1–5 mood field to the habit tracker build instead of building a second app.

Recommendation: build it. Daylio charges for stats on your own data, and those stats are a few lines of arithmetic. Keep Daylio only if you tried calendar reminders for 2 weeks and still forgot to log. For longer reflections, pair it with the Day One-style journal build, and see the Sleep Cycle build if you want to compare mood with sleep. The Flo build uses the same local-only privacy approach.

What if I wanted to ship this to other people?

Shipping a mood tracker means handling sensitive health-adjacent data for others: accounts, encryption, privacy policies, and store review for wellness apps. That’s a far bigger responsibility than a tracker on your own phone.

Starter build specification

• User: You, for your own use.
• Problem: Paying $35.99 per year for Daylio Premium mainly to see stats on your own mood data.
• Core workflow: Tap a mood, tag activities, close the app. Once a week, check which activities line up with better days.
• Required features: One-tap logging, activities, notes, past-day editing, Year in Pixels, monthly chart, mood by activity and weekday, .ics reminder.
• Deliberate exclusions: No accounts, no cloud sync, no AI analysis, no store submission.
• Data ownership: Stored in localStorage. Exported as JSON and CSV. Imported from Daylio’s CSV export.
• Definition of done: You import your Daylio history, log 2 entries today, and the day shows their average. An activity with 3 entries shows “not enough data yet” instead of a percentage.

Sources and verification

• Daylio on the App Store (US): Premium at $4.99 and $35.99 [VERIFY which is monthly and which is annual in-app].
• I built a free, open-source Daylio alternative (DEV Community): Premium pricing, 7-day trial, and features locked on the free tier.
• Daylio (Wikipedia): CSV export of logged statistics.

This app was not built and tested for this page. The verdict is based on Daylio’s store listing, third-party reviews, and a review of the feature set. Daylio’s price was checked on September 24, 2026.

Reviewed on September 24, 2026.