Build a private mood tracker app that stays on your device

Designing the check-in

The check-in is the whole product. Keep the required part to one tap and make everything else optional:

Mood: a five-point scale, shown as words or simple shapes rather than emoji faces, so the scale reads the same on every device.
Tags (optional): a few things that might relate to mood, like sleep, exercise, work, social, alcohol, period, weather. Let the user edit the list.
Energy or anxiety (optional): a second scale for people tracking something specific.
A note (optional): one line, or more if they want.

Allow more than one entry a day for people whose mood changes, and allow editing yesterday's entry. Someone who missed a day should be able to fill it in without the app making a fuss.

Patterns worth showing

Calendar: A month grid coloured by mood. It's the screen people return to most, because a run of low days is obvious at a glance.
Trend: A line of the weekly average, smoothed, so single bad days don't dominate.
Tag comparison: Average mood on days with and without each tag: "days with exercise averaged 3.8, without 3.1". Note on screen that this shows association, not cause.
Time of day: If people log more than once, when highs and lows tend to fall.

These are descriptive, not diagnostic. The app shouldn't label anyone, predict anything or offer clinical advice.

Private by design, with a catch

Apps built with Anticode run in a sandbox with no network. A mood journal app built this way can't send entries anywhere, including to the site owner or to Anticode. Entries are saved in the browser on the device being used. Installed to a phone's home screen, it opens like any app and still keeps everything local.

The backup problem

Browser storage is not a safe place for a year of entries. Clearing site data, using a private window, a phone reset or simply switching browsers loses them, and there's no server copy to restore. Build backup in from day one:

Export to a file the user saves themselves, as JSON for re-importing and CSV for a spreadsheet.
Import that file on a new device or after clearing data.
A gentle reminder inside the app when the last export is more than a month old.
A clear note on the welcome screen explaining where the data lives.

Describing it

"A private daily mood log. Five-point scale shown as words and colours, editable tags, optional one-line note, multiple check-ins per day. Calendar view, weekly trend, and a tag comparison that says it shows association not cause. Everything stays on this device; export and import as JSON and CSV, with a reminder after 30 days without an export. Calm, soft design, large tap targets, dark mode. A short line at the bottom pointing to local support services, with a link I'll provide."

If you're building it for others, such as a counsellor's clients, each person gets their own empty tracker on their own device, and you never see their entries. Related builds: the habit tracker and journaling app.

What it can't do

No sharing with a therapist. Data doesn't leave the device, except as a file the user chooses to send.
No reminders when closed. It can't send notifications; use a phone alarm.
No crisis features. It can't detect risk or contact anyone. Include a visible link to appropriate support services, and don't present the app as a mental health service.
No sync. Phone and laptop each keep their own entries.

Questions people ask

Can a mood tracker app built this way be used without internet?

Yes. After the first visit it runs in the browser, and published sites can be installed with an offline fallback; test it offline before relying on it. Entries are local either way.

Can I see my clients' mood logs?

No. Each person's entries stay on their device. They could export a file and send it to you if they chose to.

Can it track medication or sleep hours?

Yes, ask for extra fields such as hours slept or a medication tick. They're stored alongside each entry and can appear in the comparisons.