Can AI build a focus timer app like Forest?

Build a personal focus timer web app to replace Forest for my own use. I understand this can't block other apps on my device.

Tech rules:
- Plain HTML, CSS, and vanilla JavaScript in one file, plus a small service-worker.js so it works offline. No framework, build step, account, or server.
- Store all data in localStorage under one key, with a version number.
- Use timestamps (start time plus elapsed real time via Date.now(), not a decrementing counter) so the timer stays accurate even if the tab is backgrounded or throttled.

Data model:
- Session: id, startedAt, plannedDurationSeconds, actualDurationSeconds, completed (boolean), type (focus or break), treeSpecies.
- Streak: currentStreakDays, longestStreakDays, lastSessionDate.

Features:
- Countdown timer with a selectable duration (not locked to 25 minutes), showing a tree that grows in stages as the session progresses.
- Stopwatch mode for open-ended sessions with no fixed end time.
- If I switch away from the tab or close it during an active focus session, mark the session as failed and show a "withered" tree state next time I open the app.
- Separate break timer mode with its own shorter default duration and a visually distinct color scheme so I can't confuse it with a focus session at a glance.
- Session history list showing date, duration, completed or failed, and tree type.
- Streak counter that increments only on days with at least one completed focus session, and resets if a day is missed.
- Screen Wake Lock API (where the browser supports it) to keep the screen on during an active session.

Edge cases the build must handle correctly:
1. Leaving the tab or switching apps mid-session kills the tree: use the Page Visibility API to detect when the tab loses focus during an active countdown, and mark the session failed if it happens before the planned duration elapses.
2. Track cumulative focus time and streaks across days, weeks, and months using calendar dates, not a rolling 24-hour window, so a session at 11pm and one at 1am the next day count as different days.
3. If a phone call, notification, or screen lock interrupts a session, use the Page Visibility API's hidden state to catch it the same way as switching apps, since a web page can't distinguish the interruption cause.
4. Custom session lengths are stored per session, not forced into a fixed 25-minute pomodoro block, and the tree's growth stages scale to whatever duration I picked.
5. Focus and break timer states are visually distinct (different colors, different tree behavior) and the app never lets me start a break session mid-focus-session without explicitly ending the focus session first.
6. Because JavaScript timers throttle or pause when a tab is backgrounded, calculate elapsed time from the stored startedAt timestamp compared to the current time, not from a decrementing interval counter, so the countdown stays accurate even after being backgrounded.
7. Session history persists across a browser refresh and reopening the app, since a lost tree isn't recoverable but the log of past sessions should never disappear.
8. If the browser tab is closed entirely mid-session without switching away first, treat the session as failed the next time the app opens and compare startedAt against the stored plannedDurationSeconds.

Backup:
- One-click "Export JSON" and "Export CSV" (one row per session).
- "Import JSON" restores after confirmation.

Layout:
- Mobile-first, readable at 375px wide, with the tree and timer as the dominant visual element.

Exclusions:
- No publishing, App Store submission, accounts, payments, real-money purchases, or cross-app/cross-site blocking. This tool cannot stop you from opening another app; it only tracks whether you did.

Write a short README explaining where data lives, how to export and restore it, and how to host it so it works offline after one online visit.

Keep it under 500 lines. This is a personal tool, not a product.

What is the short answer?

Yes, but. AI can build a tree-growing focus timer that replaces Forest Plus at $5.99 a month in 1–2 hours. It’s one of the simpler builds on this site.

The “but” is what Forest itself has become. Forest quietly retired the one-time-purchase Pro tier that made it a rare subscription-free favorite, and replaced it with a $5.99-a-month Plus plan plus real-money crystal purchases ($0.99 to $21.99) for tree species and coin boosts. That’s exactly the subscription-and-in-app-purchase model people switch to Forest to escape in the first place, which makes replacing it with a free personal build worth doing. The real limitation is technical, not financial: real cross-app distraction blocking needs OS-level permissions a web page can’t get.

Option	Best for	Upfront cost	Ongoing cost	Main limitation
Build a rough prototype	People who want the tree-growing visual and a basic timer	$0 and 1–2 hours	$0	No cross-app blocking, no streak tracking yet
Build a daily-use personal version	People who want streaks, custom durations, and accurate backgrounded timing	$0 and 4–6 hours	$0	Still can’t block other apps or sites during a session
Keep paying for Forest Plus	People who rely on Deep Focus to block distracting apps device-wide	$0	$5.99/mo or $32.49-$35.99/yr, plus optional crystal purchases	Subscription model replaced the one-time purchase people liked

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 the tree-growing feedback loop to feel motivating, and accurate timing that survives a backgrounded tab.

• Countdown timer with custom durations and a growing tree
• Tree fails visibly if you leave the tab mid-session
• Separate, visually distinct break timer mode
• Streak tracking across calendar days
• Session history log
• Deliberate exclusion: no cross-app or cross-site blocking, no in-app purchases.

What can AI build reliably?

ChatGPT and Claude build the timer and tree-growth visualization reliably. It’s a countdown with a visual state machine, a well-understood pattern.

Concrete things AI gets right:

• A tree that grows in stages as a session progresses and withers if you leave the tab
• Streak counting that resets correctly when a calendar day is missed
• Distinct visual states for focus vs break timers so they’re never confused
• Custom session lengths instead of a fixed pomodoro block

Where will AI need human help?

Background tab throttling is the trickiest technical edge case. Browsers slow down or pause JavaScript timers when a tab isn’t in focus, so a countdown built on a simple decrementing counter will drift and show an inaccurate time when you switch back. The starter prompt asks the AI to calculate elapsed time from a stored start timestamp instead, but test this yourself: start a session, switch away for a few minutes, and check the timer catches up correctly when you return.

Distinguishing an interruption (a phone call, a notification, a screen lock) from you deliberately leaving is not something a web page can do. The Page Visibility API only reports whether the tab is hidden, not why. Decide for yourself whether you’re okay with any tab-switch killing the tree, even an accidental one, since that’s the only signal available.

The decision only you can make: real distraction blocking needs OS-level screen-time permissions (iOS Screen Time API, Android Digital Wellbeing) or a native app; at most a browser extension can block other browser tabs. A plain web page cannot enforce this at all. If Forest’s Deep Focus mode blocking other apps device-wide is the feature you actually use, a DIY web timer doesn’t replace it.

Privacy is low-stakes here. It’s a focus timer with no account, staying local to your device.

Can I get my data out of Forest?

Uncertain. A reported path is the hamburger menu, then Settings, Your Profile, and “Export your Data,” which downloads a CSV of session history, apparently without needing a paid plan. This comes from a third-party open-source tool’s README, not from Forest’s own documentation [VERIFY], since Forest’s help center was unreachable during research.

It’s also unclear whether the exported CSV includes abandoned or killed sessions, coin and currency history, tags, or real-tree-planting records, or only successfully completed focus sessions [VERIFY]. Treat any export as likely incomplete until you confirm it directly in the app.

The practical path: if you want your streak history to carry over, manually note your current streak length and rough session count before switching, since there’s no confirmed structured export of that data to import automatically.

How long will it take and what will it cost?

Rough prototype: 1–2 hours and $0. Timer, tree animation, and check-off completion.

Dependable daily-use version: 4–6 hours, including streak tracking, accurate backgrounded timing, and session history. Build it on a free AI plan.

Forest Plus costs $5.99 a month, or roughly $32.49 to $35.99 a year depending on region and platform. A $20 month of a paid AI plan equals over 3 months of Forest Plus. Build only on a free plan, or build because you specifically want to avoid the crystal-purchase model, not to save a large amount of money.

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

Which AI tool or approach should I use?

Claude or ChatGPT on a free plan is enough. This build fits comfortably in one conversation.

Cursor is unnecessary here. The timer logic is small.

Lovable doesn’t add much value for this build, since there’s no need for a hosted database or accounts for a single-device timer.

What will I need to maintain?

Very little. Two files on a free static host.

Recurring work:

• Export a JSON backup occasionally so your streak history isn’t only on one device
• Open the app online occasionally so the cached offline version stays current
• Re-check the timer’s accuracy after a browser update, since background-tab throttling behavior can change

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

Build it if you want the tree-growing motivation without a subscription or crystal purchases, and you don’t rely on cross-app blocking to stay focused.

Buy it if Forest’s Deep Focus mode blocking other apps device-wide is the feature that actually keeps you off your phone. No personal web app can replicate that enforcement.

Reduce scope if you just want a plain countdown timer with no visual theme. Your phone’s built-in timer or clock app already does that for free.

Recommendation: build your own if the tree visualization is what motivates you and you can rely on willpower rather than enforced blocking. Keep Forest Plus if Deep Focus’s actual app-blocking is doing real work for your focus, since that’s a technical capability a web page can’t match. If you’re tracking the time itself rather than the visual streak, see the Toggl Track build, or pair this with a habit tracker for the daily streak habit.

What if I wanted to ship this to other people?

Shipping a focus timer to other people means competing in a crowded, mostly-free app category, and any real distraction-blocking feature would require a native app with OS-level permissions, not a web page. That’s a much larger project than a personal timer you host for yourself.

Starter build specification

• User: You, for your own use, wanting a visual focus timer without a subscription.
• Problem: Paying $5.99 a month or buying crystals for a feature that’s really just a timer with a growing tree animation.
• Core workflow: Pick a duration, start the session, watch the tree grow, don’t switch tabs.
• Required features: Countdown and stopwatch modes, tree growth and withering, streaks, session history, custom durations.
• Deliberate exclusions: No cross-app blocking, no in-app currency purchases, no accounts.
• Data ownership: Stored in localStorage. Exported as JSON and CSV. Imported from JSON.
• Definition of done: Starting a 10-minute session, switching to another tab for 2 minutes, and returning shows the correct remaining time and marks the tree as withered.

For scoping help, read can AI build an app for me.

Sources and verification

• Forest on the App Store: current pricing for Forest Plus and crystal purchases, discontinued one-time Pro purchase.
• Forest official site: free tier feature list and Deep Focus mode description.
• track-focus README (pkg.go.dev): third-party description of Forest’s data export path, not officially confirmed.

This app was not built and tested for this page. The verdict is based on Forest’s App Store listing and official site; Forest’s own help center was unreachable during research. Forest’s price was checked on September 24, 2026.

Reviewed on September 24, 2026.