An offline-first freelancer app has one job: you can start a timer, log hours and produce an invoice with no connection, and nothing you recorded is lost. Sync, online payment and email are add-ons that sit on top of that core. They are not part of it. This guide lays out the design decisions in the order you’ll face them: storage, data model, timer, invoices, network boundaries, backup and testing. It uses current open-source and commercial apps as reference points. It describes patterns, not one private build, so none of the products below should be read as a description of any single app’s internals.
What “offline-first” should mean
Offline-first means the core workflow works with no network once the app is installed or loaded, and that local persistence is the primary path, not a cache of a server. It does not automatically include cross-device sync, card payments or email delivery. TaskTime Pro states this boundary plainly: its core works offline after the PWA is loaded or installed, and provider sync is optional (project README). Note the qualifier “after loaded or installed”: a web app still needs one online visit to fetch itself.
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Step 1: Pick a local storage engine
The platform decides the engine. Current examples fall into two camps.
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Desktop and mobile: SQLite
Upcount is a desktop app built with Tauri, SQLite, React and Ant Design; its README says business data stays local and includes backup and restore (Upcount). timedart uses Flutter with drift on SQLite and keeps data in the platform’s app-support directory (timedart). SQLite gives you relational integrity, which suits invoicing data where lines must point at real entries.
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Browser and PWA: IndexedDB
TaskTime Pro describes Yjs with IndexedDB, a choice that leaves room for conflict-free merging if sync is added later (TaskTime Pro). TimeDoco describes an offline PWA on IndexedDB (TimeDoco). The trade-off: browsers can evict site storage under pressure, so a PWA makes export more important, not less.
None of these is universally best. Choose by where your users already work, and by whether you ever expect multi-device use.
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Step 2: Model the work chain
The useful chain for a freelancer is client → project → task → time entry → invoice, which is how timedart structures its data (timedart). A few design rules follow from that chain. These are recommendations, not claims about any product:
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- Store rate and billable status on or alongside the entry or project, so an invoice line can trace back to the work.
- Mark entries as invoiced when an invoice is finalized, which prevents billing the same hour twice.
- Copy the rate and description onto the invoice line at finalization. Later rate changes then won’t rewrite history.
- Use stable unique IDs (such as UUIDs) rather than auto-increment integers if sync might ever arrive. Merging two devices’ integer IDs is painful.
Step 3: Make the timer survive anything
A timer should not count seconds in a running process. Laptops sleep, browsers kill tabs and phones suspend apps. The robust approach is to store the start timestamp and compute elapsed time as now minus start whenever you render. TimeDoco says it bases duration on absolute timestamps so the timer stays accurate through closing and restarting (TimeDoco). timedart describes one-key timer start (timedart).
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Edge cases worth deciding up front:
- Forgotten timers: offer to trim or split an entry that ran for an implausible length.
- Clock changes: store UTC timestamps and keep a display time zone separate, so travel or daylight saving doesn’t corrupt durations.
- Persist on start: write the running-timer record to disk immediately, not on stop. A crash then loses nothing.
- Manual edits: let users add and correct entries, since people forget to start timers.
Step 4: Turn selected work into an invoice
timedart’s flow is a good template: pick a project and date range, preview itemized entries and the total, then export a branded PDF (timedart). Generating that PDF is a local operation, so it needs no network.
Drafts versus final invoices
TaskTime Pro documents drafts that can be completed later, and its drafts do not reserve a final invoice number (TaskTime Pro). Assigning a number only at finalization avoids gaps and duplicates when people abandon drafts. If you later add multi-device sync, numbering needs a deliberate rule, because two offline devices can finalize at once.
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What to lock at finalization
- Invoice number and date
- Line descriptions, quantities and rates
- Client billing details as they were that day
- Tax settings, if you support them
Locking these makes the PDF reproducible and keeps it consistent with what you sent.
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| Action | Needs a connection? | Note |
|---|---|---|
| Start/stop timer, edit entries | No | Core local workflow |
| Create draft, finalize invoice, export PDF | No | Local rendering; timedart exports PDFs from local data |
| First load of a PWA | Yes, once | Offline afterward, per TaskTime Pro |
| Provider sync (Drive, Dropbox) | Yes | Optional in TaskTime Pro |
| Emailing an invoice, hosted payment page, reminders, reconciliation | Yes | Online service workflows |
Stripe documents hosted invoice links, PDF access and API automation for delivery and reconciliation (Stripe Invoicing). It also publishes claims that 87% of its invoices are paid within 24 hours and that customers pay three times faster on average with Apple Pay or Google Pay. Those are Stripe’s own figures from a regional page, with no methodology or year shown, so treat them as marketing, not an industry benchmark.
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A sensible design queues online actions: if the user taps “send” offline, mark the invoice as pending delivery and send when the connection returns. Billr takes a different route, advertising offline operation plus automatic sync and Stripe/PayPal connections (Billr). That suits users who want a connected account, at the cost of more moving parts.
Step 6: Give local data a recovery story
Local-first is not backup. If the only copy lives on one laptop or one browser profile, a dead disk or cleared site data ends the business record. The reference apps cover a range:
- TimeDoco advertises JSON export and restore (TimeDoco).
- Chronetic describes manual CSV/JSON export and optional Google Drive backup and sync that the user must switch on (Chronetic).
- TaskTime Pro offers optional Google Drive or Dropbox sync (TaskTime Pro).
- Upcount includes backup and restore for its local database (Upcount).
Whatever you choose, tell users plainly what stays on the device, what is uploaded, and what restoring requires. Test the restore path as seriously as the backup path. An export you’ve never re-imported is unproven. Prompting a periodic export, especially for browser storage, is cheap insurance.
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How the reference apps compare
| App | Platform | Local storage | Backup / sync | Invoices |
|---|---|---|---|---|
| Upcount | Cross-platform desktop | SQLite | Backup and restore | Invoicing and time tracking |
| timedart | Desktop, Android, browser demo (listed as beta) | SQLite via drift | Not stated | Itemized branded PDF |
| TaskTime Pro | Browser/PWA | Yjs + IndexedDB | Optional Drive/Dropbox sync | Drafts and PDFs |
| TimeDoco | PWA | IndexedDB | JSON export/restore | Not stated |
| Chronetic | iOS/macOS | Local database | Optional, user-activated backup/sync; CSV/JSON export | Not stated |
| Billr | Not stated | Not stated | Automatic sync | Stripe/PayPal payment connections |
These come from each project’s own pages and describe what the vendors claim, not independently tested behavior.
Quick Recap
Step 7: Test offline behavior deliberately
- Install or load the app, then disable the network (airplane mode, or browser DevTools offline). Run the full path from client creation through PDF export.
- Start a timer, force-quit the app or kill the tab, relaunch, and confirm elapsed time is correct.
- Put the machine to sleep with a timer running, wake it later, and check the duration.
- Finalize an invoice, change the project rate, and confirm the old invoice is unchanged.
- Abandon a draft and confirm the next finalized invoice number has no gap.
- Export, wipe app data, restore, and compare totals.
- Trigger an online action offline and confirm it queues or fails with a clear message, not silently.
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