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Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →In a local-first app, your device holds the primary copy of your data; servers or other devices may hold secondary copies. A save can be recorded locally before it syncs. When devices make overlapping edits, the app’s conflict policy—not the word “save” or “sync”—decides which value survives or whether someone must choose.
What does “save” mean in a local-first app?
“Saved” can describe separate events: an edit is persisted on your device, then later synchronized to other devices or a service. Those events need not happen together. An app may accept and store an offline edit even though no other device has received it yet.
That distinction follows from the local-first idea of which copy is primary. Martin Kleppmann, Adam Wiggins, Peter van Hardenberg, and Mark McGranaghan write in their 2019 paper Local-First Software: You Own Your Data, in spite of the Cloud: “In local-first applications we swap these roles: we treat the copy of the data on your local device — your laptop, tablet, or phone — as the primary copy.” They add that servers can still exist as secondary copies that help people access their data from multiple devices.
This is an architectural choice about authority, not a promise that a server disappears or that devices must communicate peer to peer. In a cloud-centered design, a server may be authoritative and the device may hold a cache. In a local-first design, the device copy is primary, while synchronization lets other replicas catch up.
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- Persistence means writing an edit to storage the app relies on, such as local storage.
- Synchronization means exchanging changes among replicas when communication is available.
- Conflict resolution means deciding how to combine edits made before the devices had seen one another’s changes.
These are related but distinct responsibilities. An app’s save indicator should make clear whether it acknowledges local persistence, remote confirmation, or both.
What happens when you edit offline?
A local-first app can let you continue working while disconnected: it records changes on the device, then sends or receives changes when a connection becomes available. Automerge’s official introduction describes making local edits offline and syncing later. Yjs describes synchronization when changes can be exchanged in its documentation.
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That behavior does not, by itself, prove that a particular app has configured local storage correctly, that queued updates will be delivered, or that a save has reached another device. The app still needs to define where local data is persisted, how it retries pending updates, and what happens if syncing fails.
When do concurrent edits merge cleanly?
CRDT-based systems are designed so replicas that receive the same changes can converge without a central server serializing every edit. This is useful when edits are independent: for example, two devices can add different tasks to a list or change different objects.
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The hard case is semantic overlap. If two devices change the same property of the same object while disconnected—such as assigning different due dates to one task—the system needs a rule. It might select a deterministic winner, retain competing values, apply domain-specific logic, or ask the user. The local-first paper explains that concurrent changes to one property can leave the application or user to resolve the competing values; Automerge’s repository documentation describes selecting a winner for concurrently written values.
“Conflict-free” therefore does not mean “the software knows which value the user intended.” A deterministic result can make replicas agree while still being the wrong result for a particular task. The right rule depends on what the data represents. A list, text sequence, counter, or financial record may each need different behavior; domain-specific rules and invariants remain the app’s responsibility.
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How do Automerge, Yjs, and custom sync differ?
This is a way to frame an evaluation, not a performance benchmark or a recommendation for every project. Library capabilities and compatibility can change, so check the project documentation for the platforms, data types, persistence integrations, and providers you need.
| Decision axis | Automerge | Yjs | Application-specific sync |
|---|---|---|---|
| Core model | CRDT library; project material describes automatic concurrent merging, change history, and branching workflows. Automerge repository | CRDT library with shared types and automatic synchronization; documentation emphasizes editor integrations and modular network providers. Yjs docs · Yjs homepage | Can encode domain rules directly; the team owns correctness and reconciliation behavior. |
| Offline work | Official introduction describes local edits while offline and later synchronization. Automerge introduction | Homepage describes offline support with local persistence integrations such as IndexedDB. Yjs homepage | Depends on the app’s local persistence and queued-operation design. |
| Conflict boundary | Concurrent writes to one property can leave multiple values; repository documentation describes selecting a winner. Automerge repository | Shared types merge automatically; the selected type and application semantics determine how overlapping edits behave. Yjs docs | Rules can be specified per field, including rejecting an update or asking a user when no automatic answer is appropriate. |
| Networking | Network-agnostic data structure; project material also allows centralized servers. Automerge repository | Network-agnostic and decoupled from the provider; docs name hosted provider options for teams that do not want to maintain a backend. Yjs docs | The team chooses or builds the transport and server protocol. |
| Useful evaluation question | Do you need structured local-first state, history, or branching and merging workflows? | Do you need collaborative shared types and a particular editor or provider ecosystem? | Are your conflict rules important and manageable enough to implement explicitly? |
Yjs separates its data model from its networking layer, while Automerge documents change-oriented history workflows. Neither library choice removes the need to plan local persistence, data migration, delivery, and recovery.
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What should an app tell you about saves and conflicts?
Before relying on a local-first app for important work, look for clear answers to these questions:
- What is stored on this device, and what can be reconstructed from a remote service?
- Does “saved” mean the edit reached local storage, a remote service, or both?
- What happens to offline edits, and how are queued changes retried?
- When two devices change the same field, does the app choose a value, preserve alternatives, apply a domain rule, or ask you?
- Can you inspect history or recover an earlier value if an automatic choice loses important intent?
- How does the app handle data-format changes when an older and newer version access the same data? The local-first paper identifies evolving formats as a challenge, but there is no universal migration solution.
Does synchronization count as a backup?
No. Replication helps devices share changes; it does not automatically provide an independent recovery copy. Depending on an app’s design, an accidental deletion or corrupted change could be synchronized too. Ask whether you can export your data and how to restore it after device, account, or data loss. The local-first sources establish long-term access as a goal, but do not prescribe a backup schedule or medium.
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