ElectricSQL vs PowerSync vs Zero: Best Local-First Sync Engine (2026)

Local-first is the hottest architecture trend in 2026. Apps that work offline, sync instantly, and feel native — without the complexity of building your own sync engine.

ElectricSQL, PowerSync, and Zero (by Rocicorp) represent three approaches to the same problem: keeping local data in sync with a server. Here's how they compare.

What Is Local-First?

Local-first apps store data on the client (browser, mobile device) and sync changes to/from a server. Benefits:

• Instant UI — reads are local, no network latency
• Works offline — full functionality without internet
• Real-time collaboration — changes sync across devices
• Resilient — network issues don't break the app

The hard part: conflict resolution when multiple clients modify the same data offline.

Quick Comparison

Feature	ElectricSQL	PowerSync	Zero
Approach	Postgres sync to client	Postgres sync to client	Client-side reactive cache
Server database	PostgreSQL	PostgreSQL	Any (via server API)
Client storage	SQLite (PGlite)	SQLite	IndexedDB
Conflict resolution	Last-write-wins (LWW)	Custom (you define)	Server-authoritative
Sync protocol	Electric (HTTP streaming)	PowerSync protocol	Zero protocol
Offline support	Yes	Yes	Yes
Partial sync	Shape-based subscriptions	Sync rules	Queries define sync
Framework support	React, React Native	React, React Native, Flutter	React
Open source	Yes (Apache 2.0)	Partially (client SDK)	Yes
Self-host	Yes	Yes (cloud or self-host)	Yes

ElectricSQL: Postgres Shapes to the Client

ElectricSQL syncs PostgreSQL data to client-side SQLite using "shapes" — declarative subscriptions that define what data the client needs.

How It Works

1. Define a "shape" (subset of Postgres data)
2. ElectricSQL streams that shape to the client
3. Client gets a local SQLite copy
4. Changes sync bidirectionally
5. Conflicts resolved via last-write-wins

import { useShape } from '@electric-sql/react';

function TodoList({ projectId }) {
  const { data: todos } = useShape({
    url: `${ELECTRIC_URL}/v1/shape`,
    params: {
      table: 'todos',
      where: `project_id = '${projectId}'`,
    },
  });

  return todos.map(todo => <TodoItem key={todo.id} todo={todo} />);
}

Strengths

• PostgreSQL-native. Your server database is standard Postgres. No special schema or setup.
• Shape subscriptions. Clients only sync the data they need. Efficient for large datasets.
• PGlite option. Run Postgres itself in the browser via WASM. Full SQL locally.
• Open source. Apache 2.0 license. Self-host the sync service.
• Active-active writes. Write to Postgres directly OR through Electric. Both paths sync.

Weaknesses

• Last-write-wins only. Conflict resolution isn't customizable (yet). Fine for most apps, limiting for collaborative editing.
• Early stage. Still evolving rapidly. Breaking changes between versions.
• React-focused. Best support is React/React Native. Other frameworks have less mature integrations.
• Sync latency. Not as instant as Zero's optimistic approach for UI updates.

Best For

Apps that want to add local-first to an existing PostgreSQL backend with minimal changes. Shape-based sync is intuitive and powerful.

PowerSync: Production-Ready Postgres Sync

PowerSync is the most production-tested local-first sync engine. It syncs PostgreSQL to client-side SQLite with flexible sync rules and conflict handling.

How It Works

1. Define sync rules (which data goes to which users)
2. PowerSync streams changes to client SQLite
3. Client reads/writes to local SQLite
4. Writes upload to server via your API
5. You control conflict resolution in your API

import { usePowerSync, useQuery } from '@powersync/react';

function TodoList({ projectId }) {
  const { data: todos } = useQuery(
    'SELECT * FROM todos WHERE project_id = ? ORDER BY created_at',
    [projectId]
  );

  const powerSync = usePowerSync();
  
  const addTodo = async (title: string) => {
    await powerSync.execute(
      'INSERT INTO todos (id, title, project_id) VALUES (uuid(), ?, ?)',
      [title, projectId]
    );
    // Automatically syncs to server
  };

  return todos.map(todo => <TodoItem key={todo.id} todo={todo} />);
}

Strengths

• Production-tested. Used in production apps with millions of users. The most battle-tested option.
• Custom conflict resolution. You handle writes through your own API, giving full control over conflict resolution logic.
• Sync rules. Fine-grained control over which data syncs to which users. Essential for multi-tenant apps.
• Multi-platform. React, React Native, Flutter, Kotlin, Swift. Best mobile support.
• Full SQL locally. SQLite on the client means full SQL query capability offline.
• Cloud + self-host. Managed cloud or self-hosted options.

Weaknesses

• More setup. You implement the upload API for handling writes. More control but more work.
• Client SDK is open source, server is commercial. Not fully open-source.
• Sync rules have a learning curve. Defining what data goes where requires understanding the sync rule DSL.
• Server-managed schema. Schema changes require PowerSync Dashboard updates.

Best For

Production apps that need reliable offline sync, especially mobile. Best choice for apps where data access patterns are complex (multi-tenant, role-based).

Zero: Reactive Client Cache

Zero (by Rocicorp, makers of Replicache) is a client-side reactive cache that syncs with any server backend.

How It Works

1. Define queries on the client
2. Zero manages a local cache (IndexedDB)
3. Queries are reactive — UI updates automatically
4. Mutations are optimistic — instant UI response
5. Server confirms or rejects changes

import { useQuery } from '@rocicorp/zero/react';

function TodoList({ projectId, z }) {
  const todos = useQuery(
    z.query.todo
      .where('projectId', '=', projectId)
      .orderBy('createdAt', 'desc')
  );

  const addTodo = () => {
    z.mutate.todo.insert({
      id: nanoid(),
      title: 'New todo',
      projectId,
    });
    // Instantly reflected in UI, synced to server
  };

  return todos.map(todo => <TodoItem key={todo.id} todo={todo} />);
}

Strengths

• Instant UI. Mutations are optimistic. Zero-latency user interactions regardless of network.
• Server-agnostic. Works with any backend (PostgreSQL, MySQL, API). Not Postgres-specific.
• Reactive queries. UI automatically updates when underlying data changes. Similar to Convex's DX.
• Incremental sync. Only syncs changes, not full datasets. Bandwidth efficient.
• Fine-grained reactivity. Only re-renders components whose data actually changed.

Weaknesses

• Newer than PowerSync. Less production-tested at scale.
• IndexedDB limitations. Browser storage limits apply. Not as capable as SQLite for complex queries.
• React-only. No React Native, Flutter, or other framework support yet.
• Server-authoritative. Server is the source of truth. Client changes can be rejected.
• Query language. Custom query builder, not SQL. Less familiar.

Best For

Web apps that prioritize instant UI responsiveness and reactive data. Teams that want local-first benefits without committing to a specific server database.

Feature Deep Dive

Offline Support

PowerSync: Most robust. Full SQLite locally, works completely offline, syncs when reconnected. ElectricSQL: Good offline support via local SQLite/PGlite. Zero: Offline reads from IndexedDB cache. Writes queue and sync on reconnect.

Conflict Resolution

PowerSync: You implement it in your server API. Full flexibility. ElectricSQL: Last-write-wins by default. Simple but may not suit all use cases. Zero: Server-authoritative. Server accepts or rejects mutations.

Performance

Zero: Fastest perceived performance due to optimistic mutations and fine-grained reactivity. PowerSync: Fast local SQLite reads. Upload latency depends on your API. ElectricSQL: Good performance, especially with PGlite for complex local queries.

Pricing

ElectricSQL

• Open source: Free (self-host)
• Cloud: Coming soon (currently self-host only)

PowerSync

• Free tier: 1 app, limited connections
• Pro: From $49/month
• Business: From $199/month
• Self-host: Available

Zero

• Open source: Free (self-host)
• Cloud: TBD

Decision Framework

Choose ElectricSQL if:

• You have an existing PostgreSQL database
• Shape-based sync fits your data access patterns
• You want open-source and self-hosted
• Last-write-wins conflict resolution is acceptable

Choose PowerSync if:

• You need production-proven offline sync
• Mobile support (React Native, Flutter) is important
• You need custom conflict resolution
• Multi-tenant data isolation is critical

Choose Zero if:

• Web-first (not mobile)
• Instant UI responsiveness is the top priority
• You want server-backend flexibility (not just Postgres)
• Reactive queries appeal to your DX preferences

FAQ

Do I need local-first for my app?

If your app needs to work offline, feel instant, or support real-time collaboration — yes. If it's a simple CRUD app that always has connectivity, traditional client-server is simpler.

Can I add local-first to an existing app?

Yes. ElectricSQL and PowerSync are designed to work with existing PostgreSQL databases. Zero works with any backend. All three can be adopted incrementally.

What about CRDTs?

CRDTs (Conflict-free Replicated Data Types) are another approach to local-first sync. Libraries like Yjs and Automerge are best for collaborative text editing. The tools in this comparison are better for structured data (records, rows).

How much data can I sync to the client?

Depends on the platform. SQLite (PowerSync, ElectricSQL) can handle gigabytes. IndexedDB (Zero) is typically limited to hundreds of megabytes. Use partial sync to limit data to what the client actually needs.

The Verdict

• ElectricSQL for the simplest path to local-first with PostgreSQL. Open source and evolving fast.
• PowerSync for production apps, especially mobile. Most mature and battle-tested.
• Zero for the best web DX with instant, reactive UI. Server-agnostic flexibility.

Local-first is still early in 2026, but these tools make it accessible. PowerSync for production confidence, ElectricSQL for PostgreSQL simplicity, Zero for cutting-edge web DX.