If you've ever used an app that feels instant — no spinner when you click a button, no "please wait" when your wifi drops — there's a good chance it's built on what developers call a local-first approach. Instead of every action waiting on a round trip to a server, the app keeps a live copy of your data right on your device and quietly syncs it in the background. When it works well, you never notice it. When it's missing, you notice immediately (that little lag before a button click "takes").
This guide looks at four real, currently-used tools that developers reach for when building this kind of experience: ElectricSQL, InstantDB, Convex, and Turso. They're not interchangeable — each solves a slightly different piece of the "make my app work instantly and offline" problem — so we've broken down who each one is actually for.
The short version
| Tool | What it actually is | Best for | Pricing |
|---|---|---|---|
| InstantDB | Real-time database with built-in auth, storage & permissions | Frontend/full-stack teams building multiplayer or offline-capable apps | Free tier (1GB), Pro from $30/mo |
| ElectricSQL | Sync engine that mirrors your existing Postgres onto each device | Teams who already run Postgres and want to add local-first sync on top | Not public |
| Convex | Reactive backend platform (functions + database) that keeps clients in sync | Developers who want a full reactive backend, not just a sync layer | Not public |
| Turso | Edge-distributed SQLite — a drop-in SQLite replacement you can deploy close to users | Teams wanting SQLite's simplicity, deployed globally at the edge | Not public |
InstantDB — the most "batteries-included" option
InstantDB bundles database, authentication, file storage and permissions into one tool, aiming to be what a modern, open-source Firebase would look like. Reads are local-first and relational, meaning you get real relationships between your data (not just flat key-value blobs) while still getting instant, offline-capable reads.
Forces: one tool covers the whole stack (DB, auth, storage, real-time sync); it's open source (Apache 2.0) instead of Firebase's proprietary lock-in; and the free tier is genuinely usable — unlimited API calls plus 1GB of storage to launch on.
Limites: it's younger than Firebase or Supabase, so the ecosystem and track record at large scale are thinner. It also leans client-first, which suits interactive, multiplayer-style apps more than heavy server-side analytics — and once your app's logic is wired into its InstaQL query language and permission model, migrating away isn't trivial.
Pricing: free tier with unlimited API calls and 1GB storage; Pro at $30/mo (10GB, then $0.125/GB beyond); Startup at $600/mo (250GB); custom Enterprise with SLAs.
ElectricSQL — sync for teams already on Postgres
ElectricSQL takes a different angle: instead of replacing your database, it keeps a live copy of your existing Postgres data on each user's device. If your backend already runs on Postgres, this is the option that lets you add local-first behavior without a rewrite — your app feels instant and keeps working offline, but the source of truth stays exactly where it already is.
Its own comparison data lists InstantDB as a direct alternative — worth knowing if you're deciding between "sync an existing Postgres database" (ElectricSQL) versus "start fresh with an all-in-one real-time database" (InstantDB).
Convex — a full reactive backend, not just sync
Convex markets itself as a backend platform that "keeps your app in sync" — but it's broader than a sync engine. It combines a database with server-side functions, and the reactive part means your UI updates automatically whenever underlying data changes, without you writing manual refetch logic. Its stated strengths are simplified state management and easy integration for developers who want to skip building that reactive plumbing themselves.
Watch for: pricing isn't fully public and the platform is less widely known than Firebase or Supabase in general developer circles — worth a closer look at current docs before committing a production app to it.
Turso — SQLite, but distributed to the edge
Turso takes yet another approach: it's built as a full replacement for SQLite that you can deploy flexibly across multiple locations, positioning itself for the kind of "copy of the database everywhere" architecture that AI agents and edge-deployed apps increasingly need. If your app (or your team's mental model) is already SQLite-shaped, Turso lets you keep that simplicity while distributing data close to users instead of running a single centralized instance.
Watch for: like Convex, pricing detail is thin publicly, and it's a newer name in the market than the SQL databases most teams default to.
Which one should you actually pick?
Rough rule of thumb: if you already run Postgres and just want to add offline/instant behavior on top, start with ElectricSQL. If you're starting a new app from scratch and want auth, storage and real-time sync in one open-source package, InstantDB's free tier is worth prototyping on directly. If what you actually want is a reactive backend (functions + data, not just a sync layer), look at Convex. And if you specifically want SQLite's simplicity deployed at the edge, Turso is the closest match.
None of these tools have fully transparent public pricing beyond InstantDB, so budget time to actually talk to sales or test the free tiers before committing — "local-first" is a fast-moving space in 2026, and the right pick depends more on what you're already running than on any one tool being objectively "best."