If you're building an app that needs to feel instant and keep working when the wifi drops, you'll eventually run into "local-first" — data lives on the user's device and syncs in the background instead of the app waiting on a network round-trip for every click. InstantDB and ElectricSQL both solve this, but they start from opposite ends: InstantDB is a full database (with auth, storage and permissions built in), while ElectricSQL is a sync engine that sits on top of a Postgres database you already have.
The short version: pick InstantDB if you're starting a new app and want one tool to handle data, auth, storage and real-time sync together. Pick ElectricSQL if you already run Postgres and just need to make an existing database sync to the client without rebuilding your backend.
InstantDB: a modern, open-source Firebase
InstantDB is a real-time database with auth, storage and permissions built in — data lives on the client and syncs instantly across users and devices, similar to what Firebase does but open source (Apache 2.0). It's local-first AND relational, so you get instant/offline reads with real relationships instead of a flat document store. The free tier is genuinely usable: unlimited API calls and 1GB storage, then Pro is $30/month for 10GB (plus $0.125/GB after), Startup $600/month for 250GB, Enterprise custom with SLAs.
Good for: frontend and full-stack developers and small teams building real-time, multiplayer or offline-capable apps who want one tool instead of stitching together a database, an auth provider and a sync layer.
Limits: it's younger than Firebase or Supabase, so the ecosystem and large-scale track record are thinner. The client-first model suits interactive apps more than heavy server-side or analytics workloads, and migrating away is non-trivial once your app logic is tied to InstaQL and its permission model.
ElectricSQL: sync for the Postgres you already have
ElectricSQL keeps a live copy of your Postgres data on each user's device, so the app feels instant and keeps working offline instead of waiting on the network for every action. Rather than replacing your database, it rides on top of it — sync travels over plain HTTP with CDN caching, which scales cheaper than a websocket-per-user backend, and it works with any frontend framework since your source of truth stays plain Postgres. The open-source core is free to self-host; Electric Cloud is usage-based at roughly $1 per 1M writes pay-as-you-go, dropping to $0.90/1M on the $249/month Pro plan and $0.80/1M on the $1,999/month Scale plan, with unlimited reads and concurrent users.
Good for: developers who already have a Postgres database and want to make an existing app local-first or real-time without a backend rewrite.
Limits: local-first is still an emerging paradigm, so patterns are less battle-tested than a plain REST API. It only syncs Postgres — not a fit if your source of truth is a different database — and a recent rebrand from electric-sql.com to electric.ax means some older docs and tutorials point to the wrong place.
Side by side
| InstantDB | ElectricSQL | |
|---|---|---|
| What it is | Full database (data + auth + storage + permissions) | Sync engine on top of your existing Postgres |
| Starting point | New app, no existing database required | You already run Postgres |
| Pricing | Free (1GB), $30/mo Pro (10GB) | Free self-hosted core, ~$1/1M writes on Cloud |
| Open source | Yes (Apache 2.0) | Yes (Apache 2.0 core) |
| Also compare against | Firebase, Supabase, Convex | PowerSync, Zero (Rocicorp), Convex |
Neither is a drop-in replacement for the other, which makes the choice fairly mechanical: if you're greenfield and want fewer moving parts, InstantDB gets you a working backend today. If Postgres is already your source of truth and the only thing missing is instant, offline-capable sync to the client, ElectricSQL adds that layer without asking you to migrate your data model anywhere.