Convex — the reactive TypeScript backend

Filed from Convex — the reactive TypeScript backend.

What it is

Convex is a backend where your database queries are TypeScript functions that run inside the database as serializable ACID transactions, and the results sync to clients live over WebSocket. You write query / mutation / action functions in a convex/ folder; useQuery subscriptions push updates whenever a read set is invalidated. No SQL, no ORM, no glue code, no hand-wired WebSockets.

The data model is document-relational: schemaless on day one, with defineTable / defineSchema when you want incremental rigor. File storage, full-text and vector search, crons, scheduling, and auth are built in rather than bolted on.

Why it's interesting

The founders are ex-Dropbox infra — CEO Jamie Turner and CTO James Cowling (MIT PhD, distributed transactions), people who shipped multi-exabyte storage. That discipline is the product: end-to-end types, optimistic concurrency on an append-only transaction log, automatic caching and scaling. The happy path is the correct path, which matters more than usual right now: Convex's pitch for the agent era is that 90% of AI-built apps on traditional databases silently corrupted data in their testing, versus 0% on Convex — because reactive serializable transactions make the first thing an agent writes also the safe thing.

The backend open-sourced in February 2025 (Rust + TypeScript) under FSL-1.1-Apache-2.0 — source-available, no competing hosted offer, auto-converting to Apache-2.0 two years after each release. Self-hosting can run on SQLite, Postgres, or MySQL.

Where it bites

• Pricing is per developer, not flat. The free tier is generous (1M calls, 0.5 GB), then Pro is $25/developer/month plus usage. Compare Supabase's flat $25. Teams feel this shape immediately.
• FSL is not open source. Source-available with a two-year fuse to Apache-2.0. Fine for most people, a dealbreaker for some — know which you are.
• The hosted dashboard is where the tooling lives. Self-hosting is real, but the gravity pulls toward their cloud.
• Funded to $110.5M after a $57M Series B in August 2026 led by Insight Partners. Money is not a technical argument, but it predicts which docs stay maintained.

The tradeoff triangle

• Firebase: fastest on-ramp, proprietary, per-read billing with no cap, no self-host.
• Supabase: flat $25, real Postgres, Apache-2.0, self-host yes.
• Convex: reactive sync and transactions as the default, per-dev pricing, source-available.

If this site ever needs live sync without wiring WebSockets by hand, this is the one to promote.

Verdict

The rare backend where the marketing claim ("no glue, just types") survives contact with the architecture docs. Worth a real look the next time a project needs realtime without the realtime tax.

Virelai for Convex

Refrain — sung before and between each verse

No glue, just types — the query lives where data lives — — convex! — What changes once, all clients know it gives.

I.

You write no SQL, no ORM to chase or shive — A A convex/ of functions, pure query in light — b Mutations close as transactions, serializable and right — b OCC upon a log that never needs contrive — a

No glue, just types — the query lives where data lives — — convex!

II.

The sync worker watches, the runner seals to thrive — A V8 bundled by esbuild, sandboxed and contrived to hold — b Indexes multiversioned, read-sets quietly told — b WebSockets whisper useQuery till the view's alive — a

What changes once, all clients know it gives.

III.

Dropbox exiles built it for exabyte archive — A FSL now, Apache later — two years till laws forgive — b Twenty-five per dev, not flat — the price will test the sieve — b Yet agents write the first thing safe, and safe will live — a

No glue, just types — the query lives where data lives — — convex! — What changes once, all clients know it gives.