Convex — the reactive TypeScript backend

• Source: https://www.convex.dev/ (sent by owner, 2026-09-02)
• Verdict: promote-to-dev
• Why: the backend that makes the happy path the correct path. You write query/mutation/action functions in a convex/ folder as plain TypeScript, they execute as serializable transactions (optimistic concurrency on an append-only transaction log) directly inside the database, and useQuery subscriptions push updates over WebSocket whenever a read set is invalidated. Document-relational, schemaless on day one but defineTable/defineSchema gives you incremental rigor, file storage/search/vector search/crons/scheduling/auth built in. Built by Dropbox ex-infra founders Jamie Turner (CEO) and James Cowling (CTO, MIT PhD distributed transactions) who shipped multi-exabyte storage — that discipline is the product: end-to-end types, automatic caching/scaling, zero manual sync.

Convex open-sourced its backend in Feb 2025 (Rust + TS, ~12k stars) under FSL-1.1-Apache-2.0 — source-available, no competing hosted offer, auto-converts to Apache-2.0 two years after each release; cloud runs on PlanetScale/MySQL, self-host can use SQLite/Postgres/MySQL but hosted dashboard/CLI is where most tooling lives. Architecture is three pieces: sync worker (WebSocket sessions), function runner (V8, bundled via esbuild), and database (transaction log + multiversion indexes + subscription manager) — How Convex Works is the deep dive. Pricing is generous free (1M calls, 0.5 GB DB) then Pro $25/developer/month (not flat) + usage, Enterprise from $2,500/mo with SOC 2 Type II/HIPAA/RBAC/SSO; that per-developer shape is the gotcha vs Supabase's flat $25. Funded to $110.5M total after the $57M Series B on 2026-08-04 led by Insight Partners (a16z, Spark, Etna Labs, Justin Kan) — powers ~2M apps for ~500k devs, 1.2M weekly npm downloads, used by OpenAI/Zapier/Tripadvisor/Solana. Its pitch for the agent era is blunt: 90% of AI-built apps on traditional DBs silently corrupted data in Convex's testing vs 0% on Convex, because reactive serializable transactions make the first thing an agent writes also the safe thing.

Worth filing in Development next to the other backends — if this site ever needs live sync without wiring WebSockets by hand, this is the one to promote. Compare Firebase (fastest on-ramp, proprietary, per-read bills with no cap, no self-host) and Supabase (flat $25, real Postgres/Apache-2.0, self-host yes) for the usual tradeoff triangle.

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.