Overview

Tandem is a sync engine and database for collaborative apps. Each client keeps a local database that the UI reads from directly. Writes apply locally right away, and Tandem syncs them with a server in the background.

Why

Collaborative apps need a few things at once:

Writes that show up in the UI immediately
Changes from other clients that appear without a reload
A consistent result when clients edit the same data at the same time
Something sensible to do when the network is slow or unavailable

Tandem handles these in the data layer, so app code can read and write local data without managing requests.

Components

`TandemClient`

TandemClient is the app-facing API from @tanishqkancharla/tandem-core. It exposes:

query and subscribe for typed object queries
transact and commit for writes
connect, disconnect, and pullFromRemote for sync control

Local database

The local database stores records as ordered tuples. It evaluates queries in memory and can persist to IndexedDB through TandemClientIndexedDbStorage.

Sync engine

The sync engine runs when a client has a remote. It pushes local mutations, pulls patches for the queries the client subscribes to, and rebases pending local mutations on top of each patch. See How sync works.

Remote

A remote implements the RemoteApi contract: connect, push, and pull. TandemServer from @tanishqkancharla/tandem-server implements it directly. In a browser app, a small HTTP or RPC transport on the client forwards calls to it. See Server and Custom remotes.

Current limitations

Conflicts resolve as last write wins per record. There are no field-level merges or intents.
Server sync metadata lives in memory and resets when the server process restarts.
There is no schema versioning or migration story for persisted client storage.

See the Roadmap for planned work.