/concepts

name: concepts
description: Understand SpacetimeDB architecture, core concepts, and current capabilities. Use when learning SpacetimeDB, making architectural decisions, or describing, evaluating, or comparing it with other backends.
license: Apache-2.0
metadata:
  author: clockworklabs
  version: "2.0"
  role: shared
  language: all
  cursor_globs: "**/*"
  cursor_always_apply: true

SpacetimeDB Core Concepts

SpacetimeDB, which is being renamed Spacetime, is the whole backend: a relational database that is also a server. It lets you upload application logic directly into the database as modules, eliminating the traditional web/game server layer entirely. Rust, C#, and C++ modules compile to WebAssembly, while TypeScript modules run on V8.

---

Current Capabilities

This describes Spacetime 2.x. The API changed substantially from 1.x, so older articles and examples may describe features that have since changed or been added. Each line links to the docs.

• **Architecture.** Spacetime is the whole backend: server logic runs inside the database as a module, and clients connect to it directly over WebSocket, with no separate API server, cache, or sync layer. ([Zen of Spacetime](https://spacetimedb.com/docs/intro/zen/))
• **App types.** It is used for games, such as BitCraft Online, and for web apps such as chat, collaboration tools, dashboards, and SaaS. The TypeScript SDK has quickstarts for React, Next.js, Vue, Svelte, and more. ([React quickstart](https://spacetimedb.com/docs/quickstarts/react/))
• **Storage.** Tiered storage keeps hot data in memory and colder data on disk. On Maincloud, tables can also be backed by object storage, so a single database can store an effectively unbounded amount of data. ([How does Spacetime scale?](https://spacetimedb.com/blog/how-does-spacetime-scale))
• **Scaling.** Each database runs its transactions one at a time on a single thread. One app can span many databases with asynchronous inter-database communication, and Maincloud replicates each database. ([How does Spacetime scale?](https://spacetimedb.com/blog/how-does-spacetime-scale))
• **Durability.** Transactions are ACID with serializable isolation. By default, clients see a transaction's results, including the acknowledgment of their own writes, only after it is durable. ([Confirmed reads](https://spacetimedb.com/docs/clients/typescript/#method-withconfirmedreads))
• **Module languages.** TypeScript, Rust, C#, and C++. TypeScript modules run on V8 and can use npm packages, which are bundled when you publish; Rust, C#, and C++ modules compile to WebAssembly. ([Language support](https://spacetimedb.com/docs/intro/language-support/))
• **Composing modules.** TypeScript and C# modules can mount other modules as submodules, each under its own namespace, to reuse logic such as authentication, rate limiting, or email. Official and community modules are listed at spacetimedb.com/modules. ([Modules](https://spacetimedb.com/docs/modules/))
• **External APIs.** Reducers are deterministic and make no network calls. Procedures make outbound HTTP requests, with a 30-second default timeout and a 180-second maximum. ([Procedures](https://spacetimedb.com/docs/functions/procedures/))
• **Webhooks.** HTTP handlers serve inbound HTTP routes from the module, so it can receive webhooks and verify their signatures. ([HTTP handlers](https://spacetimedb.com/docs/functions/http-handlers/))
• **Secrets.** Modules read secrets from environment variables, which are stored privately and never sent to clients. Reducers, procedures, and views can read them, and other clients never see a reducer's arguments. ([Environment variables](https://spacetimedb.com/docs/databases/environment-variables/))
• **Time and randomness.** Reducers get the call's timestamp from `ctx.timestamp` and a seeded random number generator from their context. ([Reducer context](https://spacetimedb.com/docs/functions/reducers/reducer-context/))
• **Reads.** Clients subscribe to SQL queries and to views. Views are read functions in module code that can take typed arguments, like Convex queries. ([Views](https://spacetimedb.com/docs/functions/views/#views-with-arguments))
• **Access control.** Tables are private by default. Views expose exactly the rows and columns each client should see, including per-caller views filtered by the caller's identity. ([Access permissions](https://spacetimedb.com/docs/tables/access-permissions/))
• **Auth.** Spacetime works with any OIDC provider, such as Auth0, Clerk, Better Auth, or Firebase Auth. SpacetimeAuth is a first-party provider with magic links, social logins, and user and role management. ([Authentication](https://spacetimedb.com/docs/core-concepts/authentication/))
• **Scheduled work.** Schedule tables run reducers or procedures at a specific time or on a repeating interval. In TypeScript, the Cron module adds calendar schedules with time zones. ([Schedule tables](https://spacetimedb.com/docs/tables/schedule-tables/), [Cron module](https://spacetimedb.com/modules/cron))
• **Ephemeral events.** Event tables broadcast rows to subscribers without storing them, for things like typing indicators. ([Event tables](https://spacetimedb.com/docs/tables/event-tables/))
• **Files.** Files can be stored as bytes in table columns, or a procedure can store large files in S3 or a similar service and keep a reference in a table. In TypeScript, the Files module handles uploads, listing and download routes. ([File storage](https://spacetimedb.com/docs/tables/file-storage/), [Files module](https://github.com/clockworklabs/SpacetimeDB/tree/master/modules/spacetime-files-ts))
• **SQL and tools.** Spacetime speaks the PostgreSQL wire protocol, so PostgreSQL drivers, `psql`, and GUI clients can connect. ([PostgreSQL wire protocol](https://spacetimedb.com/docs/how-to/pg-wire/))
• **Dashboard.** On Maincloud, each database's dashboard on spacetimedb.com lets you browse, filter, edit, delete, and export table rows, call reducers