SDK Concepts

App

An app is a builder-owned unit that Space can launch through an entrypoint such as space -m main. An app usually brings its own assets, code, lifecycle hooks, and user-facing commands, then asks the host for the capabilities it needs.

Host

The host is the Space runtime process that loads an app, resolves assets, exposes runtime facets, runs the scheduler, and reports failures when required inputs or capabilities are missing.

Capability

A capability is a named contract an app or extension expects the host to provide. Capabilities should make required inputs explicit and fail loudly when unavailable. Common capability areas include commands, input, presentation, scene, metadata, and inspectors.

Runtime Facet

A runtime facet is one builder-facing surface of the host, such as scheduler, input, presentation, scene, asset loading, or command registration. Facets group related operations so an app can request only the host behavior it needs.

Modules vs. App Contracts

Modules are reusable Space ecosystem libraries that builders import directly. Use the module reference to find canonical import names, APIs, examples, aliases, and platform notes.

App contracts describe how an app talks to the Space host. Use the app/host reference for app module shape, host capabilities, runtime facets, commands, scene access, packaging, and graph extension descriptors.

Command

A command is an invocable action exposed by an app, extension, or host facet. commands should document required arguments, expected results, and failure behavior so malformed invocations are visible during development.

Scene Capability

A scene capability lets an app create or update spatial objects, world views, and scene-backed presentation. Builders use it when app state needs to appear in the 3D scene rather than only in non-spatial UI.

Graph Extension Unit

A graph extension unit is a packaged addition to Space's graph-oriented environment. It can contribute graph behavior, metadata, inspectors, commands, or presentation surfaces while keeping graph internals in the developer docs.

Package

A package is the distributable shape of an app, extension, widget, world, workflow, or independent application. A package should include the assets, entrypoints, metadata, and host requirements needed to run predictably.

Example

An example is a copyable starting point that demonstrates a focused app shape or capability in context. Examples are not a substitute for reference contracts, but they show how lifecycle, assets, presentation, scene behavior, and commands fit together.

Next Steps

• Reference — look up current contracts and required inputs.
• Guides — solve task-focused builder problems.
• Developer Docs — read internals and maintenance details when SDK pages link deeper.