Jess is a native application kernel for Luau applications, built around one rule: policy does not get a privileged native path just because engines traditionally put it there. Packages ship systems and tools. Script domains isolate authority. Capabilities make access explicit. L3i exposes the primitives that genuinely earn the boundary.
That makes it deliberately wider than a game engine. The same runtime hosts command-line tools, long-running applications, servers, build pipelines, and the generator that produced this page.
Where to start§
- New here? Install, write your first script, then build your first package.
- Want the runtime model? Script Domains, Application Kernel, then Packages.
- Building a package? Packages covers Package Sources, JPKs, layers, resolution, and activation; the manifest reference has every key; Capabilities has every name a target can declare.
- Building an application? Applications: managed modules, host callbacks, named events, and interfaces.
- Looking something up? The Luau API Reference and the CLI Reference.
- Working on Jess itself? Contributing covers building, testing, the architecture, and the runtime internals. How decisions are made, who makes them, and what the project commits to is the Constitution.
Architecture in one pass§
| Layer | Job |
|---|---|
| Packages / Luau | Application policy, systems, formats, tools, games, sites, and replaceable implementations. |
| Script domains | Stable identity, lifecycle, workers, resources, deterministic contexts, and explicit authority. |
| Capabilities / IRs | Narrow contracts across boundaries instead of ambient access to an engine singleton. |
| L3i | Lowered operations and native capabilities whose cost model actually justifies native residency. |
| Host | Process integration, platform resources, and the smallest practical privileged surface. |
Opening a package does not secretly start it. A host resolves packages into an activation plan, grants capabilities deliberately, and owns teardown. That distinction, description first, activation second, is what keeps packages composable instead of turning them into another hidden engine lifecycle.
Documentation map§
| Section | What's in it |
|---|---|
| Getting Started | Install, the first package, and an editor that knows the types. |
| Scripting | Scripts, require, the built-in modules, packages, applications, performance, and the Luau pitfalls. |
| Reference | The manifest, every capability, the glossary, and the errors. |
| CLI Reference | Every command and flag. |
| Luau API Reference | Lookup-first module, type, and function reference. |
| Contributing | Building, testing, architecture, script domains, the application kernel, render graph, shader IR, input, localization, and releasing. |
Stability§
Jess is pre-1.0. Runtime APIs, package contracts, CLI surfaces, and native interfaces can change between minor versions. If you build on a moving surface, pin the version and treat your package's tests as part of the contract.