j3c <command> [file.j3 | project]
A path can be a .j3 file, a j3.toml, or a directory containing one. With no path, j3c uses ./j3.toml.
| Command | Does |
|---|
j3c new <name> | New console project (--app for a window, --template fps or --template ui) |
j3c guide | How to start a project |
j3c check | Type-check without building. --json prints one JSON object. |
j3c run | Build and run. --file f.j3 runs one file inside a project. |
j3c run tool.j3s [args] | Run a script’s pub fn main once |
j3c build | Build target/<name> |
j3c size | What is inside the binary: sections, code per module, biggest functions |
These work with run and build, and override j3.toml.
| Flag | Effect |
|---|
--release | Smallest binary: opt s, no debug info, stripped. Checks stay on. build also writes packages. |
--fast | Removes bounds-check aborts and debug info |
--opt N | 0, 1, 2, 3, s, or z |
--emit llvm|c | Pick the backend |
| Flag | Effect |
|---|
--headless | No window and no sound (SDL offscreen) |
--frames N | Stop after N frames |
--screenshot f.png | Save the last frame |
--hot | Rebuild and restart when a source file changes |
See Testing Headless.
| Command | Does |
|---|
j3c fmt [path] | Print formatted source. --write rewrites files, --check fails if any would change. |
j3c lsp | Language server over stdio |
j3c doc ... | Stdlib docs, guides, and recipes (see below) |
| Command | Shows |
|---|
j3c doc | Tasks and the list of stdlib modules |
j3c doc <module> | A module’s public items (--short for one screen) |
j3c doc search <word> | Public names containing a word |
j3c doc lang | Language summary |
j3c doc recipes [name] | Complete example programs |
j3c doc j3ui, css, testing, ship, threads, android | Guides |
j3c help manifest | Every j3.toml key |
| Command | Prints |
|---|
j3c dump-ir | The checked IR |
j3c dump-llvm | LLVM IR |
j3c dump-c | C source |
j3c dump-ui <file.j3ui> | J3 generated from a UI component |
j3c dump-bc <file.j3s> | Script bytecode |
j3c dump-syntax | A TextMate grammar for editors |
| Command | Does |
|---|
j3c editor [project] | Open the 3D scene editor |
j3c -e scene <op> | List, get, add, set, delete, or check scene objects |
j3c -e render | Draw a scene to a PNG without a window |
j3c -e gen | Run mesh generators in assets/gen/ that changed |
j3c -e mcp | MCP server, so AI agents can edit and render scenes |
j3c golden <dir> | Headless golden-image tests |
j3c -e imgdiff a.png b.png | Pixel diff two images |
j3c version --verbose prints the build, the stdlib source, and the binary path, which helps spot a stale j3c on your PATH.