Install

The decl command ships through four channels. Registry package names differ where decl was already taken; the binary is decl everywhere.

Channel	Install	What you get
npm	npm install -g decl-lang	The TypeScript reference implementation: decl (check, evaluate, validate, fmt) and decl-lsp. Needs Node.js ≥ 22.
PyPI	pip install decl-lang	The native Python implementation: decl (check, evaluate, validate, fmt), decl-lsp, and a Python API. No Node.js.
crates.io	cargo install decl-lang	The native Rust implementation: decl (check, evaluate, validate, fmt) and decl-lsp, no Node or wasm.
Homebrew	brew install luuvish/tap/decl-lang	The npm package through a tap.

All channels produce byte-identical output: the three implementations are held together by a differential test over every example and fixture in the repository — diagnostics, evaluated JSON, formatter output, packages, and a language-server session.

Which one?

• Node.js already around: npm or Homebrew — the reference implementation itself.
• Python projects: PyPI — the same toolchain plus decl.evaluate("site.decl") returning the exported outputs as plain dicts and lists.
• A single static binary for CI, editors, or deployment: crates.io.

From source

git clone https://github.com/luuvish/decl-lang
cd decl-lang
npm install && npm test              # the reference implementation (npm workspaces)
cargo build --release                # the Rust runtime (Cargo workspace)
pip install -e decl-py       # the Python package (builds the grammar extension)
make verify                          # all three, then the parity check

See the tooling pages for each package’s API.