Migrating from Just

just is a command runner with a Make-like syntax. must provides a superset of just's functionality with language-aware recipes.

Concept mapping

just	must
justfile	Mustfile.toml
recipe_name:	[recipe.recipe_name]
Recipe body (indented)	script = "..."
recipe_name: dep1 dep2	deps = ["dep1", "dep2"]
export VAR := "value"	[env] VAR = "value"
{{ VAR }}	${VAR}
[private]	No direct equivalent — omit from Mustfile
[unix] / [windows]	Use shell conditionals or separate recipes
just --list	must list
just --dry-run	must --dry-run
just --watch	must watch
just recipe_name	must build recipe_name

Side-by-side

justfile:

export OPT_LEVEL := "2"

build:
    cargo build --release

test: build
    cargo test

lint:
    cargo clippy -- -D warnings

clean:
    cargo clean

Mustfile.toml:

[project]
name = "my-app"

[env]
OPT_LEVEL = "2"

[recipe.build]
type    = "rust-bin"
package = "my-app"

[recipe.test]
type    = "rust-test"
package = "my-app"
deps    = ["build"]

[recipe.lint]
type   = "shell"
phony  = true
script = "cargo clippy -- -D warnings"

[recipe.clean]
type   = "shell"
phony  = true
script = "cargo clean"

Key differences

Feature	just	must
Language awareness	No — all recipes are shell	Yes — 41 first-class recipe types
Caching	No built-in caching	Hash/mtime/never per recipe
Cross-compilation	Manual	Automatic with target groups
Dependency graph	Flat	DAG with parallel waves
Plugins	No	Lua plugins with stdlib
Build logs	No	Per-recipe log storage
Outdated checking	No	must outdated

Migration steps

1. Rename justfile to Mustfile.toml
2. Wrap each recipe in [recipe.<name>] with type = "shell"
3. Move exports to [env] section
4. Convert {{ VAR }} to ${VAR}
5. Upgrade shell recipes to first-class types where possible