Makefile To Justfile Migration

On this page Overview

Use this when a repo has both Makefile and justfile, or when the user wants to migrate commands from make to just.

Fast Mapping

Make	Just	Notes
`.PHONY: target`	not needed	`just` does not track file timestamps
`.DEFAULT_GOAL := help`	put the default recipe first or use `[default]`	first public recipe is the default
`target: dep1 dep2`	`target: dep1 dep2`	dependency syntax is similar
`@command`	`@command`	suppress command echo
`$(VAR)` / `${VAR}`	`{{var}}`	`just` interpolation
`$$VAR`	`$VAR`	shell vars do not use double-dollar escaping
`VAR := value`	`var := "value"`	quote strings in `just`
`VAR ?= default`	`var := env('VAR', 'default')`	env fallback pattern
`$(shell cmd)`	`cmd`	capture command output
`export VAR := value`	`export var := "value"` or `set export`	export explicitly or globally
`include file.mk`	`import 'file.just'`	import another file

Differences That Matter

Shell Variables

In make, literal shell variables use $$. In just, use $ directly.

target:
	echo $$HOME

target:
	echo $HOME

Recipe Execution Model

Like make, each line runs in a separate shell. Use a shebang recipe when the body must run as one script.

check:
    #!/usr/bin/env bash
    if [ -f .env ]; then
        echo "found"
    fi

Documentation

make often needs a custom help target. In just, the single # comment immediately above a recipe is used by just --list. Keep that documentation as one line; a second comment line above the recipe breaks the preview text.

[private]
default:
    @just --list --unsorted

# Run unit tests
test:
    cargo test

Arguments

just supports recipe arguments directly.

recreate resource:
    terraform apply -replace "{{resource}}"

Migration Checklist

Read the existing Makefile before rewriting anything.
Keep both files during migration if the repo still depends on make.
Convert variables, then recipes, then dependencies.
Replace $$ shell variables with $.
Use a single-line comment above each recipe so just --list stays useful.
Add [confirm] to destructive recipes if the old flow relied on manual care.
Verify migrated commands with just --show <recipe> and targeted dry runs.

Agent Guardrails

Do not suggest migration until you confirm the repo is using just as a real command surface rather than as an experiment.
Watch for make-specific behavior that may not carry over cleanly, such as pattern rules, file-based dependency graphs, or job parallelism.
If both files exist, prefer the one the repo actually documents and uses.