• Small, fast, static binary.
• Shuts down each command if one fails. No more processes clinging to ports.
• Supports running npm scripts and binaries.
• Labels output for each command.

On macOS, you can install with:

brew install rosszurowski/tap/tandem

If you have Go installed, you can install from the source with:

go install github.com/rosszurowski/tandem@latest

If you're using tandem from a Makefile, this snippet shows how to download a locally cached copy.

Use tandem by passing a set of commands to run in parallel. Wrap each command in quotes, like so:

tandem 'command1 "arg"' 'command2 "arg"' 'command3 "arg"'

Working on a Next.js app, you might want to run your front-end dev server alongside a backend API server with live updating changes through nodemon:

$ tandem 'next dev' 'nodemon --quiet ./server.js'
next     ready - started server on 0.0.0.0:3000, url: http://localhost:3000
next     event - compiled client and server successfully in 15 ms (25 modules)
nodemon  starting server...
nodemon  listening on http://localhost:3001

If your scripts are defined in package.json, you can reference them by using npm: as a prefix:

{
  "scripts": {
    "dev:php": "...",
    "dev:js": "...",
    "dev:css": "..."
  }
}

$ tandem 'npm:dev:php' 'npm:dev:js' 'npm:dev:css'

Wildcard rules like npm:dev:* are also supported as a shortcut. This line is equivalent to the above:

$ tandem 'npm:dev:*'

In a Makefile, use this snippet to fetch a local copy for your project. Change the .cache path as needed, and add it to your .gitignore.

dev: node_modules .cache/tandem
	@.cache/tandem 'command1' 'command2'
.PHONY: dev

.cache/tandem:
	@mkdir -p $$(dirname $@)
	@curl -fsSL https://raw.githubusercontent.com/rosszurowski/tandem/main/install.sh | bash -s -- --dest="$$(dirname $@)"

Running make dev will download tandem once, and then use it for every run from there on out.

I regularly use Makefiles to automate project commands and tools. Makefiles are mostly great! But their biggest failing (also a failing of shells generally) is that it's shockingly hard to coordinate multiple commands as one group:

• make -jN <a> <b> <c> doesn't end all tasks when another one fails. For running local dev servers, this means you can lose your CSS or JS watcher and not realize.
• command1 & command2 & wait often leaves commands hanging around in the background, which is annoying when it eats up a port you want to use.
• Tools like GNU parallel have a confusing syntax, and I've never been able to figure out how to stop all tasks when one fails.

tandem makes running concurrent servers easy. It takes inspiration from concurrently or npm-run-all, but improves performance and works as a static binary.

tandem owes a big thanks to hivemind, from which much of the source is drawn. tandem can be thought of as a fork of hivemind, but rather than defining commands in a Procfile, defining them from a list of arguments.

tandem's illustration was drawn by Hannah Lee.