---
title: "What is the muse CLI?"
url: https://helicon.sh/glossary/muse-cli
description: "The muse command line tool is how you run Muse Code. What it installs, what muse login does, and why a GUI still needs it present."
updated: 2026-09-19
site: Helicon
---

# What is the muse CLI?

The muse CLI is the command line tool that runs Muse Code. You install it, authenticate once with `muse login`, and then run `muse` inside a project to start a session. It holds your credentials, and every graphical client for Muse Code, including Helicon, drives this CLI rather than replacing it.

## The commands that matter

| Command | What it does |
| --- | --- |
| muse | Starts an interactive session in the current directory |
| muse login | Authenticates you. Credentials stay with the CLI |
| muse serve | Starts a protocol host that other applications can drive |
| muse --version | Confirms the install is present and reachable |

## Why a GUI still needs it

A client like Helicon has no model, no account and no credentials. It starts `muse serve` and speaks the protocol to it, which means the agent, the subscription and the login are all the CLI's. If `muse --version` does not answer, the GUI has nothing to talk to.

## Where credentials live

With the CLI, from your own `muse login`. Helicon never stores or handles them, which is the answer to the most common security question about wrapper clients.

## Frequently asked questions

### Do I need the CLI if I use a GUI?

Yes. Every Muse Code GUI drives the CLI. It is a requirement, not an alternative.

### What does muse serve do?

It starts a host that speaks the Muse Code Session Protocol over JSON-RPC, which is how applications drive a session properly.

### Where does muse login store credentials?

With the CLI itself. Clients like Helicon read nothing and store nothing.

## Related

- [muse serve](https://helicon.sh/glossary/muse-serve): muse serve starts a Muse Code protocol host that applications can drive over stdio. What it is for, and how a GUI uses one host per workspace.
- [the Muse Code Session Protocol](https://helicon.sh/glossary/msp): MSP is the JSON-RPC protocol that applications use to drive a Muse Code session over stdio, instead of parsing terminal output. What it carries and why it matters.
- [Fix: muse CLI not found](https://helicon.sh/guides/muse-cli-not-found): Helicon needs a working, logged in muse CLI. Here is how to check which install it is looking at on Windows, macOS, Linux and WSL2, and how to fix each case.

---

Helicon is a free, MIT licensed, unofficial community client for Meta's Muse Code CLI. Not made, sponsored or endorsed by Meta. Source: https://helicon.sh/. Machine readable index: https://helicon.sh/llms.txt