What is a CLI (command line interface)?

The first time I looked up "command line interface," I learned it was something you use inside a terminal—that window where developers type inscrutable commands in a pixelated-looking font. Right then and there, I dismissed the command line as something that only capital-d developers could use.

Then vibe coding tools started blurring the line between who's technical and who isn't, and I started to flirt with the idea of learning CLI again. What I discovered is that it's not as intimidating as I'd made it out to be. You certainly don't need a computer science degree to use it. You can grasp the basics in a few days and feel genuinely comfortable with it in a month or two—enough to back up your files to the cloud, auto-convert new image files to JPG, and do so much more in your other apps without leaving the terminal.

In this guide, I'll walk you through what a CLI actually is and why you might want to use it. Plus, I'll compare it with two other initialisms you might be hearing about a lot right now: MCP and SDK. By the end, you'll know enough to dabble in the CLI world yourself and use it to securely run actions across thousands of apps through Zapier.

Table of contents:

• What is a CLI?

• Why use a CLI over a GUI?

• How does a CLI work?

• Common CLI commands

• MCP vs. SDK vs. CLI: What's the difference?

• Run actions across 9,000+ apps with the Zapier CLI

What is a CLI?

A CLI, or command line interface, is a text-based method for "talking" to your computer. You type a command, hit enter, and your computer completes your request.

Compare that to a GUI, or a graphical user interface. That's what most of us use every day. A GUI is a visual way of interacting with your computer, through things like windows, icons, menus, and buttons you click. When you drag a file into a folder, double-click an app to open it, or hit a button to save a document, you're communicating with your computer through a GUI.

Here's a folder that contains images for a blog post I wrote. To interact with an image, I have to click its name or its thumbnail. To move between folders, I have to click the back and forward arrows in the title bar. 

Now here's a list of those same images in a terminal. To manipulate these, I'd need to use text-based commands. There's nothing I can click here.

Both a GUI and a CLI let you take the same actions, like creating files, moving them around, running programs, and changing settings on your computer. The difference lies in the method of communication.

Why use a CLI over a GUI?

A GUI is more intuitive because it's visual. But a CLI is actually faster and more flexible once you've got some commands down, because typing a single line can do what would take a dozen clicks in a GUI.

For example, if you needed to rename 500 client invoice PDFs with the invoice date pulled from inside each file, you could do it by hand…if you wanted to give your fingers a solid workout. Or you could just run one CLI command and be done in seconds.

Here's where CLIs come in handy—and in some cases, where they're the only option:

• Handling repetitive tasks. Anything you'd have to do over and over in a GUI can usually be done with a single CLI command. You can also set groups of commands to run on a schedule or trigger other actions.

• Controlling remote servers. Most remote servers—the computers in data centers that run websites, databases, and scheduled jobs—don't have a graphical interface at all. A CLI is the only way in.

• Working with more technical tools. Lots of tools are designed to be run from a terminal. If you want to clone a project from GitHub, set up a coding assistant like Claude Code, or use the Zapier CLI, you'll need to do it from the terminal.

The terminal is the connective tissue across a lot of technical work, and getting comfortable there opens up tools that would otherwise be off-limits. 

How does a CLI work?

To use a CLI, you open a program called a terminal. On Mac, it's an app literally called Terminal. On Windows, it's Command Prompt or PowerShell.

When you open a terminal, you'll see a window like this. 

Let's break down what we're looking at in that screenshot.

The title bar at the top shows the current folder you're working in, followed by the name of the shell you're running—in my case, Zsh (pronounced Z-shell, or "zeesh"). A shell is just a program that interprets the commands you type and passes them to your computer. After the shell name, you'll see your window size in characters—mine is 80 columns wide, 24 rows tall. That actually matters because some terminal programs format their output based on how wide the window is. If the numbers are distracting, you can hide them in your terminal settings.

The first line inside the window shows your last login time and a string like ttys0000. That's the name of the connection between you and the shell. The s0000 part means it's the first shell tab you've opened. Open another and you'll see ttys0001, and so on. It's a handy reference when you're juggling multiple projects in different tabs.

The most important part of this screen, though, is the final character in the last line. That % (sometimes it looks like $ or >) is called the shell prompt. It's a symbol that the terminal produces to tell you that it's ready for input. After each shell prompt, you can type an instruction called a command and hit enter. The shell—again, that's the engine that runs the terminal—then interprets your command and delivers the message to your computer. 

Which commands you use will depend on which shell you're running. For example, Mac and Linux both descend from an older operating system called Unix, built at Bell Labs in 1969 and foundational to most of modern computing. Because they share that Unix ancestry, they also share the same shells. Windows wasn't built on Unix, so it has its own.

Here are the most popular shells:

• Bash: The long-standing standard on most Linux systems. It was also the default on Mac until 2019, and you can still run it there.

• Zsh: This is the default shell on newer Macs, having taken over from Bash in 2019. It's also available on Linux.

• Command Prompt: The older default shell on Windows.

• PowerShell: Microsoft's more modern Windows shell, with more capabilities than Command Prompt.

The shell isn't permanently locked to the OS. You can install other shells onto your computer if you want. Running Bash on Windows, for example, is possible through Windows Subsystem for Linux (WSL)—a tool that lets you run a Linux environment inside Windows—or through a smaller tool called Git Bash that ships Bash on its own.

Every shell has dozens of built-in commands, and many of them overlap from one shell to the next. So if you know Bash, a lot of what you know carries over to Zsh. Command Prompt and PowerShell on Windows use different command names for some of the basics, but the concepts are the same.

Common CLI commands

You don't need to know every command within a shell to be productive. And gratefully, many of the commands are abbreviated versions of what they represent, like cd for "change directory," which makes learning them easier.

Here are a handful that'll cover the most common use cases:

• pwd (print working directory): Shows you which folder you're currently in.

• ls (list): Lists the files and folders in whichever folder you're in.

• cd (change directory): Moves you into a different folder. cd Documents moves you into the Documents folder, and cd .. moves you up one level.

• mkdir (make directory): Creates a new folder. mkdir projects creates a folder called projects.

• touch: Creates a new empty file. touch notes.txt creates an empty file called notes.txt.

• cp (copy): Copies a file from one place to another. cp file.txt backup.txt makes a copy called backup.txt.

• mv (move): Moves or renames a file. mv file.txt new-name.txt renames it, and mv file.txt Documents/ moves it.

• rm (remove): Deletes a file. Be careful with this one—there's no recycle bin to recover from. rm file.txt is a permanent action.

• cat: Prints the contents of a file directly into the terminal. This is good for quickly reading short files.

• echo: Prints whatever you type back to the screen, which is useful for testing and for writing into files.

• man (manual): Shows the documentation for any command. man ls tells you everything ls can do.

As you get deeper into learning the command line, you'll pick up two related concepts: options, which are additions to a command that modify its behavior, and arguments, which are the files, folders, or programs a command acts on.

The terminal also has a few keyboard shortcuts worth knowing. 

• Tab autocompletes file and folder names based on what's in your current folder, so you don't have to type things out (or risk misspelling them). 

• The up arrow cycles through your recent commands. 

• Ctrl+C cancels whatever's currently running. 

• Ctrl+L clears the terminal.

You can also save a sequence of commands into a text file (usually ending in .sh) to run the whole operation at once. That's called a shell script, or just script. So instead of typing these commands and hitting enter one at a time:

mkdir projects

cd projects

touch notes.txt 

…you can save those three lines to a file called setup.sh and run it with one command. 

If you feel like you're being walloped by tech lingo here, take heart—you don't need to memorize a million commands to be able to use a CLI. There are plenty of cheatsheets online that list everything for a given shell. And if you're ever unsure about what to type, remember that you can always ask AI. Just describe what you're trying to do, and you'll get a command you can paste into your terminal. 

Just be careful. Commands can permanently delete files, change system settings, or do other things that are hard to reverse. So read what you're pasting before you run it, and if you don't understand a command, ask AI for a translation.

MCP vs. SDK vs. CLI: What's the difference?

If you're researching CLIs right now, there's a good chance you've also run into the terms MCP and SDK. They're related, but they're different tools. I find that the easiest way to keep them straight is to think about who they put in the driver's seat.

• The CLI (command line interface) is a text-based way to control your computer by typing commands into a terminal. A CLI puts you in the driver's seat. You type precise commands, deciding exactly what runs and what data goes into it.

• MCP (model context protocol) is an open standard that lets AI tools like Claude and ChatGPT connect to other apps. MCP puts an AI tool in the driver's seat. You tell AI what you want in plain English, and the AI figures out what to do and how to do it.

• An SDK (software development kit) is a collection of tools, libraries, documentation, code samples, and APIs bundled together to help people build applications for a specific platform, framework, or service. An SDK puts your code in the driver's seat: you write a program that calls on the SDK to handle complex tasks. That way, you can focus on building the bigger piece of software around it.

It's worth noting that with AI coding tools like Cursor and Claude Code, you don't need to be a developer to use an SDK. If you're comfortable with vibe coding, you can describe what you want to build and have the AI write the implementation code that calls the SDK for you. You'll still need a project set up and enough understanding to know if the code is doing what you asked, but the bar to entry is so much lower than it used to be.

Run actions across 9,000+ apps with the Zapier CLI

Once you're comfortable in a terminal, you can use the Zapier CLI to build safely across more than 9,000 apps without ever leaving your terminal.

What the Zapier CLI actually does

Let's look at it using an example. Normally, if you wanted to write a script that creates a row in Google Sheets, you'd have to handle authentication yourself. That entails:

1. Creating a project in Google Cloud Console

2. Turning on the Sheets API for that project

3. Setting up credentials and downloading a file with secret keys

4. Writing code that exchanges those keys for an access token

5. Attaching that token to every request and refreshing it when it expires

And all of that has to happen before the first row of data ever gets created. And it's per app. You'd repeat this process for Slack, Notion, Salesforce, and every other tool you want to script against. What should be a quick automation can balloon into hours, sometimes days, of setup that has nothing to do with the work you actually want to do.

What Zapier does is handle all of that once, when you connect an app in your Zapier account. After that, anything built on top of Zapier—in the Zap editor, Zapier MCP, the CLI, the SDK—just uses that connection. You never have to deal with auth code, ever.

Say you want to add a new contact to HubSpot. Zapier gives you three ways for making that possible:

• With Zapier MCP: You'd tell Claude or ChatGPT, "Add Marcus Chen as a contact in HubSpot. He's a marketing director at XYZ company." The AI picks the right action and maps your sentence to HubSpot's fields. There's no need to know what the action is called or what inputs it expects.

• With the Zapier SDK: That same action lives inside your software. Say your company has an internal form for sales reps to enter new leads. The SDK is what lets the form, when submitted, automatically call HubSpot's Create Contact action behind the scenes. There's no copy-pasting and no manual entry. It's an invisible bridge between your tool and HubSpot.

• With the Zapier CLI: In your terminal, you'd type a command that names the action and lays out each input explicitly: first name Marcus, last name Chen, company XYZ, job title Marketing Director. There's more setup than MCP, but in exchange, you get precision. The same command run twice produces the exact same result, every time. (With MCP, the AI is interpreting your request, so it might map "marketing director at XYZ" to slightly different fields depending on how you phrase it or which AI you're using. The CLI removes that variability.)

What you can do with Zapier CLI

A few things the Zapier CLI is good for:

• Exploring what an integration can do. Run npx zapier-sdk list-actions slack (or any other app name) and you get the full menu of available actions in your terminal. Run another command to see exactly what inputs each action needs, like required and optional fields. You could find some of this on Zapier's integration pages, but the CLI gives you discovery and documentation all in one place. The full list of available commands lives in the Zapier CLI docs.

• Scripting workflows. Once you know what actions exist and what they need, you can chain them together in a shell script. For example, you can pull yesterday's sales from a Google Sheet, format the data, post a summary to Slack, then archive the result to Notion. You can package those four actions together in a single file and run them at any time.

• Scheduling recurring work. If you hand that script to your operating system's scheduler (cron on Mac/Linux, Task Scheduler on Windows), it'll run automatically. For example, every Monday at 8 a.m., your weekly sales summary could post to Slack without you doing a thing. This is one place the CLI has an edge over MCP, which is built for on-demand requests, not scheduled work.

• Debugging. If you built a Zap and it's not behaving—say, rows are showing up in your Google Sheet with empty columns—the CLI lets you call the same action by hand with the exact inputs you expect, so you can see what comes back. It's how you figure out exactly where a workflow is actually broken.

What you'll need to know

To use the Zapier CLI, you need:

• Node.js and npm installed. Node.js is the runtime, which is just software that lets your computer execute the CLI's code. npm is the package manager that comes with it and is what you'll use to install the CLI itself. You can download both from nodejs.org.

• Basic terminal skills. You'll need to be comfortable navigating directories (cd, ls) and running commands. If you got through the sections above, you're set. A handful of shell commands is all you really need to get started.

• A basic understanding of JSON. JSON (JavaScript Object Notation) is a format for structuring data. When you pass inputs to a Zapier action—like the first name and email of a new contact—you do it in JSON. It looks like this: {"first_name": "Marcus", "email": "marcus@xyz.com"}. The curly braces mark the start and end of the data. Between the curly braces, you list out your data. Each item has three parts: a label in double quotes ("first_name"), a colon, and the value (also in double quotes if it's text). That's most of what you need to know. You can learn enough JSON to be functional in about half an hour.

Installing the CLI is quick. Once Node.js and npm are set up, you run a single npm install command to add it to your system, then authenticate with your Zapier account. From there, you can start calling actions.

The Zapier CLI and Zapier SDK are built to work together. A common path is to explore in the CLI first—run commands, see what an integration can do, and then prototype a workflow as a shell script. Plenty of scripts are fine to live in the CLI forever, like a personal automation or a script your team runs internally. But if a script needs to become part of a real software product, you can port it to the SDK without starting over. 

Talk directly to your computer with CLI

The terminal has a reputation for being the developer's domain. But it's really just another way to talk to your computer—one that happens to be faster, more precise, and more automatable compared to clicking through menus. Arm yourself with a handful of commands and a willingness to read what you're typing before you hit enter, and you'll be well on your way.

Once you're in, the command line becomes a kind of universal remote. You can chain commands into scripts, schedule those scripts to run on their own, log in to servers you'll never physically touch, and reach for tools that don't have a visual interface at all. And Zapier MCP, the Zapier SDK, and the Zapier CLI are three ways to bring all of that into the places you already work with AI.

Related reading:

• What is MCP (Model Context Protocol)?

• Zapier SDK: Connect your code files to thousands of actions

• Zapier MCP, Zapier SDK, and Zapier CLI: What's the difference?