Install Plain

You can try Plain in your browser right now, with nothing to install: open the playground, pick an example and press Run.

Install Plain on your computer when you want to keep your programs and data files there, or have Plain ask Claude for ideas. It takes about 15 minutes. You don't need to know anything about programming.

You'll type a few commands into a window called Terminal (on a Mac) or PowerShell (on Windows). A command is a line of text that tells your computer what to do. Type each one exactly as shown, or copy it from this page and paste it. Then press Return (Mac) or Enter (Windows). Nothing happens until you do.

Install on a Mac

You'll install three things: Python, the free program Plain runs on; pipx, a helper that installs programs like Plain; and Plain itself.

1. Open Terminal. Press Command+Space, type Terminal and press Return. A window opens with a line that ends in %. This is where you type commands. Leave it open.

2. Download Python. Go to python.org/downloads and click the yellow Download Python button. Any version from 3.13 up works.

3. Install Python. Open the file you downloaded. You'll find it in your Downloads folder. Click Continue and Agree until you can click Install. Your Mac may ask for the password you use to log in.

4. Install the web certificates. When the installer finishes, a Finder window opens. Double-click Install Certificates.command in it. This lets Plain check that websites are who they say they are. A Terminal window shows a few lines and ends with [Process completed]. You can close that window.

5. Check Python. Quit Terminal (press Command+Q) and open it again, so it finds the new Python. Then type:

python3 --version

You should see Python and a version number, like Python 3.15.1. If your Mac offers to install "command line developer tools" instead, click Cancel and go back to step 2.

6. Install pipx. Type:

python3 -m pip install --user pipx

You'll see several lines while it works. The last one may be a warning that pipx is "not on PATH". PATH is the list of places your computer looks for commands. That's fine: the next step adds pipx to it.

7. Tell Terminal where pipx is. Type:

python3 -m pipx ensurepath

It says it added a folder to your PATH, and that you need to open a new terminal.

8. Install Plain. Quit Terminal and open it again. Then type:

pipx install plainlang

After a moment, it lists plain as a new command and says done!

9. Check Plain. Type:

plain --version

You should see Plain and a version number, like Plain 0.1.0. Plain is installed.

Run your first program on a Mac

1. Open TextEdit. Press Command+Space, type TextEdit and press Return. Click New Document.

2. Make it plain text. Choose Make Plain Text from the Format menu. Plain can't read the rich text TextEdit uses at first.

3. Type this line:

show "Hello there!"

4. Save it. Choose Save from the File menu. Name it hello.plain, choose Documents as the place, and click Save. If TextEdit asks which ending to use, click Use .plain.

5. Run it. In Terminal, type these two commands, one at a time:

cd Documents
plain run hello.plain

The first command moves Terminal into your Documents folder, where you saved the file. The second runs your program. You should see:

Hello there!

You've written and run a program. Next, try the lessons.

Install on Windows

You'll install three things: Python, the free program Plain runs on; pipx, a helper that installs programs like Plain; and Plain itself.

1. Open PowerShell. Press the Windows key, type PowerShell and press Enter. A window opens with a line like PS C:\Users\Ann>. This is where you type commands.

2. Download Python. Go to python.org/downloads and click the yellow Download Python install manager button.

3. Install Python. Open the file you downloaded. You'll find it in your Downloads folder. Click Install.

4. Check Python. Close PowerShell and open it again. Then type:

python --version

The first time, Python may ask you a few yes or no questions. Type y and press Enter for each one. Be sure to say yes to Install CPython now? CPython is Python itself. If a window opened by itself after step 3 and asked these questions, answer them there the same way.

When it's done, you should see Python and a version number, like Python 3.15.1. Any version from 3.13 up works. If you don't see it, type python --version again. If the Microsoft Store opens instead, Python isn't installed yet: go back to step 2.

If you used the standalone installer instead (the link under the yellow button), tick Add python.exe to PATH on its first screen before you click Install Now.

5. Install pipx. Type:

python -m pip install --user pipx

You'll see several lines while it works. The last one may be a warning that pipx is "not on PATH". PATH is the list of places your computer looks for commands. That's fine: the next step adds pipx to it.

6. Tell PowerShell where pipx is. Type:

python -m pipx ensurepath

It says it added a folder to your PATH, and that you need to open a new terminal.

7. Install Plain. Close PowerShell and open it again. Then type:

pipx install plainlang

After a moment, it lists plain as a new command and says done!

8. Check Plain. Type:

plain --version

You should see Plain and a version number, like Plain 0.1.0. Plain is installed.

Run your first program on Windows

1. Open Notepad. Press the Windows key, type Notepad and press Enter.

2. Type this line:

show "Hello there!"

3. Save it. Choose Save as from the File menu. Choose Documents on the left. Type hello.plain as the file name, and set Save as type to All files. If there's an Encoding choice, leave it on UTF-8. Click Save.

4. Open PowerShell in your Documents folder. Open File Explorer and go to Documents, where you saved the file. Click the address bar at the top, type powershell and press Enter. A new PowerShell window opens, already in that folder.

5. Run it. In the new window, type:

plain run hello.plain

You should see:

Hello there!

You've written and run a program. Next, try the lessons.

If something goes wrong

Find the message you see, then follow the fix.

• "command not found: plain" (Mac) or "The term 'plain' is not recognized" (Windows). Close Terminal or PowerShell and open it again. If you still see it, run step 7 (Mac) or step 6 (Windows) again, then close and open the window again. On Windows, restarting your computer can also help.
• "command not found: pipx" or "The term 'pipx' is not recognized". Type python3 -m pipx (Mac) or python -m pipx (Windows) where the steps say pipx. For example: python3 -m pipx install plainlang.
• "Check the file name "hello.plain". There's no file with that name here." Terminal or PowerShell is in a different folder from your file, or the file has a different name. Type ls (Mac) or dir (Windows) to list the files in the folder. If you see hello.plain.txt, your editor added .txt to the name. Rename it with mv hello.plain.txt hello.plain (Mac) or ren hello.plain.txt hello.plain (Windows).
• Plain's message mentions words like "rtf1" or "fonttbl". TextEdit saved your file as rich text. In TextEdit, choose Make Plain Text from the Format menu, then save again.
• "Save "hello.plain" as plain text (UTF-8), then try again." Save the file again, and choose UTF-8 as the encoding.
• "Install your computer's web certificates, then run this again." On a Mac, open your Applications folder, open the Python folder in it, and double-click Install Certificates.command.

If you're still stuck, see Get help.

Ask Claude for ideas (optional)

Plain can ask Claude, an AI made by Anthropic, for ideas when it can't follow a line. You don't need this to use Plain. Without it, Plain still offers its own ideas.

You need two things:

• An Anthropic account. Sign up at platform.claude.com. Anthropic charges your account a small amount for each request, so set up billing in your account first.
• A key. A key is a secret code that lets Plain use your account. In your account, go to Settings, then API keys, and create a key. Copy it right away: it starts with sk-ant-, and Anthropic shows it only once. Keep it secret, like a password.

Then follow these steps.

1. Install Plain with Claude's help included. Type:

pipx install "plainlang[ai]"

If you've already installed Plain, add --force so pipx replaces it:

pipx install --force "plainlang[ai]"

2. Save your key where Plain looks for it. Plain looks for your key in a setting called ANTHROPIC_API_KEY. In the command below, put your key in place of paste-your-key-here, and keep the quotes.

On a Mac, type:

echo 'export ANTHROPIC_API_KEY="paste-your-key-here"' >> ~/.zshrc

On Windows, type:

setx ANTHROPIC_API_KEY "paste-your-key-here"

3. Close Terminal or PowerShell and open it again. Now, when you use plain run or plain fix and Plain can't follow a line, it tells you it's asking Claude:

Asking Claude for ideas. This sends hello.plain to Anthropic, which charges your account a small amount for each request.

Claude's ideas come after Plain's own, marked (from Claude).

Here's what Plain does to keep you in charge:

• Plain checks every idea from Claude before it shows it to you, and leaves out any idea that doesn't work.
• Plain changes your file only when you choose an idea, and keeps your old file in a copy that ends in .bak.
• Plain sends the lines of your program, after hiding anything that looks like a password or a key. It never sends your data files or the answers you type.
• Plain asks Claude only when you run it in Terminal or PowerShell. It never asks in plain check or in the playground.

To turn it off for one run, add --no-ai:

plain run hello.plain --no-ai

To turn it off every time, set PLAIN_AI to off, then close the window and open it again. On a Mac, type:

echo 'export PLAIN_AI=off' >> ~/.zshrc

On Windows, type:

setx PLAIN_AI off

Choose a text editor

Any text editor works. Save each program as plain text, with a name that ends in .plain.

• On a Mac, TextEdit works. Choose Make Plain Text from the Format menu for each new file. To make every new file plain text, choose Settings from the TextEdit menu, and under Format choose Plain text.
• On Windows, Notepad works. When you save, set Save as type to All files, or Notepad may add .txt to the name.
• A free code editor, such as Visual Studio Code, shows line numbers. They match the line numbers in Plain's messages.

Don't write programs in Word, Pages or Google Docs: they save hidden formatting that Plain can't read. Text you copy from them is fine. Plain reads “curly quotes” the same as "straight quotes".

To move a line to the right, under an if or a repeat, type 4 spaces or press Tab. Plain treats a Tab the same as 4 spaces.

If plain starts a different program

Another program called Plain, a tool programmers use to build websites, also installs a command named plain. If you have it, plain may start that program instead of this one, or pipx may say a file named plain already exists.

You can still use this Plain. Install it straight into Python, then type python3 -m plainlang (Mac) or python -m plainlang (Windows) wherever this site says plain. On a Mac:

python3 -m pip install --user plainlang
python3 -m plainlang run hello.plain

On Windows:

python -m pip install --user plainlang
python -m plainlang run hello.plain

Update or remove Plain

To get the newest version of Plain, type:

pipx upgrade plainlang

To remove Plain from your computer, type:

pipx uninstall plainlang