How to open and run an HTML file (Mac, Windows, and your phone)

Someone sent you a file called index.html. Maybe a developer, maybe an AI, maybe a colleague who swears "it's just a website, open it." You double-clicked and either a page appeared (great, you can stop reading) or a text editor full of angle brackets did (keep reading).

The short answer

An HTML file is a web page that lives on your computer instead of the internet. To see it, open it in a web browser. That's it. No app to install, no "HTML viewer" to download, no account.

On a Mac

1. Find the file in Finder.
2. Right-click it, choose Open With, pick Safari or Chrome.
3. Want it to always open that way? Right-click, Get Info, set Open with to your browser, click Change All.

If it opened in TextEdit, that's your Mac being helpful in the least helpful way.

On Windows

1. Find the file in File Explorer.
2. Right-click it, choose Open with, pick Edge or Chrome.
3. To make it stick: Open with > Choose another app, pick the browser, tick Always use this app.

Notepad opening instead is the Windows version of the TextEdit problem.

The drag-and-drop shortcut (works everywhere)

Open any browser window and drag the file onto it. Done. This is the move to remember.

On an iPhone or Android phone

Phones are bad at this. Tapping an HTML file in Files or a mail attachment usually shows you the code, or a preview with half the page missing.

Your options:

• Put it online first. Upload it to a free HTML to link tool and open the link on your phone. This is the one that actually works.
• Email it to yourself and hope. Results vary from "fine" to "why is everything Times New Roman."

"It opened, but it looks broken"

Usually it's one of these:

• Missing files. The page expects images, CSS or scripts that live next to it in a folder. If someone sent you only the .html, you got the skeleton without the outfit. Ask for the whole folder (zipped).
• Pages that need a server. Some modern apps won't run from your desktop at all. They need to be served from a web address. Uploading them somewhere fixes it.
• Fonts from the internet. Offline? The page will fall back to default fonts and look like it was designed in 2003.

"How do I run it?"

"Running" an HTML file and "opening" it are the same thing. The browser runs any code inside it automatically. If someone tells you to "run it locally," they probably mean opening it in a browser, or they're a developer and you should ask them to just send a link.

If you're opening it to give feedback

This is where most people end up: someone made a page and wants your opinion. Opening the file is step one. Step two is usually a screenshot with a red circle, pasted into an email, describing "the button thing near the top."

There's a better way. Put the page on Kenso and everyone can leave comments right on the parts they mean. No downloading, no red circles, no "which version is this."

Quick recap: drag it into a browser. If it's on your phone, put it online first. If it looks broken, ask for the whole folder.