A HAR file is a record of everything your browser downloaded to load a webpage

HAR stands for HTTP Archive. When you visit a website, your browser makes dozens or hundreds of requests — for the HTML page itself, images, scripts, stylesheets, fonts, and other files. A HAR file logs all of those requests and responses in a single text file that you can open and read.

The file contains timestamps, file sizes, load times, headers, and the actual content that moved between your computer and the web server. It looks like structured data (because it is — it's formatted in JSON), but the important part is that it captures a complete snapshot of what happened during a specific browsing session.

HAR files are most useful when something goes wrong. If a webpage loads slowly, partially, or not at all, a HAR file shows exactly where the delay happened — whether the server was slow to respond, whether a particular image failed to read, or whether a script crashed before finishing. Web developers and support specialists ask for HAR files because the file tells them what they cannot see from their own computer.

Key Takeaways

  • A HAR file records every request your browser made and every response it received while loading a webpage, including timing and file sizes.
  • You create a HAR file by opening your browser's developer tools, starting a recording, visiting the webpage, and then saving the log as a .har file.
  • HAR files are most valuable when you are troubleshooting a problem — they show a support specialist exactly where a page failed or slowed down.
  • A HAR file may contain passwords, session tokens, or other sensitive data if you were logged into accounts during recording, so review it before sharing.
  • Different browsers store HAR files in different locations, but all modern browsers (Chrome, Firefox, Safari, Edge) can create them through the developer tools.

Why you might need to create a HAR file

You create a HAR file when you need to show someone else — usually a support specialist or web developer — exactly what your browser experienced. If a page loads slowly only for you, or if it fails to load certain elements, a HAR file proves what happened and when.

Support teams use HAR files to rule out problems on your end. If your internet connection is fine and your computer is not overloaded, but a page still loads in 45 seconds instead of 5, the HAR file will show whether the delay is on the server side, the network side, or caused by a particular resource (like a large video or a slow third-party script) that is blocking the page.

You might also create a HAR file to document a problem before reporting it, or to compare how a page loads at different times of day or from different networks. Some websites ask for a HAR file in their troubleshooting steps.

How to create a HAR file in Chrome or Edge

Open the webpage where you are experiencing the problem. Then press F12 (or Ctrl+Shift+I on Windows, Cmd+Option+I on Mac) to open the developer tools. Click the Network tab at the top.

You will see a circle icon in the upper left of the Network panel — make sure it is red (recording). If it is gray, click it to start recording. Now reload the page by pressing F5 or Ctrl+R. Wait for the page to finish loading completely. Once it has, right-click anywhere in the Network panel and select Save all as HAR with content. Choose where to save the file on your computer.

The file will be named something like www.example.com.har. This is a plain text file, but do not try to edit it — open it only to view it or to send it to someone who asked for it.

How to create a HAR file in Firefox

Open the webpage and press F12 (or Ctrl+Shift+I on Windows, Cmd+Option+I on Mac) to open the developer tools. Click the Network tab. Reload the page by pressing F5 or Ctrl+R and wait for it to load completely.

Right-click in the Network panel and select Save All As HAR. Choose a location on your computer and name the file. Firefox will save it as a .har file that you can share or review.

How to create a HAR file in Safari

Safari's developer tools are hidden by default. Go to Safari menu → Preferences → Advanced tab, and check the box that says Show Develop menu in menu bar. Close Preferences.

Now open the webpage and click Develop in the menu bar → Show Web Inspector. Click the Network tab. Reload the page and wait for it to load. Right-click in the Network panel and select Export HAR. Choose where to save the file.

What a HAR file contains and privacy concerns

A HAR file contains the URL of every resource loaded, the time each request took, the size of each file, HTTP headers, and response codes. It may also contain the actual content of those resources — images, scripts, and text.

The important privacy point: if you were logged into an account when you recorded the HAR file, the file may contain session tokens, authentication cookies, or other data that could let someone else access your account. Before you send a HAR file to anyone, open it in a text editor and search for sensitive information like passwords, API keys, or personal data. Delete or redact those lines before sharing.

Most support specialists know to ask you to review the file first, but it is your responsibility to check. If you are not sure whether something in the file is sensitive, do not share it — ask the person requesting it whether they need that particular section.

How to read a HAR file

A HAR file is formatted as JSON, which means it is structured but human-readable if you know what you are looking at. You can open it in any text editor — Notepad, Word, VS Code, or whatever you have. The file will show entries for each request, with fields like startedDateTime (when the request began), time (how long it took in milliseconds), request (what was asked for), and response (what came back).

You do not need to understand every field. If you are sending the file to a support specialist, they will read it. If you are reading it yourself to troubleshoot, look for entries with large time values (those are slow requests) or entries with response codes in the 400s or 500s (those are errors). A response code of 200 means the request succeeded; 404 means the file was not found; 500 means the server had a problem.

Frequently Asked Questions

Can I create a HAR file on my phone or tablet?

Mobile browsers have limited developer tools. On iPhone, you can use Safari's remote debugging through a Mac, but it is complicated. On Android, Chrome has a mobile developer mode, but creating a full HAR file is not straightforward. For most phone issues, describe the problem to support and they may ask you to test on a desktop browser instead.

How big is a typical HAR file?

A HAR file for a straightforward webpage might be 100 kilobytes. A complex page with many images, videos, or third-party scripts can be several megabytes. If your HAR file is very large, you can compress it as a .zip file before sending it to someone.

Will creating a HAR file slow down my browser or use a lot of data?

Recording a HAR file does not use extra data — it just logs what your browser is already downloading. It may use a tiny amount of memory while the developer tools are open, but not enough to notice on a modern computer.

Can I delete a HAR file after I create it?

Yes. A HAR file is just a record of what happened during one browsing session. Once you have sent it to someone or reviewed it, you can delete it. If you need another one, you can create a new one by repeating the steps.

What if the person asking for a HAR file wants me to record a specific action, like logging in or clicking a button?

Start the recording in the Network tab before you do the action. Perform the login, click the button, or do whatever they asked you to do. Then stop recording and save the file. This captures exactly what happened during that action, which is more useful than a general page load.