A HAR file records every request your browser makes when you load a webpage

A HAR file (HTTP Archive) is a text file that captures a complete record of your browser's conversation with web servers. When you visit a website, your browser sends requests for the page itself, images, scripts, stylesheets, and dozens of other resources. A HAR file logs all of those requests and the responses it gets back — what was asked for, when, how long it took, what came back, and whether it succeeded or failed.

The file is formatted as JSON, which is a standard way to structure data that both humans and computers can read. You can open a HAR file in any text editor and see the raw information, though it is usually long and dense. Developers and support teams use HAR files to diagnose why a website loads slowly, why a feature is broken, or why a user is seeing an error that nobody else can reproduce.

The main reason HAR files matter is that they show the exact sequence of events. A developer can see not just that something failed, but when it failed, what caused it to fail, and what else was happening at the same time. This is much more useful than a user saying "the website is slow" or "the login button doesn't work."

Key Takeaways

  • A HAR file records every request and response between your browser and web servers, including timing and success or failure status.
  • Developers use HAR files to diagnose performance problems, broken features, and errors that are hard to reproduce.
  • You can record a HAR file using your browser's built-in developer tools — usually by opening the Network tab, performing an action, and exporting the results.
  • HAR files contain sensitive information like cookies, authentication tokens, and URLs you visited, so you should review them before sharing with support teams.
  • A HAR file is most useful when it captures the exact moment a problem occurs, so timing matters more than file size.

How to record a HAR file in your browser

Every modern browser has built-in developer tools that can record a HAR file. The steps are similar across Chrome, Firefox, Safari, and Edge, though the exact menu names differ slightly.

In Chrome or Edge, right-click anywhere on the webpage and select "Inspect" or "Inspect Element." This opens the developer tools panel. Click the "Network" tab. Now reload the page or perform the action that is causing the problem — log in, click a button, upload a file, whatever you need to test. The Network tab will fill with a list of requests. Once you have finished, right-click anywhere in that list and select "Save all as HAR with content." Choose where to save the file.

In Firefox, the process is the same: right-click and select "Inspect," click the "Network" tab, perform your action, then right-click in the Network list and select "Save All As HAR." Safari requires you to enable the developer menu first (Preferences > Advanced > Show Develop menu in menu bar), then use Develop > Show Web Inspector, click the Network tab, and right-click to save.

The file will be named something like archive.har and will be a few hundred kilobytes to a few megabytes depending on how much activity happened. A HAR file recorded over 30 seconds of normal browsing is usually enough to diagnose a problem.

What information a HAR file contains

A HAR file includes the URL of every resource loaded, the HTTP method used (usually GET or POST), response codes (like 200 for success or 404 for not found), response headers, response body content, and precise timing data showing how long each request took and where the time was spent — waiting for the server to respond, downloading the data, or processing it.

It also records cookies, which are small files your browser stores to remember you. If you are logged into a website when you record the HAR file, your authentication token or session ID will be in the file. This is why you should never share a HAR file publicly or with someone you do not trust. A person with your HAR file could potentially use the cookies in it to access your account on that website.

Before you send a HAR file to a support team or post it in a public forum, open it in a text editor and search for sensitive terms like "password," "token," "authorization," or "cookie." You can delete those lines or replace the values with fake data. Most support teams understand this and will ask you to sanitize the file before sending it.

Why developers ask for HAR files instead of screenshots

A screenshot shows what you see on the screen at one moment. A HAR file shows what your browser was doing behind the scenes. If a page loads slowly, a screenshot cannot tell you whether the delay was caused by a slow server, a large image file, a third-party ad network, or your own internet connection. A HAR file shows all of that.

HAR files are also reproducible. If you send a support team a HAR file, they can examine the exact same data you saw, in the exact same order, without having to ask you to repeat the steps or try to guess what went wrong. This is especially useful for problems that happen only sometimes or only under certain conditions.

The other reason is that some problems are invisible in the browser. A request might fail silently, or a server might return an error code that the page hides from you. A HAR file reveals those hidden failures.

Common reasons developers request a HAR file

Support teams ask for HAR files most often when a website is loading slowly, a feature is broken only for you, or an error message appears that does not appear for other users. They also request HAR files when a payment or login fails, when a file upload does not work, or when a page works in one browser but not another.

If you are reporting a problem and a support team asks for a HAR file, it usually means they cannot reproduce the problem on their end and need to see the exact sequence of requests and responses that happened on your computer. This is not a sign that you did something wrong — it is a sign that the problem is specific to your situation, your network, or your browser setup, and the HAR file is the best way to diagnose it.

Sometimes a support team will ask you to record a HAR file while you perform a specific action, like logging in or uploading a file. In those cases, start recording before you begin the action and stop recording after it completes. The smaller and more focused the HAR file, the easier it is to read.

The difference between a HAR file and browser cache or cookies

A HAR file is a snapshot of network activity — a record of what happened during the time you were recording. Browser cache and cookies are stored files that your browser keeps on your computer to make websites load faster and remember you.

Cache stores copies of images, scripts, and stylesheets so your browser does not have to read them again. Cookies store small pieces of data like your login information or your preferences. Neither of these is a HAR file. A HAR file is created only when you explicitly record it using developer tools, and it disappears when you delete it. Cache and cookies persist until you clear them or they expire.

If a support team asks you to clear your cache or cookies, that is a different troubleshooting step from recording a HAR file. Clearing cache and cookies can fix problems caused by outdated stored data. Recording a HAR file helps diagnose problems that are happening in real time.

When a HAR file is not helpful

A HAR file is most useful for problems that happen consistently and involve network requests. If a problem happens only once a month, or only on a specific date, or only after you have been using the website for hours, a single HAR file might not capture it. In those cases, a support team might ask you to record multiple HAR files over time or to describe the exact conditions when the problem occurs.

A HAR file is also less useful for problems that are purely visual — like a button being the wrong color or text being cut off. Those problems are usually easier to diagnose from a screenshot. However, if a visual problem is caused by a missing or broken resource (like an image that failed to load), a HAR file will show that the resource request failed.

If you are unsure whether to record a HAR file, ask the support team. They will tell you whether it will help or whether they need different information.

Frequently Asked Questions

Can I open a HAR file myself to see what is in it?

Yes. A HAR file is plain text formatted as JSON, so you can open it in any text editor like Notepad or Word. It will be long and hard to read, but you can search for specific terms. Some websites like www.softwareishard.com/blog/har-viewer/ provide online HAR viewers that format the data more readably, though you should not upload sensitive HAR files to public websites.

Is it safe to share a HAR file with a support team?

It is usually safe if you review the file first and remove sensitive information like cookies, passwords, or authentication tokens. Most support teams understand that HAR files contain sensitive data and will ask you to sanitize them. Never post a HAR file in a public forum or share it with someone you do not trust.

How long should I record a HAR file for?

Record long enough to capture the problem — usually 30 seconds to a few minutes. Longer recordings create larger files that are harder to read and may include unrelated activity. Start recording just before you perform the action that causes the problem and stop just after it completes.

What if the support team says my HAR file is too large?

Large HAR files usually mean you recorded for too long or the website loaded a lot of resources. Try recording again, but this time perform only the specific action that is broken and stop when ready after. If the file is still large, ask the support team which part of the file they need to see.

Do I need to know how to read a HAR file to send one to support?

No. You just need to know how to record it. The support team will read and interpret the file for you. Your job is to record the file while the problem is happening and send it to them. They will use it to diagnose what went wrong.