HAR Files Explained: The Network Archive Every Developer Should Know

A HAR file is the most information-dense debugging artifact you can include in a bug report. Most developers have never used one. Here's everything you need to know.

What is a HAR file?

HAR stands for HTTP Archive. It's a JSON file that records every network request a browser made during a session — including the method, URL, request headers, request body, response status, response headers, response body, and timing information.

Think of it as a complete transcript of what happened on the wire. Not a summary — the full thing.

{
  "log": {
    "version": "1.2",
    "entries": [
      {
        "startedDateTime": "2026-04-01T14:32:01.000Z",
        "time": 342,
        "request": {
          "method": "POST",
          "url": "https://api.example.com/v1/checkout",
          "postData": { "text": "{\"amount\":NaN}" }
        },
        "response": {
          "status": 500,
          "content": { "text": "{\"error\":\"invalid_amount\"}" }
        }
      }
    ]
  }
}
        

What a HAR file contains that screenshots don't

Request bodies — the exact JSON or form data that was sent to the server
Response bodies — the exact error the server returned
All headers — including auth tokens (redacted), content types, and CORS headers
Timing — DNS lookup, TCP connect, time to first byte, content transfer
Status codes — 401 vs 403 vs 500 are completely different problems
Redirect chains — a 301 that sends somewhere unexpected
All resources — not just failed requests, but every JS/CSS/image load

How to create a HAR file manually

In Chrome:

Open DevTools (F12 or Cmd+Option+I)
Go to the Network tab
Check "Preserve log"
Reproduce the bug
Right-click any request → "Save all as HAR with content"

Firefox and Safari have similar HAR export features in their network panels.

How to open a HAR file in Chrome DevTools

Open DevTools → Network tab
Drag the .har file directly onto the Network panel, or
Click the Import button (↑ icon) and select the file

All requests load immediately. You can filter by type, search by URL, inspect request/response bodies — everything you'd see if you were watching the session live.

Why HAR files are better than "check the console"

"Check the console" requires a developer to reproduce the bug in their environment, which may not match the reporter's environment. A HAR file is a recording of what actually happened, in the actual browser, on the actual machine.

This is especially important for bugs that are environment-specific — different operating systems, different network conditions, different browser versions, different authentication states. If the developer can't reproduce it locally, a HAR file is often the only way to understand what happened.

Privacy considerations

HAR files can contain sensitive data — auth tokens, session cookies, and the contents of API requests and responses. Before sharing a HAR file externally, review it for sensitive headers.

Site Reviewer automatically redacts Authorization, Cookie, and Set-Cookie headers from all captured network entries before they appear in a report or HAR export. Other headers and request bodies are included as-is — review before sharing externally.

HAR vs. screenshots vs. logs

The three main bug report artifacts each tell a different part of the story:

Screenshot — what the user sees (UI state)
Console log — what JavaScript executed and errored
HAR file — what happened on the network

A complete bug report includes all three. Site Reviewer captures all of them automatically — including the HAR export — with a single click.