HAR File (HTTP Archive)

A HAR file (HTTP Archive) is a JSON-formatted recording of the network activity a browser captured during a session. It lists each request with its URL, headers, status code, size, and a detailed timing breakdown.

Why it matters

When someone says "your site is slow for me," a HAR file shows exactly what happened on their machine: which request was slow, whether DNS or the server was to blame, and which resources failed. It is the standard way to share a reproducible network trace with support or another developer.

Example

In Chrome, open DevTools, go to the Network tab, tick Preserve log, reload the page, then right-click the request list and choose to save all as HAR. A trimmed entry looks like this:

{
  "request": { "method": "GET", "url": "https://example.com/app.js" },
  "response": { "status": 200, "content": { "size": 184320 } },
  "timings": { "dns": 12, "connect": 40, "ssl": 35, "wait": 310, "receive": 90 }
}

Here wait is roughly the time to first byte for that request.

Common mistakes

• Sharing a HAR publicly without sanitizing it. It can contain cookies, session tokens, authorization headers, and form data. Strip or redact them first.
• Recording with cache enabled and then wondering why requests are missing.
• Reading the total load time instead of the individual timings.
• Capturing with extensions active, which adds unrelated requests.

Related

• Waterfall chart
• TTFB
• Page weight
• Latency

This page is general information written by our editorial team and updated when documentation changes. Servers and providers differ, so test changes safely first. See our editorial policy and disclaimer.