HARpoon
HAR files, explained

What is a HAR file?

A HAR file (HTTP Archive) is a JSON file that records every network request a web page made while it loaded — every URL, HTTP status, request and response header, timing, and transfer size, in the order they happened. Browsers export it from their DevTools, and it's the standard way to capture exactly what a page did on the network so someone else can diagnose a slow load or a failing request without being at your machine.

What's inside a HAR file?

A HAR is a single JSON object with a list of entries — one per request. Each entry records the request (method, URL, headers, query string, and any posted data), the response (status, headers, content type, size, and optionally the body), and a detailed timing breakdown: how long the request spent blocked, in DNS, connecting, negotiating TLS, waiting for the first byte, and receiving data. It also notes which requests went to third-party domains. Add it all up and you can reconstruct the entire load — which is why it's so useful for finding what made a page slow.

How to export a HAR file

Every major browser exports a HAR from its DevTools Network panel. Reload the page while recording so the whole load is captured, then save.

Google Chrome

  1. Open DevTools: press F12, or Ctrl+Shift+I (Windows/Linux) / ⌘+⌥+I (macOS).
  2. Click the Network tab.
  3. Tick "Preserve log" if the page redirects or you need to navigate while recording.
  4. Reload the page (Ctrl/⌘+R) so the full load is captured.
  5. Right-click any request in the list and choose "Save all as HAR with content".
  6. Save the .har file somewhere you can find it.

Microsoft Edge

Edge shares Chromium DevTools, so the flow matches Chrome.

  1. Open DevTools with F12 or Ctrl+Shift+I / ⌘+⌥+I.
  2. Open the Network tab and enable "Preserve log" if needed.
  3. Reload the page to record the full load.
  4. Right-click a request and choose "Save all as HAR with content" (or use the download-arrow "Export HAR" icon).

Mozilla Firefox

  1. Open DevTools: F12, or Ctrl+Shift+E (Windows/Linux) / ⌘+⌥+E (macOS) to jump straight to Network.
  2. Reload the page so the requests are recorded.
  3. Right-click any request and choose "Save All As HAR" — or use the gear/settings menu in the Network panel and pick "Save All As HAR".

Safari

You need the Develop menu first.

  1. Enable web-developer features: Safari → Settings → Advanced → tick "Show features for web developers" (older versions: "Show Develop menu in menu bar").
  2. Open the Web Inspector: Develop → Show Web Inspector, or ⌘+⌥+I.
  3. Select the Network tab and reload the page.
  4. Click the Export button (the export icon in the Network tab toolbar) and save the .har file.

Before you share a HAR: the privacy warning

A HAR can contain secrets. Treat it like a password.

Because a HAR records real requests, it captures whatever those requests carried: cookies, Authorization headers, session tokens, API keys in URLs or headers, form data, and query-string values. If you exported with response content, it may also contain the bodies of API responses — including personal data. Anyone with your HAR can potentially replay your session.

  • Only capture the page you actually need, and reload just before exporting.
  • Where your browser offers "export without content", prefer it if you don't need response bodies.
  • Scrub cookies and auth headers before posting a HAR in a public issue or support ticket.
  • Never share a HAR from a logged-in banking, admin, or production session publicly.

When you analyze a HAR with Harpoon, the file is used to compute the findings and score; the optional AI explanation is generated only from those curated findings and page metadata — never from your raw requests, cookies, tokens, or response bodies.

Try it

Got a HAR? See what's slow.

Drop it below to open the request waterfall and get a ranked, quantified list of what's slowing the page down. Free, no signup.

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Exported from Chrome DevTools → Network → Save all as HAR
First time? Export a capture from your browser's DevTools

HAR file FAQ

What does HAR stand for?

HAR stands for HTTP Archive. It is a JSON-based file format, originally from the web performance community, for recording the network activity of a web page.

How do I open or read a HAR file?

A HAR is plain JSON, but it is hard to read by hand. Drop it into a HAR viewer to see the requests as a sortable waterfall with timings, sizes, and status codes — much easier than scrolling raw JSON.

Is it safe to share a HAR file?

Only with care. HAR files can contain cookies, authorization headers, tokens, and query-string values that let someone replay your session. Scrub sensitive data first, export without response content when you can, and never post a HAR from a logged-in production session publicly.

What are HAR files used for?

Diagnosing web performance and network problems: figuring out why a page is slow, which requests are heavy or blocking, why a resource failed, and proving a fix worked by comparing a before/after capture.