HAR File Viewer Online - TestMu AI (Formerly LambdaTest)

What is a HAR file?

A HAR file, short for HTTP Archive, is a JSON log of a browser session's network activity. It records every HTTP request and response the page made, along with the request and response headers, query strings, cookies, payloads, status codes, and detailed timing for each call. The format is standardized, so a HAR captured in one browser opens cleanly in another tool.

HAR files are generated from the browser developer tools. When you open the Network tab in DevTools and reload a page, the browser records the full request waterfall. Exporting that capture writes it to a .har file you can save, share, and replay later. Because a HAR is plain JSON, it is portable evidence of exactly what a user's browser sent and received during a session.

How to use the HAR file viewer?

Inspecting a capture takes only a few seconds, and you do not need to install anything. Follow these steps to view and analyze a HAR file:

• Export the HAR: Open browser DevTools, go to the Network tab, reload the page, and use Export HAR or Save All As HAR to write the capture to disk.
• Upload the HAR file: Drag the .har file into the viewer or click the dropzone to browse and select it from your machine.
• Browse the requests: Scroll the request list to find specific URLs, status codes, or resource types in the capture.
• Inspect a request: Click any request to see its headers, request and response bodies, cookies, query strings, and timing breakdown.
• Filter and search: Use the controls to narrow the list by HTTP method, status code, resource type, or a URL substring.
• Analyze the timings: Use the timing waterfall to spot slow DNS, TLS, time to first byte, or content download phases.

What the HAR file viewer shows

As a tool, the HAR file viewer surfaces everything stored inside a capture in a familiar DevTools-style layout. Here is what the viewer renders for each load:

• Request List and Split View: Every request appears in a scrollable list, with a full inspector beside it so you can read details without losing your place.
• Headers and Cookies: Request and response headers, cookies, and query strings are shown per request, so you can confirm exactly what was sent and returned.
• Status Codes and Methods: Each entry shows its HTTP method and status code, making failed, redirected, and blocked requests easy to spot at a glance.
• Response and Request Bodies: JSON, HTML, and text bodies are rendered in the inspector, with pretty printing for JSON so API responses are readable.
• Timing Waterfall: Blocked, DNS, connect, TLS, send, wait (TTFB), and receive phases are plotted on a timing bar for fast visual triage.
• Filters and Size Metrics: Type, status, method, and URL filters narrow the list, while transferred and resource sizes help you find heavy payloads.

How to capture a HAR file from your browser

A HAR file is produced from the browser developer tools, not from this viewer. The steps differ slightly per browser, but the pattern is the same: open DevTools, record the Network tab, reload, then export. Here is how to capture one in the major browsers:

• Chrome, Edge, and Brave: Press F12, open the Network tab, reload the page to record the requests, then click the download icon and choose Save all as HAR with content.
• Mozilla Firefox: Press F12, open the Network panel, reload the page, then open the gear menu in the top right of the panel and select Save All As HAR.
• Apple Safari: Enable the Develop menu in settings, open the Network tab in Web Inspector, reload the page, then use the Export button at the top of the panel.
• Preserve and disable cache: Before reloading, enable Preserve log and Disable cache so navigation requests and uncached assets are recorded in full.

Use cases of the HAR file viewer

A HAR capture is useful anywhere you need to see exactly what a browser sent and received. The viewer speeds up each of these developer and QA workflows by rendering the capture for you:

• Customer Bug Reproduction: Ask a user to attach a HAR and replay exactly what their browser saw, with no screen share or remote access needed.
• API Failure Debugging: Confirm request URLs, payloads, and response status codes when an endpoint misbehaves, and pair the check with the View Page Source tool to inspect the rendered markup.
• Performance Triage: Identify slow time to first byte, blocked requests, and oversized payloads using the timing waterfall and size metrics.
• Pre-Release QA: Compare HARs before and after a deploy to catch new third-party calls, regressions, or unexpected error responses.
• Test Data Preparation: Generate edge-case fixtures for negative testing with the Corrupt File Generator, then verify how your app handles malformed responses.
• Security Review: Audit which headers, cookies, and data a page sends to third parties before sharing a capture externally.

This viewer is maintained by TestMu AI (formerly LambdaTest), the team behind a unified testing platform, so it is shaped by the same focus on reliable, performance-tested web apps that QA and SDET engineers depend on. For related debugging work, the JSON Validator helps you confirm that API response bodies pulled from a HAR are well formed before you act on them.

Frequently Asked Questions (FAQs)

What is a HAR file?

A HAR (HTTP Archive) file is a JSON log of a browser session's network activity. It records every HTTP request and response with its headers, payloads, cookies, status codes, and timing data, exported from the browser DevTools Network panel.

Is the HAR file viewer free to use?

Yes, the HAR file viewer is completely free with no signup, login, or usage limit. Upload any .har export and inspect as many requests as you need. The tool is maintained by TestMu AI (formerly LambdaTest).

Is my HAR file uploaded to a server?

No. The HAR file is parsed entirely in your browser and nothing is uploaded. Sensitive headers, cookies, auth tokens, and request bodies inside the file never leave your machine, which keeps captures private.

How do I generate a HAR file from my browser?

Open DevTools, switch to the Network tab, reload the page, then export. In Chrome and Edge use the download icon, in Firefox use the gear menu and choose Save All As HAR, and in Safari use the Export button in the Network tab.

Can I see request and response bodies?

Yes, when the HAR was captured with content enabled. The inspector renders request payloads and JSON, HTML, or plain text response bodies, with pretty printing for JSON so you can read API responses without manual formatting.

Can I filter requests by type or status code?

Yes. Filter controls let you narrow the request list by HTTP method, status code range, resource type, or a URL substring. This turns a noisy capture of thousands of requests into just the ones that matter for your investigation.

Does it work with HAR files from any browser?

Yes. HAR is a standardized format, so the viewer accepts captures exported from Chrome, Edge, Brave, Firefox, and Safari. Any valid .har file with a log.entries array will load and render correctly in the inspector.

Can I analyze timing and TTFB information?

Yes. Each request shows its blocked, DNS, connect, TLS, send, wait (TTFB), and receive phases on a timing bar. This makes it easy to spot slow DNS resolution, long TLS handshakes, or high time to first byte during performance triage.

Why is a HAR file viewer useful for QA and support?

It lets you reproduce a user's exact network conditions from a single attached file, with no screen share or remote access. Support and QA teams use it to triage bug reports, slow page complaints, and API failures with concrete evidence.