Mightora · HAR troubleshooting guide
How to open and analyse a HAR file
Step-by-step HAR file analysis using Chrome, Edge or Firefox network tools and a private browser-side HAR analyser.
A HTTP Archive (HAR) is a JSON-formatted record of a browser's network requests. It includes URLs, HTTP response codes, timing measurements and often request or response content. HAR files are useful when a web application is slow, an API fails, or a page loads inconsistently.
1. Capture a HAR file in Developer Tools
- Open the affected page in Chrome or Microsoft Edge.
- Press F12 or open Developer Tools and select Network.
- Enable Preserve log when the problem involves navigation or a redirect.
- Reload the page or reproduce the failing action.
- Export or save the network log as a HAR file. The exact menu name varies between browser versions.
Firefox also provides a Network panel and HAR export. If the issue requires sign-in, remember that your HAR may contain credentials or authenticated URLs. Use the browser's options for sanitised exports when available, but still inspect the result before sharing.
2. Analyse locally, without uploading
Open Mightora HAR Analyser and choose your .har file. The tool parses entries in your browser. You can also use the downloadable offline HTML edition without an internet connection. Neither version submits HAR contents to an application server.
3. Find the requests worth investigating
- HTTP 4xx: look for authorisation errors, missing endpoints and validation failures.
- HTTP 5xx: investigate the relevant service and correlate its logs.
- Slow requests: look at total duration and the wait time before a response starts.
- Large responses: inspect payloads, caching and compression.
- Repeated requests: consider excess polling, retry loops or duplicate API calls.
4. Check timing context
HAR timing components describe individual requests, not necessarily full page load time. Requests overlap, so summing every duration overstates page latency. The P95 shown by the analyser is the 95th percentile of recorded request durations in that capture, not a production SLA measurement.
5. Share only a reviewed summary
You can export sanitised aggregate findings from the tool. This excludes raw request and response bodies, header values, cookies and query strings. However, hostnames and some URL path segments remain. Review any export before sending it to others.
Try it yourself: Open the free private HAR analyser or download the offline ZIP.
