What is a HAR file?
A HAR (HTTP Archive) file is a JSON document that records network activity captured by a browser or another HTTP debugging tool. Each entry normally describes one request and its response, including the URL, HTTP method, status code, headers, content metadata and timing information.
How to open a HAR file
- Open the HAR Analyzer.
- Drag the .har file into the upload area or choose it from your device.
- Start with the overview to check request count, transfer size, domains, failures and redirects.
- Use the Requests table to search and filter individual network calls.
- Open the Waterfall and Performance tabs to investigate slow resources.
How to read the Requests table
Status
2xx responses normally indicate success, 3xx indicates redirects, 4xx indicates client-side request problems such as 404 Not Found, and 5xx indicates server-side failures.
Method
GET requests usually retrieve data. POST, PUT and PATCH often send or change data, while DELETE commonly removes a resource. The exact behavior depends on the application.
Size and type
Large JavaScript bundles, images, fonts or media can contribute significantly to transfer size. MIME type helps identify what kind of resource was returned.
Understanding HAR timings
HAR timing fields can include blocked, DNS, connect, SSL, send, wait and receive. A high wait value often contributes to a high TTFB, while a high receive duration may point to a large response or slow transfer.
How to use a waterfall
A waterfall visualizes request start times and durations relative to one another. Look for long bars, chains of redirects, groups of blocking requests and late-loading critical assets. The waterfall is most useful when considered together with status codes, resource size and individual timing phases.
How to find common problems
- 404 / 410: missing or removed resources.
- 500 / 502 / 503: server or upstream failures.
- Redirect chains: repeated 3xx responses before the final resource.
- High TTFB: long server wait time or network latency.
- Heavy third-party traffic: analytics, ads, widgets or external scripts making many requests.
- Large resources: oversized images, scripts, fonts or API payloads.
HAR files and privacy
Before sharing a HAR file, remember that it can contain cookies, authentication tokens, private parameters and request/response bodies. Use the HAR Sanitizer and manually review the result before sharing.