HAR file viewer

What a HAR is

A HAR (HTTP Archive) is what a browser exports from its network panel: a JSON log of every request a page made, with timings, sizes, status codes, headers and often the response bodies. It is the standard way to hand someone else a reproduction of a loading problem.

Why uploading one is a bad idea

A HAR captured from a signed-in session contains Cookie headers, Authorization headers, bearer tokens, CSRF tokens, form posts and API responses. It is one of the most sensitive files a developer routinely produces, and the common advice to upload it to a debugging site is genuinely dangerous.

This viewer reads the file in your browser. Nothing is transmitted, so the question does not arise.

The redacted copy

The most useful thing here is the sanitised download. Secret header values, cookies, tokens in query strings and post bodies are replaced, while header names stay — which header was present is usually the thing being debugged. That gives you a file you can attach to a bug report without handing over the session with it.

The tool also tells you how many secrets it found, and never displays them.

What it shows

• Total requests, transferred bytes and wall-clock time.
• A breakdown by type — document, script, stylesheet, image, font, XHR — and by host.
• The twenty slowest requests and the twenty largest.
• Failures, redirects, and any request made over plain http.
• How much came from third-party hosts.

How to capture one

Open developer tools, go to the Network tab, tick Preserve log, reload the page, then right-click the request list and choose Save all as HAR. Chrome, Firefox, Edge and Safari all produce the same format.

Limitations

Sizes recorded as -1 mean the browser did not measure them, and are counted as zero rather than subtracted. Response bodies are only present if the browser was asked to include them. A very large HAR is limited by memory.

Related tools

See the JSON formatter for reading the raw file.