HAR files, explained
HAR stands for HTTP Archive. It's the format browsers use to export a recording of network activity: every request, response, header, cookie and timing from a session, saved as a single JSON file. When a bug only reproduces on your machine, a HAR file is how you hand the evidence to someone else.
These guides cover the format end to end — capturing one properly, reading the structure, and the step everyone skips: stripping the secrets out before you share it.
How to open a .har file
There's no double-click experience: a .har file is plain JSON, so your operating system doesn't know what to do with it. A text editor will open it — and then choke, because real captures run to tens or hundreds of megabytes of unformatted JSON.
Chrome DevTools can import one: open the Network tab and drag the file into the request list to replay it as a read-only waterfall. Firefox's Network Monitor does the same trick. That gets you the raw tables — but no diagnostics, and no warning about the secrets sitting inside.
The fastest route is a dedicated viewer: drop the file into the .tools HAR viewer and you get the waterfall, per-request timings, automatic failure flags and a privacy scan — parsed entirely in your browser, nothing uploaded. Need a file to play with? Grab the sample HAR.