Failed requests with HAR Desk
This opens a made-up capture with a 502 on the payment call, a missing script, a request blocked by a browser extension and a 500. The failed filter is already on, so the problem rows are the first thing you see.
- Load the HAR and look at the Failures box: it counts status 0, 4xx and 5xx.
- Click a failing request to read its response headers and body for the error message.
- Check the Timing tab: a 502 after 30 seconds is a timeout upstream, a 0 with an error text is a blocked or cancelled call.
- Download the support pack to hand the failing requests, slowest calls and timings to someone else.
What to know
A request counts as failed here when its status is 0 (nothing came back: blocked by an extension, cancelled, DNS or TLS failure, CORS), 4xx or 5xx, or when the browser recorded an error text. Redirects (3xx) are not failures. Status 0 is the one people miss, because there is no response to read; the error text on the entry, such as net::ERR_BLOCKED_BY_CLIENT, is the clue.
Read a failure in three steps: the status and where it happened in the waterfall, then the response body if the capture kept it, then the request itself (method, query and body). A 502 or 504 that took 30 seconds points at a proxy waiting on a slow upstream. A 404 on a script right after a deploy usually means the page references a hashed file that no longer exists.
Bodies are only shown when the recording kept them. If the response body is missing, record again with the option to save content turned on. The failing-requests table in the support pack lists up to 40 rows with method, status, time and URL, which is usually enough for a ticket.
Updated · Cosmovex
Questions
What does status 0 mean in a HAR?
The browser got no HTTP response: the request was blocked, cancelled, failed at DNS or TLS, or stopped by CORS or an extension. The entry often has an error text such as net::ERR_BLOCKED_BY_CLIENT.
Are redirects counted as failures?
No. 3xx responses are shown with their own count but are not in the failed list.
Why is the response body empty for a 500?
The capture may not have saved response content. Record again with content saving on, or check the response headers and timing for clues.
Can I filter failures by host or type?
Yes. Combine the failed filter with the text, method, type and third-party filters.
The free plan covers everything on this page. HAR Desk Pro ($29, paid once) is described on the HAR Desk page.
