HAR analyzer & HAR file viewer
Drop in a HAR file from your browser's Network panel and this free HAR analyzer shows the waterfall, where the time to first byte went, the slowest and largest requests, and what to fix: errors, redirects, missing compression, short cache lifetimes and third parties. The file is read in your browser and never uploaded.
Drop a .har file here
It is read in your browser and never uploaded, because a HAR file can hold cookies, login headers and tokens.
One recording is one sample. Synthetic Monitoring keeps recording.
It tests your pages with Lighthouse on a schedule, keeps every waterfall and alerts you when a metric crosses your line. Ask Theo, the AI assistant in the app, to explain any finding.
What it checks
- Splits the time to first byte of the page into redirects, DNS lookup, connection, TLS and server wait, and grades it on Google's 800 ms and 1.8 s lines
- Lists 4xx and 5xx errors, failed requests, redirect chains and plain HTTP requests on an HTTPS page
- Flags text files sent without compression, static files with no or a short cache lifetime, and files downloaded twice
- Breaks the load down by type, domain, protocol and request phase, with a filterable waterfall and a CSV export
What it does not
- It reads one load, recorded on one machine and network. Run it a few times before you trust a number
- It sees only what the browser wrote into the file. Firefox and Safari leave out details Chrome records, such as priority and what started each request
- A HAR has no paint timings, so first paint and LCP are not here. Render-blocking files are flagged only where the HAR gives evidence
- It does not look inside responses, so it cannot say why a script is slow or what it does
Questions
How do I export a HAR file?
In Chrome or Edge: open DevTools, go to the Network tab, check Preserve log, reload the page, then use the download arrow (Export HAR).
In Firefox: Network tab, reload, then right-click any request and choose Save All As HAR.
In Safari: enable the Develop menu, open Web Inspector, go to Network, reload, then click Export.
Is it safe to upload a HAR file?
Often not. A HAR records request and response headers, so it can hold your cookies, login tokens and API keys. Anyone with the file can reuse a live session. This analyzer never uploads it: your browser reads the file and builds the report on your computer. If you share a HAR with anyone else, remove the cookies and Authorization headers first, or record it in a private window you then log out of.
What is a good time to first byte?
Google calls up to 800 ms good and over 1.8 s poor, measured from the start of the navigation, redirects included. In a HAR, look at the page's first request: DNS, connection and TLS are the network, and server wait is your server building the page.
Why are some sizes and timings missing?
A HAR marks anything the browser did not measure with -1, and I show it as unknown rather than zero. Files served from the browser's cache have no network timings. A request on a connection the browser already had open has no DNS lookup or handshake to time.
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