What is a HAR File?
A HAR (HTTP Archive) file is a standardized JSON-formatted archive that records all network interactions between a web browser and a server. Modern browsers like Chrome, Edge, and Firefox, as well as debugging proxies like Charles or Fiddler, can export their Network panel directly into a .har file.
Why Analyze HAR Files Client-Side?
HAR files capture complete raw HTTP transactions, which often include session cookies, authorization tokens, API keys, and personal payloads. Uploading a HAR file to third-party web servers introduces major credential exposure risks. Lucentool parses everything entirely inside your browser memory with zero network uploads.
Waterfall Timing Breakdown
- DNS Lookup: Time spent resolving DNS. High values indicate a need for DNS prefetching or faster nameservers.
- Initial Connection & SSL: TCP handshake and TLS negotiation. Can be reduced to near-zero with connection reuse (HTTP/2 or HTTP/3).
- TTFB (Wait): Time To First Byte. Measures backend computation, database query duration, and gateway routing latency.
- Content Download: Time taken to transfer the response payload. High download times indicate lack of Gzip/Brotli compression or asset bloat.