Frequently Asked Questions
What is a HAR file?
A HAR (HTTP Archive) file is a JSON-formatted log of all network requests made by a browser during a recording session. It captures request and response headers, bodies, timing data, cookies, and more. It is the standard format used by Chrome DevTools, Firefox, Safari, and other browsers for exporting network activity.
How do I export a HAR file from Chrome?
Open Chrome DevTools (F12), go to the Network tab, reproduce the activity you want to capture, then right-click any request and choose 'Save all as HAR with content', or click the download icon in the toolbar.
How do I export a HAR file from Firefox?
Open Firefox DevTools (F12), go to the Network tab, reproduce the activity, then click the gear icon and choose 'Save All as HAR'. Alternatively, right-click a request and select 'Save all as HAR'.
Is my HAR data safe? Does it get uploaded?
No data is ever uploaded. All HAR file processing happens entirely in your browser using JavaScript. The file never leaves your device. This is important because HAR files can contain sensitive data like cookies, authorization headers, and response bodies.
What can I debug with a HAR file analyzer?
You can debug slow page loads by inspecting timing waterfall charts, find failed requests (4xx/5xx errors), check CORS and security headers, inspect API request and response bodies, analyze cookie behaviour, identify large resources causing performance issues, and measure Time to First Byte (TTFB) across requests.
What is TTFB and why does it matter?
TTFB (Time to First Byte) is the time from when a request is sent until the first byte of the response is received. It includes DNS lookup, TCP connection, SSL handshake, and server processing time. A high TTFB indicates slow server response or network latency and is a key metric for web performance.
What does the waterfall chart show?
The waterfall chart shows when each request started relative to the page load timeline, and how long each timing phase took. Phases include: Blocked, DNS lookup, TCP connect, SSL/TLS handshake, Request send, Wait (TTFB), and Content download. Each phase is color-coded for easy identification.
Can I filter requests in the HAR analyzer?
Yes. You can filter by resource type (XHR, JS, CSS, images, fonts, media), HTTP status code (2xx, 3xx, 4xx, 5xx), HTTP method (GET, POST, PUT, DELETE, PATCH), domain, minimum response time, and by searching the URL. Filters can be combined.
What is the difference between transferred size and content size?
Transferred size is the actual number of bytes sent over the network, which is smaller when compression (gzip or brotli) is applied. Content size is the uncompressed size of the response body. The difference shows how much compression saves in bandwidth.
Can I export the analyzed data?
Yes. You can export the currently filtered requests as a CSV file containing request number, method, URL, status, resource type, size, total time, domain, and TTFB. You can also copy any individual request as a cURL command from the Overview tab in the detail panel.