Critical Request Chain Viewer: Free Online HAR Critical Request Chain Analyzer — How-To Guide

Slow page loads are often caused by a chain of blocking requests: a script that loads another script, which loads a font, which triggers more downloads. The Critical Request Chain Viewer builds a best-effort critical request chain summary from HAR entries and initiators, so you can see which requests actually stand in the way of rendering.

Try it free: Critical Request Chain Viewer

What the Tool Does

The Critical Request Chain Viewer takes the raw network data your browser captures — HAR (HTTP Archive) entries — and turns it into a readable summary of the critical request chain. Instead of scrolling through hundreds of rows in a HAR file, you get a focused view of which requests were initiated by which, and which ones form the chain that delays your page.

It is built as a first-pass local tool: paste real input, run the parser, review clear findings, then copy or download the output. There is no account to create and no server-side processing.

Step-by-Step: How to Use It

1. Export a HAR file from your browser. In Chrome or Edge, open DevTools (F12), go to the Network tab, reload the page, then right-click the request list and choose Save all as HAR with content. Firefox has the same option under its Network Monitor.
2. Open the viewer. Go to Critical Request Chain Viewer. If you want to explore first, the page offers sample input so you can see the output format without hunting down a HAR file.
3. Paste your HAR entries. Drop the HAR JSON into the input area. The tool runs validation so malformed input is flagged before you waste time on bad results.
4. Run the parser. The tool builds the critical request chain summary from the HAR entries and initiators, showing the sequence of dependent requests that matter most for load time.
5. Review the findings. Read the chain from top to bottom: early entries are the requests that block everything downstream. This is where you spot the long font chain, the unbundled third-party script, or the redirect adding a full round trip.
6. Copy or download your report. Copy the output for a code review comment or download a text report to attach to a QA handoff or debugging notes.

3 Practical Tips

• Capture a cold load. Clear your cache before exporting the HAR (DevTools → disable cache with DevTools open) so the chain reflects what a first-time visitor experiences, not a cached repeat view.
• Use the summary in code review prep. A chain summary is much easier for a reviewer to scan than a full HAR file. Paste the relevant chain segment into your PR description when your change touches asset loading.
• Treat it as a first pass, not a final verdict. The tool is designed for fast local inspection. For regulated production changes, verify final results with your project's own compiler, CI checks, or infrastructure scanner.

FAQ

Does the Critical Request Chain Viewer upload my input?
No. The normal workflow runs locally in your browser — your HAR data never leaves your device.

Is this a full replacement for CI or production scanners?
No. It is designed for fast local inspection before you run project-specific checks, which is exactly where most load-time debugging starts.

Can I copy or download the result?
Yes. Run the tool, then copy the output or download a text report for documentation, QA handoffs, or debugging notes.

Do I need an account or to install anything?
Neither. The page works in your browser with no sign-up and no installation.

Privacy Note

Your HAR files can contain sensitive details — URLs, headers, sometimes tokens. That's why this matters: the Critical Request Chain Viewer runs 100% in the browser. Your files never leave your device, so you can analyze real production captures without sending them anywhere.

Try it free: Critical Request Chain Viewer