Why it matters
A HAR file is a complete recording of a page load: every request, header, timing and size. It's the best thing to send a developer when a page is slow, but it's a large JSON file that's hard to read, and it contains your cookies and login tokens. Online viewers often ask you to upload it, which means handing those over.
This analyser reads the file in your browser. It draws the waterfall from each request's own timing phases, so you can see whether time goes on connecting, waiting for the server or downloading, and marks DOMContentLoaded and load. It totals weight by type and domain, splits first and third parties, and checks every response for the usual problems: text sent without compression, static files without a long cache lifetime, heavy images, redirects, slow first bytes, duplicate downloads, errors and cookies sent with every image. Each finding says what to change. When you need to share the file, download a redacted copy first.
How it works
- InputA HAR file from DevTools
- In your browserTimings, weight and response headers read on your device
- OutputA waterfall, fix list and a redacted copy
Where it fits in a designer's workflow
- Plan
- Design
- Build
- Test
- Launch
By the numbers
Show the numbers as a table
| Type | Requests | Transferred |
|---|---|---|
| Images | 7 | 1114.1 KB |
| JavaScript | 4 | 258.9 KB |
| CSS | 3 | 134.1 KB |
| Fonts | 2 | 66.9 KB |
| HTML | 2 | 18.6 KB |
| API | 3 | 5.7 KB |
| Other | 1 | 300 bytes |
How to use it
- In Chrome or Edge, open DevTools, go to Network, reload the page, then use Export HAR. Firefox and Safari have the same option.
- Drop the file here or paste its contents.
- Read the summary and the fix list, then look at the waterfall for long bars.
- Before sending the file to anyone, download the redacted copy.
FAQ
What is a HAR file?
HTTP Archive: a JSON record of every request a page made while DevTools was recording, with headers, timings, sizes and sometimes response bodies. Browsers and proxy tools export it.
Is it safe to share a HAR file?
Not as it is. It contains cookies, Authorization headers and often tokens in URLs, which can let someone sign in as you. Use the redacted download here, which removes those, plus request and response bodies.
Why does a request show no timing phases?
Some tools only record the total time, and requests served from memory or a service worker have no network phases. Those are drawn as a single bar.
How is first or third party decided?
From the main page's site: anything on the same registrable domain (including subdomains, and co.uk-style suffixes) is first party; everything else is third party.
Are the savings exact?
No. Compression savings use typical gzip ratios for each type and image savings assume a modern format at the displayed size. They show what's worth fixing first.
