HAR File Analyzer

Visualize browser network waterfalls from .har files. See request timings, status codes, slowest calls, largest responses. Runs entirely in your browser — nothing uploaded.

1.0.0
Version
Auth
Batch

About HAR File Analyzer

A teammate sends you a network.har file as evidence that the checkout page is slow on their machine. Your options for actually reading it are limited: paste it into Google's HAR Analyzer (upload- based, hosted), re-import it into your own DevTools (which messes up your local Network tab state), or open it in a text editor and scroll through 200 KB of JSON looking for the slow request. None of these are great when the file might contain auth tokens, internal API hostnames, or anything else you wouldn't paste into a public web service.

This HAR file analyzer drops the JSON onto the page and renders the things you actually need in five seconds: a waterfall timeline showing per-request DNS / Connect / Wait / Receive phases, the top slowest requests sorted by total time, the largest responses by bytes, a status-code breakdown (2xx/3xx/4xx/5xx), a resource type split (XHR/JS/CSS/Image/Font/Document/Other) and a domain breakdown so you can see which third party is dragging the page down. The request list is filterable by URL substring, status code or type, and clicking any row expands to the full headers, cookies, query string and post body. Everything runs as JavaScript in the page — the HAR never uploads, and its embedded auth tokens stay on your machine.

Use it to triage a slow-page report from a colleague, debug a third-party script that's blocking page load, find the one image that weighs 5 MB, audit how many CDN domains a checkout flow touches, hand a customer-support engineer a sanitised summary instead of the raw file, or hunt down a 5xx in a HAR from a flaky CI run. Tested with Chrome, Firefox, Edge and Safari DevTools exports.

HAR File Analyzer Use Cases

  • Front-end engineers triaging a slow-page HAR from a teammate or customer
  • Debugging a third-party script that's blocking page load or LCP
  • Finding the one oversized image or font slowing a checkout flow
  • Auditing how many CDN and tracker domains a page actually touches
  • Sanitising a HAR before sharing it — read auth tokens before forwarding
  • Post-incident analysis of HARs collected during a production slowdown
  • QA engineers comparing waterfalls across browsers (Chrome vs Firefox)

HAR File Analyzer Features

  • Waterfall timeline with per-request phases — Blocked, DNS, Connect, SSL, Send, Wait (TTFB), Receive
  • Top-N slowest requests and largest responses tables for finding the worst offenders fast
  • Status-code breakdown split into 2xx/3xx/4xx/5xx with click-to-filter on each bucket
  • Resource-type breakdown — XHR, JS, CSS, Image, Font, Document, Other — to see where bytes go
  • Per-domain rollup showing total requests, total bytes and total time per host so third-party load is obvious
  • Filterable request list — by URL substring, by status code, by resource type — with click-to-expand for full headers/cookies
  • All parsing and rendering runs as JavaScript in your browser — HAR contents, including embedded auth tokens, never upload

How to Use HAR File Analyzer

Export a HAR from DevTools

In Chrome or Firefox: open DevTools (F12), go to the Network tab, reproduce the slow page or request, right-click anywhere in the request list and choose 'Save all as HAR with content'. Edge and Safari work the same way with slightly different menu wording.

Drop the .har on the page

Drag-and-drop the saved .har file onto the upload zone, or click to browse. The parser handles HAR 1.1 and 1.2 spec files from Chrome, Firefox, Edge, Safari, Charles Proxy and Fiddler exports.

Scan the summary cards

The top cards show total requests, total bytes, total wall time and a status-code split. The Top Slowest and Largest Responses panels surface the worst offenders without you having to scroll the request list.

Read the waterfall

Below the cards, every request renders as a horizontal bar coloured by phase — Blocked (grey), DNS (cyan), Connect (green), SSL (orange), Wait or TTFB (purple), Receive (blue). Long Wait bars usually mean a slow backend; long Receive bars mean payload size or slow downlink.

Filter and drill into a request

Use the filter bar to narrow by URL, status code or resource type. Click any row to expand request and response headers, cookies, query parameters and post body for that specific call.

HAR File Analyzer FAQ

No. The file is read with FileReader, parsed as JSON, and rendered entirely as JavaScript on the page. There is no fetch, no XHR, no analytics call referencing your file's contents. This matters because HAR exports routinely include Cookie and Authorization headers, request bodies with credentials, and internal API URLs you would not want sitting on a third-party SaaS — they stay on your machine here.

Chrome, Firefox, Edge and Safari DevTools 'Save all as HAR with content' files, plus Charles Proxy, Fiddler and BrowserStack HAR exports. The parser follows the HAR 1.2 specification (the same as the W3C draft) and is backwards-compatible with the older 1.1 layout. Vendor extensions are ignored, so an export from a less common tool will still parse if it follows the core schema.

There's no hard server limit (parsing is local), but in practice browser performance starts to suffer above 50 MB or 5,000 requests. For very large HARs (CI artefacts, long sessions) consider opening just the slice you care about — DevTools lets you clear the network log and re-record only the relevant interaction.

Google's HAR Analyzer is upload-based — your file goes to Google's servers for parsing. This tool runs in your browser so the HAR (and the auth tokens or internal URLs inside it) stays on your machine. It also surfaces the request waterfall by default rather than only summary tables, which is usually the first thing you want when triaging a slow page.

Each request bar is split into phases per the HAR spec: Blocked (waiting in browser queue, grey), DNS lookup (cyan), Connect — TCP handshake (green), SSL handshake (orange), Send (the request bytes leaving), Wait — TTFB, time-to-first-byte from the server (purple), Receive (downloading the response body, blue). Long Wait = slow backend; long Receive = big payload or slow link; long Blocked = browser-side queue pressure (too many concurrent requests to one origin).

This viewer is read-only and does not rewrite the file. For sanitising, the standard approach is to load the file, identify the rows with sensitive auth headers or PII in the response body, then run a script (jq, or har-sanitizer on npm) that strips those headers from the raw JSON. You can re-load the sanitised file here to confirm the offending values are gone before forwarding.

HAR exports record the timing each browser saw — Chrome, Firefox and Edge measure phases slightly differently, and service workers, HTTP/2 push and connection coalescing can compress what looks like a long bar in the live DevTools into a short bar here, or vice versa. The values are accurate; the rendering of overlapping requests can just look different from the live tab. The Wait (TTFB) and total time numbers are the most reliable indicators of backend slowness.

Zero uploads. HAR files are parsed entirely in your browser — nothing is sent to a server.

Upload a .har file

Exported from Chrome/Firefox DevTools Network tab

HAR File Analyzer Tutorial

What is a HAR file?

HAR (HTTP Archive) is the JSON format browsers use to export a page's complete network activity. It captures every request the page made: timing breakdown (DNS, connect, wait, download), status codes, payload sizes, headers. DevTools gives you one-click export.

How to Export a HAR File

  • Chrome/Edge: Open DevTools → Network tab → reload the page → right-click any request → "Save all as HAR with content"
  • Firefox: Dev Tools → Network → gear icon → "Save All As HAR"
  • Safari: Develop menu → Web Inspector → Network → Export

What You'll See

  • Stats cards — totals, status code distribution, total transfer size
  • Waterfall timeline — every request plotted against page time, with color-coded phases (DNS, connect, wait, receive)
  • Slowest requests — top 10 by time
  • Largest responses — top 10 by bytes
  • Resource type breakdown — scripts vs images vs XHR
  • Domain breakdown — how many requests went to each host
  • Filterable request table — search by URL or status

Why In-Browser?

HAR files often contain auth tokens, cookies, and API payloads — in short, secrets. Uploading one to a random server is dangerous. This tool runs entirely as JavaScript in your browser; your HAR never leaves the page.