What this HAR file analyzer shows
A HAR file is the JSON log a browser exports from its Network panel. If you are new to the format, start with what a HAR file is. Once you load one, the analyzer gives you:
- A summary: request count, bytes transferred, the time span of the recording, failed requests, the slowest request and the number of pages.
- A request table with status, method, domain and path, type, size, time and a waterfall bar, sortable by time or size.
- Quick filters for failed requests, requests slower than one second and XHR/fetch calls, plus a text filter for a domain or path.
- A detail view per request with headers, query string, request body, the timing breakdown and a preview of text responses.
- A warning when the file holds Authorization, Cookie or Set-Cookie headers, token-like query parameters or JWTs.
How to analyze a HAR file
- Record the problem with the Network panel open and export the file. See how to create a HAR file in Chrome.
- Drop the file into the analyzer and read the sensitive data warning before anything else, so you know what not to paste into a ticket.
- Click Failed. In the default start-time order, the first failure is often the cause and later errors follow from it.
- Open the failing request and read the response body. APIs usually put the real error message there.
- Click Slow >1s, or sort by Time, and open the timings to see where each slow request spent its time.
- Sort by Size to find large images, scripts or JSON responses that delay the page.
Prefer DevTools? How to open a HAR file covers importing it into Chrome and querying it with jq.
A Google HAR Analyzer alternative that stays local
Google's HAR Analyzer in the Google Admin Toolbox is free and well suited to support cases. It groups requests by page, filters by status code class and can download a redacted copy of the file for sharing.
This analyzer runs entirely in your tab, which matters when the file holds a live session. It tells you up front which credentials the file contains, shows a per-phase timing bar for each request and pretty-prints JSON responses. It does not redact or re-export files, so use Google's tool or a sanitized export when you need a clean copy to send.
How to read HAR timings
Each entry has a timings object in milliseconds. A value of -1 means the phase did not apply, for example DNS on a reused connection.
blocked: time queued in the browser, often waiting for a free connection to the same host.dns: resolving the host name.connect: opening the TCP connection, including the TLS handshake.ssl: the TLS handshake on its own. It is already counted inside connect.send: sending the request headers and body.wait: waiting for the first byte of the response, also called TTFB. This is mostly server time.receive: downloading the response body.
The entry's total time is the sum of these phases without ssl. A long wait points to the server, a long blocked to the browser, and long dns or connect to the network.
What to look for in a HAR file
- Failed requests. A 401 or 403 points to auth, a 5xx to the server, and status 0 to a request that was blocked, cancelled or rejected by CORS.
- Slow TTFB. A large wait on an API call means the backend took that long to start answering.
- Large payloads. Sort by size: multi-megabyte images, scripts or JSON responses slow down the first render.
- Redirects. Several 301 or 302 responses in a row, often around login, add a round trip each.
- Repeated calls. The same endpoint called many times in a row usually means a retry loop or a component rendering too often.
Sensitive data in HAR files
A HAR file records whatever the browser sent and received, which can include session cookies, bearer tokens, API keys and personal data in responses. Anyone with the file can often replay the session. Recent Chrome versions export a sanitized HAR without Cookie, Set-Cookie and Authorization headers by default, but tokens in URLs and bodies stay in. Check the warning above before you share a file, and sign out of the recorded session afterwards to expire its cookies.
Frequently asked questions
- Is my HAR file uploaded anywhere?
- No. The analyzer reads the file with JavaScript in your tab and makes no network request with its contents. You can load the page, turn off your network connection and it still works. The site uses Google Analytics to count page visits, and that never receives the file.
- How do I analyze a HAR file?
- Drop it into the analyzer above. Check the Failed filter for 4xx, 5xx and status 0 responses, sort by Time to find slow requests and open the timings to see whether the wait (TTFB) or the download took longest, then sort by Size to find large payloads.
- What does status 0 mean in a HAR file?
- The request never got a response the browser could read. Common causes are a CORS rejection, an ad blocker or browser extension blocking the request, a request cancelled by navigation, or a network or DNS failure.
- What is a good TTFB in a HAR file?
- web.dev treats a time to first byte of 0.8 seconds or less as good for page loads. API calls are usually much faster, so a JSON request that waits more than a few hundred milliseconds is worth a look on the server side.
- Can it open large HAR files?
- Yes. Files of tens of megabytes parse in a few seconds. The table shows 200 rows at a time with a Show more button, and filters and sorting run over every request in the file. The practical limit is your browser's memory.
- Can Netraptor import HAR files?
- No. The Netraptor Chrome extension records API calls live in a DevTools panel and can export them as a sanitized HAR file. To open a HAR file someone sent you, use this analyzer or Chrome DevTools.