View HAR captures privately
A HAR file (HTTP Archive) is a JSON record of the network requests your browser made, exported from the DevTools Network tab. This viewer opens it locally and lays every request out in a table — method, status, type, size and timing — so you can spot slow calls, failed responses and oversized assets without sharing the file with anyone.
How it works
When you select a .har file, the tool reads it with the browser’s FileReader
API and parses the JSON. It walks log.entries and, for each request, pulls out
the method and URL from request, the status, status text, MIME type and content
size from response, and the total round-trip time. Sizes are formatted into
B, KB or MB, and a content size of -1 (body not captured) is shown as a dash
and left out of the total. You can filter the table by URL substring; the request
count and summed byte total recalculate to match what is shown. Status codes of
400 or higher are flagged in red.
Example
Open a HAR captured from a slow page and you might see:
| Method | Status | Type | Size | Time | URL |
|---|---|---|---|---|---|
| GET | 200 | text/html | 14.2 KB | 320 ms | /index.html |
| GET | 200 | application/javascript | 512.0 KB | 1100 ms | /app.bundle.js |
| GET | 404 | text/html | - | 88 ms | /missing.png |
The 512 KB JavaScript bundle taking 1100 ms is the obvious bottleneck, and the 404 highlights a broken asset reference.
What to look for in a HAR file
High total time on a single request: Sort by the Time column descending to find the single slowest request. This is usually either a large asset or a slow API call. A slow API call on the critical rendering path is the most common cause of a poor page load experience.
Many requests to the same domain: Count the requests to your own domain. A page making 60–100 requests has a waterfall problem — too many small files. Modern HTTP/2 makes this less bad than it was, but bundling and caching strategy are worth reviewing.
Large assets without compression: JavaScript or JSON responses over 100 KB should almost always be gzip or brotli compressed. If the content-type is application/javascript and the size is large, check whether the response headers show Content-Encoding: gzip.
4xx and 5xx status codes (highlighted in red): Filter for error codes to identify broken asset references, failed API calls, and authentication failures. A single 401 on an API call can silently break a whole section of functionality without a visible page error.
Request bodies you did not expect: HAR files exported with content include full request and response bodies. You may find API keys, session tokens, or personal data in them — this is why you should review a HAR file before sharing it with a support team.
How to export a HAR file
In Chrome or Edge: Open DevTools (F12), go to Network tab, reproduce the activity, then click the download icon or right-click any request and choose “Save all as HAR with content”.
In Firefox: Open DevTools (F12), go to Network tab, click the gear icon, choose “Save All As HAR”.
In Safari: Enable the Develop menu in Preferences, open Web Inspector, go to Network, then Export.
Because HAR files frequently include cookies, authorization headers and full request bodies, privacy matters: this tool parses the file entirely in your browser and never uploads it.