HAR (HTTP Archive Format)

The HTTP Archive (HAR) format is a standardized, JSON-based specification for recording detailed web browser network transaction logs. Maintained under the W3C Web Performance Working Group draft, a .har file captures the complete lifecycle of every HTTP and HTTPS transaction made during a browsing session—including requested URLs, redirect chains, HTTP headers, request and response cookies, payloads, and millisecond-accurate waterfall timing phases (DNS lookup, TCP connect, SSL handshake, TTFB, and download duration).

Analyze network waterfalls and detect performance bottlenecks with our privacy-friendly HAR Analyzer or export requests with HAR to Postman Converter.

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Technical Specifications at a Glance

Specification	Details
Standard Reference	W3C Web Performance Working Group Draft / Jan Odvarko (Firebug)
Data Format	Strict UTF-8 JSON
Standard File Extension	.har
MIME Media Type	application/json
Exporting Tools	Google Chrome, Safari, Firefox, Edge, Charles Proxy, Fiddler, Playwright
Waterfall Metrics	Blocked, DNS, Connect, SSL, Send, Wait (TTFB), Receive

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Anatomy of a HAR File Document

A .har file contains a top-level log object holding browser metadata, page references, and an array of entries:

{
  "log": {
    "version": "1.2",
    "creator": {
      "name": "DevFlow Network Recorder",
      "version": "1.0"
    },
    "pages": [
      {
        "startedDateTime": "2026-09-04T12:00:00.000Z",
        "id": "page_1",
        "title": "DevFlow Tools Hub",
        "pageTimings": {
          "onContentLoad": 412,
          "onLoad": 820
        }
      }
    ],
    "entries": [
      {
        "pageref": "page_1",
        "startedDateTime": "2026-09-04T12:00:00.120Z",
        "time": 75.4,
        "request": {
          "method": "GET",
          "url": "https://devflow.tools/api/tools",
          "httpVersion": "HTTP/2.0",
          "headers": [
            { "name": "accept", "value": "application/json" }
          ]
        },
        "response": {
          "status": 200,
          "statusText": "OK",
          "content": {
            "size": 18450,
            "mimeType": "application/json; charset=utf-8"
          }
        },
        "timings": {
          "blocked": 1.2,
          "dns": 14.5,
          "connect": 18.2,
          "ssl": 15.0,
          "send": 0.5,
          "wait": 21.0,
          "receive": 5.0
        }
      }
    ]
  }
}

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Deconstructing the 7 Waterfall Timing Phases

When diagnosing web latency, each HAR entry breaks transaction duration into discrete phases:

[ Blocked ] ──> [ DNS ] ──> [ Connect ] ──> [ SSL ] ──> [ Send ] ──> [ Wait (TTFB) ] ──> [ Receive ]

1. Blocked: Time waiting in the browser queue for an available network socket connection.
2. DNS: Time required to resolve the hostname via DNS.
3. Connect: Time spent establishing the TCP three-way handshake.
4. SSL / TLS: Time negotiating the cryptographic cipher suite and exchanging TLS certificates.
5. Send: Time spent uploading the HTTP request headers and payload to the wire.
6. Wait (TTFB - Time to First Byte): Time waiting for the server to process the request and return the very first byte of response data.
7. Receive: Time required to stream and download the remaining response body bytes.

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Security Warning: Sanitizing Secrets in HAR Files

Because HAR files capture the raw network traffic verbatim, exporting a HAR from your browser often captures highly sensitive credentials, including:

• Authorization: Bearer <token> headers
• Session cookies (Set-Cookie: session_id=...)
• Credit card numbers or passwords submitted in form POST payloads
• API keys embedded in query strings

[!CAUTION] Never upload an unredacted HAR file to public forums or third-party ticketing systems without sanitizing authentication tokens first.

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Frequently Asked Questions

How do I export a HAR file from Google Chrome or Microsoft Edge?

1. Press F12 or Ctrl + Shift + I (macOS: Cmd + Option + I) to open DevTools.
2. Switch to the Network tab.
3. Reload the page to capture network requests.
4. Click the Export HAR icon (downward arrow) in the top-right toolbar to save the .har file locally.

Can I convert recorded browser sessions into API collections?

Yes! Instead of manually typing endpoints into Postman or Insomnia, upload your exported .har recording into our HAR to Postman Converter to automatically generate structured API collections with headers and sample bodies.

What causes high "Wait" (TTFB) times in a HAR file?

A disproportionately long Wait phase indicates backend server latency—such as unoptimized database queries, slow external API calls, or CPU-bound server rendering—rather than network bandwidth or CDN delivery issues.