HAR File Analyzer
Analyze HTTP Archive (HAR) files online to inspect network requests, response times, status codes, payload sizes, redirects, headers, and performance waterfalls directly in your browser.
| # | Status | Method | Request URL | Duration | Transfer | Type | Action |
|---|---|---|---|---|---|---|---|
| 1 | 200 | GET | app.toolmono.internal/ | 145 ms | 6.9 KB | Document | |
| 2 | 200 | GET | api.toolmono.internal/v1/auth/session | 95 ms | 0.8 KB | API | |
| 3 | 200 | GET | api.toolmono.internal/v1/tools?limit=50 | 180 ms | 14.0 KB | API | |
| 4 | 304 | GET | cdn.toolmono.internal/static/logo.svg | 65 ms | 0.1 KB | API |
How to Use
1. What is a HAR (HTTP Archive) File and How Does it Work?
An HTTP Archive (HAR) file is a standardized JSON-formatted file used by web browsers and automated test suites to record all network activity during a web session.
Standardized by the W3C Web Performance Working Group, HAR files capture comprehensive request metadata including request and response headers, query parameters, cookies, payloads, HTTP status codes, and granular timing breakdowns (DNS lookup, SSL handshake, Time to First Byte, and content download).
2. How to Export HAR Files in Chrome, Edge, and Firefox
- Press F12 or Ctrl+Shift+I.
- Switch to the Network tab.
- Reproduce the issue or reload.
- Right-click any request row.
- Click Save all as HAR with content.
- Press F12 to open DevTools.
- Navigate to the Network tab.
- Record network requests.
- Click the Export HAR icon (downward arrow).
- Save the
.harfile to disk.
- Open Web Developer Tools (F12).
- Click the Network monitor tab.
- Trigger your network operations.
- Click the gear icon in the top right.
- Select Save All As HAR.
3. How to Analyze Network Traffic and Performance Online
Follow these steps to analyze a HAR file with ToolMono:
- Upload or Paste: Drop your
.harfile into the dropzone or switch to Paste HAR JSON mode. - Review Health Score: Check the Network Health Score (0–100) and high-level KPIs (Total Requests, Failed 4xx/5xx, Slow, and Redirects).
- Filter & Search: Use quick filter chips (2xx, 3xx, 4xx, 5xx, Slow, Large, API) or full-text URL search to isolate target endpoints.
- Inspect Waterfall: Switch to the Timing Waterfall tab to visualize request overlap and latency bottlenecks.
- Open Deep Inspector: Click any request row to review headers, cookies, timing phases, query parameters, and payloads.
- Export Reports: Download formatted Markdown summaries or structured JSON reports for pull requests and CI/CD logs.
4. Network Health Score (0–100) & Core Performance Metrics
The Network Health Score provides an explainable 0–100 index of network quality based on deterministic criteria:
- 5xx Server Errors: -10 points each (critical backend failure)
- 4xx Client Errors: -4 points each (broken links or unauthorized requests)
- Slow Requests (>1000ms): -2 points each (latency degradation)
- Duplicate Request Groups (≥3 calls): -2 points each (wasted bandwidth)
5. Request Categorization: APIs, Documents, Scripts & Assets
6. Understanding Timing Phases: DNS, SSL, TTFB & Waterfall
HAR files break request duration down into distinct phases:
- Blocked / Queueing: Time spent waiting in browser network queue.
- DNS Lookup: Time required to resolve domain name to IP address.
- Connect & SSL: TCP three-way handshake and TLS negotiation.
- Wait (TTFB): Time to First Byte spent waiting for server processing.
- Receive: Time spent downloading the response content body over the network.
7. Detecting Slow Requests & High Latency Endpoints
Requests with excessive latency delay user interactions. ToolMono allows you to adjust the slow threshold (250ms, 500ms, 1000ms, 2000ms) and immediately filters requests exceeding this limit.
8. Investigating 4xx Client and 5xx Server Errors
Failed network requests are isolated into 4xx Client Errors (such as 401 Unauthorized, 403 Forbidden, 404 Not Found) and 5xx Server Errors (500 Internal Server Error, 502 Bad Gateway, 504 Gateway Timeout), enabling root-cause diagnosis.
9. Duplicate Request Detection & Bandwidth Waste
Redundant queries occur when client components request the exact same URL multiple times during initial page load. The analyzer groups duplicate queries and calculates total wasted network bandwidth.
10. Multi-Hop Redirect Chain Analysis (301, 302, 307)
Chained redirects (e.g. https://legacy.domain.com → https://domain.com → https://www.domain.com/en) add unnecessary round-trip latency. The analyzer traces full redirect hops.
11. Cache-Control, ETag & 304 Not Modified Diagnostics
Evaluates HTTP caching headers (Cache-Control, ETag, Last-Modified, Age) and highlights 304 Not Modified conditional cache hits.
13. CORS Headers, Security Policies & Information Disclosure
Identifies CORS response headers (Access-Control-Allow-Origin, Access-Control-Allow-Credentials), security headers (CSP, HSTS), and server version disclosures (Server, X-Powered-By).
14. Safe Non-Executable JSON & HTML Payload Inspector
All response bodies (JSON, HTML, JavaScript) are strictly displayed as syntax-highlighted static text inside isolated containers. No active scripts or external assets are ever executed from uploaded HAR archives.
15. 100% In-Browser Privacy & HAR Sanitizer Integration
When you load a HAR file into ToolMono, 100% of the JSON parsing and performance calculations occur directly within your web browser. Nothing is uploaded to any server. Before sharing a HAR file with external vendors, use our HAR Sanitizer to redact private session tokens.
16. Step-by-Step Practical HAR Debugging Walkthrough
Sample network analysis output for an e-commerce checkout session:
HAR Summary: 12 Requests (Total: 4.2 MB) Health Score: 78 / 100 (Needs Attention) Findings: 1. [ERROR] 1 Server Error: POST /v1/payments/process (HTTP 500) 2. [WARNING] 1 Slow Request: GET /v1/analytics/reports (2850ms TTFB) 3. [WARNING] 1 Large Response: GET /images/hero-banner.png (2.85 MB) 4. [INFO] 1 Redirect Chain: https://example.com/v1 -> https://www.example.com/en
17. Authoritative References & Standards
Consult official web performance specifications and developer documentation:
W3C Web Performance Working Group: HAR 1.2 Specification
Official specification for HTTP Archive format structure, timing phases, and entry objects.
MDN Web Docs: HTTP Archive (HAR) format
Comprehensive documentation of HAR files, browser exports, and network recording.
Chrome DevTools: Inspect Network Activity
Official Google Chrome documentation for analyzing waterfalls, TTFB, and network payloads.
Firefox Developer Tools: Network Monitor
Official Mozilla Firefox guide for inspecting HTTP transactions and timings.
18. Frequently Asked Questions (20 FAQs)
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