HAR files

mitm2openapi reads HAR (HTTP Archive) files — the standard format for exporting browser network traffic. HAR version 1.2 is supported.

Producing HAR files

Browser DevTools

All modern browsers export HAR from their Network tab:

• Chrome/Chromium: DevTools → Network → right-click → "Save all as HAR with content"
• Firefox: DevTools → Network → gear icon → "Save All As HAR"
• Safari: Web Inspector → Network → Export button

HTTP proxies

Several proxy tools export HAR:

• Charles Proxy — File → Export Session → HAR
• Fiddler — File → Export Sessions → HTTPArchive
• Proxyman — Export as HAR

Programmatic generation

Libraries like puppeteer and playwright can produce HAR files from automated browser sessions:

// Playwright example
const context = await browser.newContext({
  recordHar: { path: 'capture.har' }
});
// ... run your test
await context.close(); // HAR is written on close

Usage

mitm2openapi discover \
  -i capture.har \
  -o templates.yaml \
  -p "https://api.example.com"

Format is auto-detected. Use --format har to force HAR parsing if auto-detection fails.

HAR vs mitmproxy flows

Both formats produce equivalent OpenAPI specs. Choose based on your capture workflow:

• mitmproxy flows for server-side proxying, CI pipelines, and automated captures
• HAR files for browser-based testing, manual exploration, and when you already have DevTools open

Incremental parsing

HAR files are parsed incrementally — the entire JSON is not loaded into memory at once. This means memory usage stays bounded even for large HAR exports (hundreds of megabytes).

Known limitations

• Base64-encoded bodies — some HAR exporters base64-encode response bodies. Decode failures are logged as warnings and the body is skipped (not silently dropped).
• Compressed content — if the HAR exporter did not decompress response bodies, mitm2openapi sees the compressed bytes. Most browser DevTools decompress automatically.
• Timing data — HAR timing information (DNS, connect, TLS) is ignored; only request and response data is used for spec generation.