Request Cycle Monitor & Modifier

A personal Windows privacy tool that lets you see, edit, and block the network requests your apps make. It runs a local decrypting proxy (the same mechanism as Fiddler / Charles / mitmproxy), attributes each request to the app that made it, and gives you a UI to inspect traffic, block spyware/telemetry, and rewrite what you send and receive. When you close the window it keeps running in the system tray (bottom-right notification area).

This is a defensive tool for your own machine. It only inspects traffic on this PC. Decrypting HTTPS requires trusting a local certificate — that step is explicit, opt-in, and fully reversible.

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What it does

• Monitor — a live feed of every request/response: time, app, method, host, path, status, and whether it was passed / blocked / modified. Click any row to see full headers and bodies.
• Modify — rules to strip or set headers, find-and-replace in request or response bodies, redirect, or delay. Plus edit & replay any captured request.
• Block — curated block lists for Windows/Microsoft telemetry, ad networks, social trackers, and third-party app telemetry, plus your own custom hosts and rules.
• Current-app-only focus — scope monitoring or enforcement to just the app you currently have in the foreground.
• Logs — a timestamped session log every time you launch the monitor, plus a system-wide activity log recording when apps launch and what they connected to.
• Tray — closing the window minimizes to the tray and keeps filtering; quitting cleanly restores your Windows proxy settings.

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Architecture

Electron UI  <-- WebSocket (live feed) / REST (control) -->  Python engine
  app/                       127.0.0.1 only                    engine/
  • window + tray                                              • mitmproxy proxy + MITM
  • Live/Rules/Logs/                                           • FastAPI control plane
    Activity/Settings                                          • rule engine + block lists
                                                               • per-app attribution
                                                               • process/network monitors
                                                               • system-proxy + cert mgmt

The Electron shell spawns the Python engine, waits for its ready signal, and then connects. All engine endpoints are bound to 127.0.0.1.

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Requirements

• Windows 10/11
• Python 3.12 (the py -3.12 launcher) — used to build engine/.venv
• Node.js (for Electron)

Both are already present if you ran this from the machine it was built on.

Setup (one time)

Double-click setup.cmd, or from a terminal:

setup.cmd

This creates engine/.venv, installs the Python dependencies (mitmproxy, fastapi, uvicorn, psutil, pywin32), and installs Electron.

Run

Double-click start.vbs (recommended — opens only the GUI, no console window), or start.cmd which delegates to it. Both request administrator rights (needed for per-app firewall blocking); if you decline, the app still runs with limited blocking.

Tip: right-click start.vbs → Send to → Desktop (create shortcut), rename it to "Request Cycle Monitor", and set its icon to app/assets/icon-256.png for a clean one-click launcher.

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First run — trust the HTTPS certificate

To read/modify HTTPS (not just plain HTTP), Windows must trust the proxy's local certificate:

1. Launch the app and leave it running for a few seconds (this generates the certificate at %USERPROFILE%\.mitmproxy\).
2. Go to Settings → HTTPS certificate → Install & trust.
3. Accept the Windows security prompt that appears.

The status pill at the top will switch to certificate trusted.

To remove it later: Settings → Remove trust (or run certutil -user -delstore Root mitmproxy).

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Using it

• Settings → Proxy: the system proxy is on by default now, so traffic is intercepted from launch. Install & trust the certificate first (below) or HTTPS sites will show certificate warnings. Turning it off (or quitting) restores your previous Windows proxy settings.
• Rules & Blocking: toggle block-list categories, add custom hosts, and create rules (block / edit headers / find-replace body / redirect / delay), scoped to all apps, a specific .exe, or the current foreground app.
• Settings → Focus: Only the app I'm using limits the tool to the foreground app. Choose Enforce (rules apply only to that app; feed shows everything) or Monitor (feed shows only that app).
• Logs / Activity: browse past sessions and system activity. Open logs folder reveals the raw .jsonl files under logs/.

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Where things are stored

config/settings.json        your preferences
config/rules.json           your rules
config/proxy_backup.json    saved Windows proxy state (only exists while active)
logs/sessions/*.jsonl       one file per monitor run
logs/activity/YYYY-MM-DD.jsonl   app launches + connections per day

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Limitations (please read)

• Proxy-aware traffic only. It intercepts apps that honor the Windows system proxy (browsers and most well-behaved apps). Apps that ignore the proxy, or use certificate pinning, won't be intercepted. Kernel-level enforcement (WinDivert) is a possible future upgrade.
• Per-app attribution is best-effort. Very short-lived connections can close before we map their source port to a process.
• Restore safety. If the engine ever crashes while the system proxy is redirected, it restores your original settings automatically on the next launch (config/proxy_backup.json).

Running the engine on its own (for debugging)

engine\.venv\Scripts\python.exe engine\main.py --api-port 8788 --proxy-port 8080 --no-system-proxy

--no-system-proxy runs the local proxy without changing your Windows settings.

Troubleshooting

• Certificate won't trust — make sure the app ran once so the CA exists at %USERPROFILE%\.mitmproxy\mitmproxy-ca-cert.cer, then retry Install & trust.

• No traffic in the feed — confirm Route system traffic through the monitor is on (Settings) and the top pill shows system proxy → monitor.

• Port already in use — set RCM_API_PORT / RCM_PROXY_PORT environment variables before launching to change the ports.

  Application made by Claude