Network Limiter

Per-process network bandwidth limiter for Windows. Throttle the download and upload speed of individual applications (by PID) in real time, built on WinDivert (pydivert) and psutil.

Ships as two things:

• A library (network_limiter) — a clean, GUI-free API you can drive from your own Python code.
• A desktop GUI (optional [gui] extra) — a live per-process traffic table with toolbar, status bar, and inline limit editing.

⚠️ Windows only. WinDivert is a Windows kernel driver and requires Administrator privileges.

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Features

• Throttle download and/or upload speed per process (KB/s).
• Live per-application throughput monitoring.
• Works with TCP and UDP, including QUIC / HTTP3 (wildcard-bound UDP fallback).
• Use it as a library (no GUI dependency) or as a desktop app.
• Modern dark-themed GUI: toolbar, search, status bar with admin indicator, and double-click inline limit editing.

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Requirements

• Windows 10 / 11
• Python 3.10+
• Administrator privileges (WinDivert)

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Installation

As a library (no GUI)

pip install network-limiter

With the desktop GUI

pip install "network-limiter[gui]"

From source

git clone https://github.com/EmperorHeyman/network-limiter.git
cd network-limiter
pip install ".[gui]"        # or: pip install .   (library only)

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Library usage

The core engine is NetworkLimiter. It runs its capture/throttle loop on a background thread, so you start it, set limits, and stop it whenever you like.

from network_limiter import NetworkLimiter, find_pids_by_name, list_processes

# 1. List running processes
for proc in list_processes()[:5]:
    print(proc["pid"], proc["name"])

# 2. Start the engine (needs Administrator)
limiter = NetworkLimiter()
limiter.start()

# 3. Limit every Chrome process to 500 KB/s down, 100 KB/s up
for pid in find_pids_by_name("chrome.exe"):
    limiter.set_limit(pid, down_kbs=500, up_kbs=100)

# 4. Inspect current limits
print(limiter.get_limits())

# 5. Remove limits and stop
limiter.clear_limit()      # clear all (or pass a pid to clear one)
limiter.stop()

Context manager

from network_limiter import NetworkLimiter

with NetworkLimiter() as limiter:
    limiter.set_limit(1234, down_kbs=1000)   # 0 = unlimited for that direction
    input("Throttling PID 1234... press Enter to stop")
# engine stops automatically on exit

Live stats via callbacks

Callbacks fire on the engine's background thread (marshal to your UI thread if needed):

from network_limiter import NetworkLimiter

def on_stats(rows):
    for row in rows[:3]:
        print(f"{row['name']:<25} ↓{row['down_kbs']:.1f} ↑{row['up_kbs']:.1f} KB/s")

limiter = NetworkLimiter(
    on_stats=on_stats,
    on_status=print,
    on_error=lambda msg: print("ERROR:", msg),
)
limiter.start()

API summary

Member	Description
NetworkLimiter(packet_filter, on_stats, on_status, on_error, on_limits_changed)	Create an engine.
.start() / .stop(timeout=5.0)	Start / stop the background loop.
.set_limit(pid, down_kbs=0, up_kbs=0, name=None)	Throttle a PID (0 = unlimited).
.clear_limit(pid=None)	Remove one limit, or all when pid is None.
.get_limits() / .get_stats()	Current limits / latest throughput.
.running	Whether the loop is alive.
list_processes()	[{"pid", "name"}, ...] snapshot.
find_pids_by_name(name)	PIDs whose name matches (substring, case-insensitive).

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GUI usage

After installing with the [gui] extra:

network-limiter

or

python -m network_limiter

The app relaunches itself elevated via UAC. Double-click a Limit ↓ or Limit ↑ cell to throttle that app inline, use the toolbar to clear limits, and the search box to filter. The status bar shows the monitor state and whether you are running as Administrator.

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Build a standalone .exe

A PyInstaller spec is included. It bundles the WinDivert driver and requests elevation (uac_admin).

pip install ".[dev]"
pyinstaller network_limiter.spec
# -> dist/network_limiter.exe

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How it works

WinDivert intercepts packets in the kernel and hands them to user space. network_limiter maps each packet to a PID via psutil connection tables (with a port-only fallback for wildcard-bound UDP sockets used by QUIC/HTTP3), then delays packets for throttled PIDs using a sliding-window rate calculation before re-injecting them. Unthrottled traffic passes straight through.

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License

MIT © 2026 Lukáš Peterek