EnergyStarZ
Windows automatically throttles your background processes — so your foreground app stays fast. Saves battery on laptops, improves responsiveness on desktops.
What it does
EnergyStarZ watches which app you are actually using, and makes everything else get out of the way — CPU, disk and memory.
◎Foreground-aware
Listens for foreground window switches. The app you just switched to is boosted instantly; the one you left is throttled.
▤Tiered throttling
Not a single on/off switch: EcoQoS + idle priority + background I/O + low memory priority, escalating to efficiency cores when needed.
⛨Safety first
System processes, your whitelist, apps with visible windows, media playback, fullscreen video and recent apps are never throttled.
▣Tray & hotkeys
Lives in the system tray. Switch modes with Ctrl+Alt+A / P / R, or use the menu. English and Chinese included.
↺Instant restore
Switch to an app and every restriction is removed immediately. Pause or fully disable at any time — everything is restored.
◔Tiny footprint
Process enumeration via a single Toolhelp32 snapshot, batched log writes, and a background writer thread. A few MB of RAM.
How it works
Every background process is placed in a tier, and only the difference is applied when the tier changes.
Hardcoded system processes · your BypassProcessList · the foreground app · recently used apps (LRU) · processes with a visible window · likely-playing-audio processes · fullscreen / presentation mode.
EcoQoS execution-speed throttle + IDLE_PRIORITY_CLASS with PROCESS_MODE_BACKGROUND_BEGIN (which also lowers I/O and memory scheduling) + low memory priority.
Tier 1 plus pinning to efficiency cores on hybrid CPUs. Entered when the screen is off, the user has been idle, the battery is low, or the process still burns CPU after feedback measurement.
Measured, not promised
Numbers from a 16-core machine with saturated background load, measured with QueryProcessCycleTime.
Background CPU under contention
| Configuration | Cycles |
|---|---|
| Baseline | 100% |
| EcoQoS only | ~92% |
| + idle & background mode | 28% |
| + low memory priority | 3.7% |
| Restored | 100% |
Foreground responsiveness
| Wake-up latency | Before | After |
|---|---|---|
| p50 | 16.7ms | 15.1ms |
| p99 | 29.2ms | 16.2ms |
| max | 31.3ms | 16.3ms |
A 16ms p99 means a steady 60fps; 29ms means roughly one dropped frame in eight. Background processes still used 95.6% of their previous CPU — they finish their work, they just get out of the way.
Install
Windows 11 24H2 (build 26100) or later. Two builds per architecture:
Self-contained
Bundles the .NET runtime — no prerequisites. Largest download. Pick EnergyStarZ-x64-SelfContained-*.zip or the x86 build.
Framework-dependent
Requires the .NET 10 desktop runtime, but is much smaller and updates with the runtime.
Unzip anywhere and run EnergyStarZ.exe — it appears in the system tray. Edit appsettings.json next to the exe to configure, then use “Reload Configuration” in the tray menu.
Configuration
A few of the most useful keys in appsettings.json — the full list is in the README.
// appsettings.json { "AppSettings": { "Enabled": true, // master switch — false = fully dormant "InitialMode": "Auto", // Auto | Manual | Paused "ScanIntervalMinutes": 10, "EnableAutoPowerMode": false, // aggressive profile on battery "PauseOnAcPower": false, // true = stop entirely on AC "EnableEfficiencyCoreBinding": true, "EnableLowMemoryPriority": true, "DeepModeIdleMinutes": 5, "BypassProcessList": [ "myapp.exe" ] } }
FAQ
Short answers to the questions that come up most.
Does it help on a desktop, or a laptop plugged into power?
Yes — the benefit shifts from battery life to responsiveness. Background processes yield CPU, disk and memory the moment your foreground app needs them. Measured wake-up latency p99 dropped from 29.2ms to 16.2ms, while background processes still got 95.6% of their previous CPU time. On hybrid Intel desktops, efficiency-core binding also keeps the P-cores free for your game.
Will it slow down my downloads, builds or antivirus?
They run in background mode, so they finish slower when the system is busy — that is the trade-off that keeps your foreground app smooth. Anything with a visible window, anything you used recently, and anything in your whitelist is exempt. On AC power the gentlest lever (low memory priority) is off by default.
How do I turn it off completely?
Two ways: untick “Energy Management” in the tray menu (instant, restores everything), or set "Enabled": false in appsettings.json (the app starts fully dormant and also cleans up anything left over from a previous run). Paused mode is the lighter option — no throttling, but the app stays warm for an instant resume.
Is it safe? What about my music or a video call?
Critical system processes are hardcoded as protected. Processes with a visible window are never throttled, and common media/communication apps are exempt by default (configurable via AudibleProcessList). Fullscreen video and presentation mode are detected and respected. Switching to any app restores it instantly.
Why does it require Windows 11 24H2?
The efficiency-mode and power-throttling APIs it relies on only behave correctly from build 26100 onwards. On older builds the app shows a message and exits instead of misbehaving.