Monitor KVM Switch

Automatically switches your monitors' physical inputs (DDC/CI) to follow Synergy as you move your mouse between computers — so when you switch which PC has keyboard/mouse focus, the monitors switch to show that PC too, without touching a physical KVM button.

It watches Synergy's log file for screen-switch events and drives each monitor's Input Select (VCP 0x60) over DDC/CI accordingly.

• monitor_kvm_switch.exe — the background watcher. Runs from the tray, tails the Synergy log, and does the actual switching.
• gui.exe — the settings editor. Lets you map hosts to monitor inputs, test values live, identify which physical monitor is which, and edit everything monitor_kvm_switch.exe reads.

Each can launch the other: the GUI has a Launch watcher button, and the tray has an Open Settings item.

Requirements

• Windows
• Monitors that support DDC/CI (enable it in the monitor's OSD if it's off)
• Synergy 3 (or compatible fork) already set up and logging to C:\Program Files\Synergy\synergy-daemon.log (configurable)

First-time setup

1. Run monitor_kvm_switch.exe once with no config.toml present — it drops into an interactive console wizard: it lists every Synergy screen name it's ever seen in the log, asks which monitors (if any) each host needs to switch, and tests each candidate DDC/CI value by switching to it for 10 seconds so you can visually confirm before it's recorded.
2. Once config.toml exists, running the exe again starts the real watcher instead.
3. For anything beyond the initial setup, use gui.exe — it's the fuller editor (see below) and is what you'll come back to most.

Config lives at %ProgramData%\MonitorKvmSwitch\config.toml, shared by both binaries.

Using the GUI

• Hosts sidebar — every host you've configured, with a status dot: green (fully decided for every monitor), yellow (partial), gray (empty). Hosts seen in the Synergy log but not yet configured show separately so you can add them with one click.
• Settings card — settle delay (ms a screen must stay active before switching; 0 = instant) and the Synergy log path.
• Monitors card — one box per detected monitor: name (editable, auto-filled from EDID where the monitor provides it), physical position (left/right/top/bottom, from Windows), full serial number, manufacturer code, current input, and an Identify button.
• Host detail — for the selected host, each monitor is one of three states:
  • not set — undecided; Use current records whatever the monitor is already showing (for the host you're currently on), or Test N switches to a candidate value for 10 seconds so you can confirm it before committing
  • no switch needed — a deliberate decision that this host doesn't need this monitor to change (e.g. it has its own dedicated screen)
  • input N — an active mapping, with a checkbox to enable/disable it without losing the value
• Identify — pops up a real window on the actual physical monitor for 5 seconds, showing its index, name, current input + connection type (e.g. "Input 15 • DisplayPort 1"), and full serial number. This is the reliable way to tell two identical monitors apart — position/EDID detection are both best-effort guesses, Identify is ground truth.

config.toml

log_path = 'C:\Program Files\Synergy\synergy-daemon.log'
settle_ms = 0

[monitor_names]
0 = "ASUS VP28U"
1 = "ASUS VP28U"

[inputs.xxvii-253e9ec9]
0 = 15
1 = 15

[inputs.neon-88954047]
1 = 18

[disabled]
# host = ["monitor index", ...]  -- has a value but temporarily off

[no_switch]
surface3-65ce4094 = ["0", "1"]

Keys under [inputs.*], [disabled], and [no_switch] are monitor indices, not names — this matters because two identical monitors will often get the same auto-detected name, and names were the original (buggy) join key in an earlier version of this schema. monitor_names is purely a display label and can safely be duplicated.

Host names must be the literal Synergy client ID as it appears in the log (e.g. xxvii-253e9ec9), not a nickname.

Tray menu

Grouped by host, since the underlying tray library (tray-item) has no submenu support:

Watching for switches...
---
xxvii-253e9ec9                    (grayed header, not clickable)
  [🟢] Monitor 0: ASUS VP28U
  [🟢] Monitor 1: ASUS VP28U
---
surface3-65ce4094
  [🟢] Monitor 0: ASUS VP28U
  [⚪] Monitor 1: ASUS VP28U
---
Reload config
Open Settings
Open config folder
---
Quit

Clicking a monitor toggles switching for that host+monitor combination for the current session only (not saved) — for a permanent change, use the GUI's checkbox and save.

Known limitations

• Tray submenus/icons: tray-item supports neither. The host grouping is a flat list with grayed headers and indentation, not real nested menus; the 🟢/⚪ circles are the closest thing to per-item icons this crate allows.
• VCP code 19+ isn't labeled: codes 1–18 are standardized by MCCS and shown with real names (DisplayPort, HDMI, etc); anything above that varies by manufacturer, so it's deliberately left unlabeled rather than guessed.
• EDID name/serial are optional fields: not every monitor sets them. When absent, the name falls back to monitor_N (editable) and the serial/manufacturer fields just don't show.
• Position and monitor-index correlation are both ordinal guesses: ddc-hi's enumeration order, EnumDisplayMonitors' order, and the registry's EDID enumeration order are three independent mechanisms that usually — but aren't guaranteed to — agree on which index is which physical monitor. Identify is the way to verify this for certain.

Troubleshooting

• Nothing switches: check the host name in config.toml matches the Synergy log's client ID exactly (case-sensitive).
• Wrong monitor switches, or one switches when it shouldn't: use Identify on both monitors and re-check which index is actually which physical screen before trusting position labels.
• Tray icon shows the generic Windows icon instead of the custom one: harmless fallback — check the console/log output for why LoadImageW failed (usually a missing/corrupted tray_icon.ico next to config.toml, which gets rewritten fresh on every launch anyway).