ddcutil

TLDR

List all compatible displays

$ ddcutil detect

Set brightness to 50%

$ ddcutil -d [1] setvcp 10 [50]

Increase contrast by 5%

$ ddcutil -d [1] setvcp 12 + [5]

Read all display settings

$ ddcutil -d [1] getvcp ALL

SYNOPSIS

ddcutil [options] command [arguments]

ddcutil queries and modifies display settings using the DDC/CI protocol over I2C. It can control brightness, contrast, input source, and many other monitor parameters.
Requires the i2c-dev kernel module to be loaded.

PARAMETERS

detect

List connected DDC-capable displays

getvcp feature

Read a VCP feature value

setvcp feature value

Set a VCP feature value

-d, --display num

Select display number

vcpinfo feature

Show VCP feature information

capabilities

Query display capabilities

VCP FEATURES

0x10

Brightness

0x12

Contrast

0x60

Input source

ALL

All supported features

CAVEATS

Requires the i2c-dev module: `modprobe i2c-dev`. May need to add user to i2c group. Not all monitors support DDC/CI. Some features may be read-only.