In many triggers, actions and constraints you will have the option to configure some textual fields. Often you will find a button next to the text entry field that contains the "..." label. This button will display a complete list of "magic text" fields that are available in the context that is being used.

The magic text allows some other value to be substituted at the point of invocation, rather than standard static text that will never changed. For example it's possible to add and action that reference a variable via magic text and that variable's value will be substituted at the point that action is run.
*Full list of static magic text options NOT dependant on triggers.
*List of additional magic text dependant on triggers
MacroDroid mode

-Stopwatches-

-Variables users have created-

String variable length

String variable value

Dictionary/Array size

New line

Foreground app name

Foreground app package

Current brightness

Current brightness (Android 9+ alternative)

Screen timeout (seconds)

Current battery %

Battery temp ºC

Power (on/off)

Clipboard text

Current IP address

Current IP address (V6)

Wifi SSID

Wifi signal strength

Cell tower signal strength

Day of the week

Day of the month

Week of year

Month

Month (as digit)

Year

Hour of day

Hour of day (12h)

Minute

Second

am/pm

System time

Webhook Base Url

System setting (System)

System setting (Global)

System setting (Secure)

Cell connection type

Mobile country code

Mobile network code

Location area code

IMEI

Cell id

Last known location (lat,lon)

Last known location (lat)

Last known location (lon)

Last known location (altitude)

Last known location (accuracy meters)

Last known location (link)

Last known location (time)

Last location speed (kmh)

Last location speed (mph)

Current volume (Alarm)

Current volume (Media / Music)

Current volume (Ringer)

Current volume (Notification)

Current volume (System sounds)

Current volume (Voice call)

Current volume (Bluetooth voice)

Macro name

Macro category

Device serial

Device name

Device uptime

Device uptime (s)

Device manufacturer

Device model

Macrodroid version

Macrodroid is pro

Android version

Android  version (SDK level)

Sim operator name

Screen resolution

Screen resolution (X)

Screen resolution (Y)

RAM (Total)

RAM (available)

Storage total (external)

Storage free (external)

Storage total (internal)

Storage free (external)
List of additional magic text dependant on triggers:

App installed/updated/removed trigger:
Application name
Application package

Application opened/closed trigger:
Application name

Call triggers:
Call name
Call number

Bluethooth (Device connected or device disconnected): 
Bluethooth device name

SMS recived:
Incoming SMS contact
incoming SMS message
incoming SMS number

Logcat:
Logcat entry line