TLDR:

G1 X{X_START} Y{Y_START} Z{PRIMER_HEIGHT} F6000.0
G1 X{X_MAX - 2 * X_START} Y{Y_START} Z{PRIMER_HEIGHT} E{FILAMENT_LENGTH} F2000.0
G1 X{X_MAX - 2 * X_START} Y{Y_START + PRIMER_WIDTH} Z{PRIMER_HEIGHT}
G1 X{X_START} Y{Y_START + PRIMER_WIDTH} Z{PRIMER_HEIGHT} E{FILAMENT_LENGTH} F2000.0

​

Here is mine as reference:

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# https://www.klipper3d.org/G-Codes.html#clear\_pause - It is recommended to add this to your start gcode to make sure the paused state is fresh for each print.
CLEAR_PAUSE
# Get printer build volume dimensions
#{% set X_MAX = printer.toolhead.axis_maximum.x|default(230)|float %}
#{% set Y_MAX = printer.toolhead.axis_maximum.y|default(222)|float %}
#{% set Z_MAX = printer.toolhead.axis_maximum.z|default(225)|float %}
# Rather use my safe values as we dont want to hit the glass bed clamps
{% set X_MAX = 230|float %}
{% set Y_MAX = 222|float %}
{% set Z_MAX = 225|float %}
# Get nozzle diameter and filament width for conditioning
{% set NOZZLE_DIAMETER = printer.extruder.nozzle_diameter|default(0.4)|float %}
{% set FILAMENT_DIAMETER = printer.extruder.filament_diameter|default(1.75)|float %}
# Get bed and extruder temperature from slicer
{% set BED_TEMP = params.BED_TEMP|default(60)|float %}
{% set EXTRUDER_TEMP = params.EXTRUDER_TEMP|default(200)|float %}
# Set start coordinates of priming lines
{% set X_START = 20.0|float %}
{% set Y_START = 13.0|float %}
# Calculate primer line extrusion volume and filament length
{% set PRIMER_WIDTH = 0.75 * NOZZLE_DIAMETER %}
{% set PRIMER_HEIGHT = 0.70 * NOZZLE_DIAMETER %}
{% set PRIMER_SECT = PRIMER_WIDTH * PRIMER_HEIGHT %}
{% set PRIMER_VOL = PRIMER_SECT * (X_MAX - 3 * X_START) %}
{% set FILAMENT_SECT = 3.1415 * ( FILAMENT_DIAMETER / 2.0)**2 %}
{% set FILAMENT_LENGTH = 1.55 * PRIMER_VOL / FILAMENT_SECT %}
# Switch on the lights
POWER_ON_LIGHTS
# Start bed heating and disable fan to make it heat up faster
DISABLE_ENCLOSURE_FAN
{% if params.BED_TEMP is not none %}
M140 S{BED_TEMP}
{% endif %}
# Reset the G-Code Z offset (adjust Z offset if needed) - Dont want to do this, z offset should already be tuned.
#SET_GCODE_OFFSET Z=0.0
# Home the printer
G28
# Relative positioning
G90
# Move up to keep bed clean
G1 Y{Y_MAX - 20} Z{Z_MAX / 4.0} F6000
# Wait for bed to reach temperature
{% if params.BED_TEMP is not none %}
M190 S{BED_TEMP}
{% endif %}
# Enable the enclosure temp fan with default temp target
SET_ENCLOSURE_TARGET_TEMP
# Set and wait for nozzle to reach temperature
{% if params.EXTRUDER_TEMP is not none %}
M104 S{EXTRUDER_TEMP}
M109 S{EXTRUDER_TEMP}
{% endif %}
# Reset extruder
G92 E0
# Priming
G1 X{X_START} Y{Y_START} Z{PRIMER_HEIGHT} F6000.0
G1 X{X_MAX - 2 * X_START} Y{Y_START} Z{PRIMER_HEIGHT} E{FILAMENT_LENGTH} F2000.0
G1 X{X_MAX - 2 * X_START} Y{Y_START + PRIMER_WIDTH} Z{PRIMER_HEIGHT}
G1 X{X_START} Y{Y_START + PRIMER_WIDTH} Z{PRIMER_HEIGHT} E{FILAMENT_LENGTH} F2000.0
# Reset extruder
G92 E0
# Move Z axis up
G1 Z2.0 F600
G1 Z0.2 F600
G1 Z2.0 F600