diff --git a/builddefs/build_keyboard.mk b/builddefs/build_keyboard.mk
index ec0336f7c3f0..6d355c9b8500 100644
--- a/builddefs/build_keyboard.mk
+++ b/builddefs/build_keyboard.mk
@@ -184,6 +184,12 @@ include $(BUILDDEFS_PATH)/converters.mk
 
 include $(BUILDDEFS_PATH)/mcu_selection.mk
 
+# PLATFORM_KEY should be detected in info.json via key 'processor' (or rules.mk 'MCU')
+ifeq ($(PLATFORM_KEY),)
+    $(call CATASTROPHIC_ERROR,Platform not defined)
+endif
+PLATFORM=$(shell echo $(PLATFORM_KEY) | tr '[:lower:]' '[:upper:]')
+
 # Find all the C source files to be compiled in subfolders.
 KEYBOARD_SRC :=
 
@@ -257,24 +263,6 @@ ifneq ("$(wildcard $(KEYBOARD_PATH_5)/$(KEYBOARD_FOLDER_5).h)","")
     FOUND_KEYBOARD_H = $(KEYBOARD_FOLDER_5).h
 endif
 
-# Determine and set parameters based on the keyboard's processor family.
-# We can assume a ChibiOS target When MCU_FAMILY is defined since it's
-# not used for LUFA
-ifdef MCU_FAMILY
-    PLATFORM=CHIBIOS
-    PLATFORM_KEY=chibios
-    FIRMWARE_FORMAT?=bin
-    OPT_DEFS += -DMCU_$(MCU_FAMILY)
-else ifdef ARM_ATSAM
-    PLATFORM=ARM_ATSAM
-    PLATFORM_KEY=arm_atsam
-    FIRMWARE_FORMAT=bin
-else
-    PLATFORM=AVR
-    PLATFORM_KEY=avr
-    FIRMWARE_FORMAT?=hex
-endif
-
 # Find all of the config.h files and add them to our CONFIG_H define.
 CONFIG_H :=
 ifneq ("$(wildcard $(KEYBOARD_PATH_5)/config.h)","")
diff --git a/builddefs/converters.mk b/builddefs/converters.mk
index 581276c2e05a..3ba0e5011671 100644
--- a/builddefs/converters.mk
+++ b/builddefs/converters.mk
@@ -19,6 +19,7 @@ ifneq ($(CONVERT_TO),)
 
     -include $(CONVERTER)/pre_converter.mk
 
+    PLATFORM_KEY = $(shell echo $(CONVERTER) | rev | cut -d "/" -f4 | rev)
     TARGET := $(TARGET)_$(CONVERT_TO)
 
     # Configure any defaults
diff --git a/data/mappings/info_rules.hjson b/data/mappings/info_rules.hjson
index b020d0c81385..c409da04c6bd 100644
--- a/data/mappings/info_rules.hjson
+++ b/data/mappings/info_rules.hjson
@@ -38,6 +38,8 @@
     "PS2_MOUSE_ENABLE": {"info_key": "ps2.mouse_enabled", "value_type": "bool"},
     "PS2_DRIVER": {"info_key": "ps2.driver"},
 
+    "PLATFORM_KEY": {"info_key": "platform_key", "to_json": false},
+
     // Items we want flagged in lint
     "CTPC": {"info_key": "_deprecated.ctpc", "deprecated": true, "replace_with": "CONVERT_TO=proton_c"},
     "CONVERT_TO_PROTON_C": {"info_key": "_deprecated.ctpc", "deprecated": true, "replace_with": "CONVERT_TO=proton_c"},
diff --git a/lib/python/qmk/info.py b/lib/python/qmk/info.py
index af3b0f309168..789d05850c97 100644
--- a/lib/python/qmk/info.py
+++ b/lib/python/qmk/info.py
@@ -751,6 +751,7 @@ def arm_processor_rules(info_data, rules):
     """
     info_data['processor_type'] = 'arm'
     info_data['protocol'] = 'ChibiOS'
+    info_data['platform_key'] = 'chibios'
 
     if 'STM32' in info_data['processor']:
         info_data['platform'] = 'STM32'
@@ -758,6 +759,7 @@ def arm_processor_rules(info_data, rules):
         info_data['platform'] = rules['MCU_SERIES']
     elif 'ARM_ATSAM' in rules:
         info_data['platform'] = 'ARM_ATSAM'
+        info_data['platform_key'] = 'arm_atsam'
 
     return info_data
 
@@ -767,6 +769,7 @@ def avr_processor_rules(info_data, rules):
     """
     info_data['processor_type'] = 'avr'
     info_data['platform'] = rules['ARCH'] if 'ARCH' in rules else 'unknown'
+    info_data['platform_key'] = 'avr'
     info_data['protocol'] = 'V-USB' if info_data['processor'] in VUSB_PROCESSORS else 'LUFA'
 
     # FIXME(fauxpark/anyone): Eventually we should detect the protocol by looking at PROTOCOL inherited from mcu_selection.mk:
diff --git a/platforms/arm_atsam/bootloader.mk b/platforms/arm_atsam/bootloader.mk
index 1ec42edeb68f..7e503bdca9d7 100644
--- a/platforms/arm_atsam/bootloader.mk
+++ b/platforms/arm_atsam/bootloader.mk
@@ -27,6 +27,8 @@
 # the respective file under `platforms/<PLATFORM>/bootloaders/custom.c` to see
 # which functions may be overridden.
 
+FIRMWARE_FORMAT?=bin
+
 ifeq ($(strip $(BOOTLOADER)), custom)
     OPT_DEFS += -DBOOTLOADER_CUSTOM
     BOOTLOADER_TYPE = custom
diff --git a/platforms/avr/bootloader.mk b/platforms/avr/bootloader.mk
index 63fe635d96a0..36e3fd83db63 100644
--- a/platforms/avr/bootloader.mk
+++ b/platforms/avr/bootloader.mk
@@ -37,6 +37,8 @@
 # BOOTLOADER_SIZE can still be defined manually, but it's recommended
 # you add any possible configuration to this list
 
+FIRMWARE_FORMAT?=hex
+
 ifeq ($(strip $(BOOTLOADER)), custom)
     OPT_DEFS += -DBOOTLOADER_CUSTOM
     BOOTLOADER_TYPE = custom
diff --git a/platforms/chibios/bootloader.mk b/platforms/chibios/bootloader.mk
index 85f186606228..481241234402 100644
--- a/platforms/chibios/bootloader.mk
+++ b/platforms/chibios/bootloader.mk
@@ -36,6 +36,8 @@
 # the respective file under `platforms/<PLATFORM>/bootloaders/custom.c` to see
 # which functions may be overridden.
 
+FIRMWARE_FORMAT?=bin
+
 ifeq ($(strip $(BOOTLOADER)), custom)
     OPT_DEFS += -DBOOTLOADER_CUSTOM
     BOOTLOADER_TYPE = custom
diff --git a/platforms/chibios/platform.mk b/platforms/chibios/platform.mk
index b2a8ec89e138..fd4c6bd2e571 100644
--- a/platforms/chibios/platform.mk
+++ b/platforms/chibios/platform.mk
@@ -442,6 +442,9 @@ LDFLAGS  += $(SHARED_LDFLAGS) $(SHARED_LDSYMBOLS) $(TOOLCHAIN_LDFLAGS) $(TOOLCHA
 # Tell QMK that we are hosting it on ChibiOS.
 OPT_DEFS += -DPROTOCOL_CHIBIOS
 
+# And what flavor of MCU
+OPT_DEFS += -DMCU_$(MCU_FAMILY)
+
 # ChibiOS supports synchronization primitives like a Mutex
 OPT_DEFS += -DPLATFORM_SUPPORTS_SYNCHRONIZATION