diff --git a/makefiles/tools/adafruit-nrfutil.inc.mk b/makefiles/tools/adafruit-nrfutil.inc.mk
index eea4ba8024..73c395faf2 100644
--- a/makefiles/tools/adafruit-nrfutil.inc.mk
+++ b/makefiles/tools/adafruit-nrfutil.inc.mk
@@ -1,6 +1,6 @@
 FLASHFILE = $(HEXFILE)
 FLASHDEPS += $(HEXFILE).zip
-FLASHER = adafruit-nrfutil
+FLASHER ?= adafruit-nrfutil
 FFLAGS = dfu serial --port=${PORT} --baudrate=${BAUD} --touch=1200 --package=$(HEXFILE).zip --singlebank
 
 %.hex.zip: %.hex
diff --git a/makefiles/tools/avrdude.inc.mk b/makefiles/tools/avrdude.inc.mk
index 85bb78492f..29f9371f10 100644
--- a/makefiles/tools/avrdude.inc.mk
+++ b/makefiles/tools/avrdude.inc.mk
@@ -1,8 +1,8 @@
-FLASHER = avrdude
+FLASHER ?= avrdude
 DIST_PATH = $(BOARDDIR)/dist
 AVARICE_PATH = $(RIOTTOOLS)/avarice
 DEBUGSERVER_PORT = 4242
-DEBUGSERVER = $(AVARICE_PATH)/debug_srv.sh
+DEBUGSERVER ?= $(AVARICE_PATH)/debug_srv.sh
 # Allow choosing debugger hardware via AVR_DEBUGDEVICE, default to Atmel ICE,
 # which is compatible to all AVR devices and since the AVR Dragon is no longer
 # produced, the least expensive option
@@ -15,8 +15,8 @@ else
   # Use JTAG as protocol for debugging
   DEBUGPROTO := -j $(AVR_DEBUGINTERFACE)
 endif
-DEBUGSERVER_FLAGS = "$(AVR_DEBUGDEVICE) $(DEBUGPROTO) :$(DEBUGSERVER_PORT)"
-DEBUGGER_FLAGS = "-x $(AVARICE_PATH)/gdb.conf $(ELFFILE)"
+DEBUGSERVER_FLAGS ?= "$(AVR_DEBUGDEVICE) $(DEBUGPROTO) :$(DEBUGSERVER_PORT)"
+DEBUGGER_FLAGS ?= "-x $(AVARICE_PATH)/gdb.conf $(ELFFILE)"
 DEBUGGER = "$(AVARICE_PATH)/debug.sh" $(DEBUGSERVER_FLAGS) $(AVARICE_PATH) $(DEBUGSERVER_PORT)
 
 AVRDUDE_PROGRAMMER_FLAGS = -p $(subst atmega,m,$(CPU))
diff --git a/makefiles/tools/bmp.inc.mk b/makefiles/tools/bmp.inc.mk
index 208793e211..47503b9722 100644
--- a/makefiles/tools/bmp.inc.mk
+++ b/makefiles/tools/bmp.inc.mk
@@ -1,5 +1,5 @@
 FLASHER ?= $(RIOTTOOLS)/bmp/bmp.py
-DEBUGGER = $(RIOTTOOLS)/bmp/bmp.py
+DEBUGGER ?= $(RIOTTOOLS)/bmp/bmp.py
 RESET ?= $(RIOTTOOLS)/bmp/bmp.py
 
 FLASHFILE ?= $(ELFFILE)
diff --git a/makefiles/tools/cc2538-bsl.inc.mk b/makefiles/tools/cc2538-bsl.inc.mk
index cb9bcf7c36..6b55640338 100644
--- a/makefiles/tools/cc2538-bsl.inc.mk
+++ b/makefiles/tools/cc2538-bsl.inc.mk
@@ -1,5 +1,5 @@
 FLASHFILE ?= $(BINFILE)
-FLASHER = $(RIOTTOOLS)/cc2538-bsl/cc2538-bsl.py
+FLASHER ?= $(RIOTTOOLS)/cc2538-bsl/cc2538-bsl.py
 FFLAGS_OPTS ?=
 PROG_BAUD ?= 500000	# default value in cc2538-bsl
 
diff --git a/makefiles/tools/jlink.inc.mk b/makefiles/tools/jlink.inc.mk
index 149a6183d6..83a7c0c482 100644
--- a/makefiles/tools/jlink.inc.mk
+++ b/makefiles/tools/jlink.inc.mk
@@ -1,6 +1,6 @@
 FLASHER = $(RIOTTOOLS)/jlink/jlink.sh
-DEBUGGER = $(RIOTTOOLS)/jlink/jlink.sh
-DEBUGSERVER = $(RIOTTOOLS)/jlink/jlink.sh
+DEBUGGER ?= $(RIOTTOOLS)/jlink/jlink.sh
+DEBUGSERVER ?= $(RIOTTOOLS)/jlink/jlink.sh
 RESET ?= $(RIOTTOOLS)/jlink/jlink.sh
 
 FLASHFILE ?= $(BINFILE)
diff --git a/makefiles/tools/openocd.inc.mk b/makefiles/tools/openocd.inc.mk
index e2c4324db5..a67db84f1b 100644
--- a/makefiles/tools/openocd.inc.mk
+++ b/makefiles/tools/openocd.inc.mk
@@ -1,6 +1,6 @@
 FLASHER ?= $(RIOTTOOLS)/openocd/openocd.sh
-DEBUGGER = $(RIOTTOOLS)/openocd/openocd.sh
-DEBUGSERVER = $(RIOTTOOLS)/openocd/openocd.sh
+DEBUGGER ?= $(RIOTTOOLS)/openocd/openocd.sh
+DEBUGSERVER ?= $(RIOTTOOLS)/openocd/openocd.sh
 RESET ?= $(RIOTTOOLS)/openocd/openocd.sh
 
 FLASHFILE ?= $(ELFFILE)
diff --git a/makefiles/tools/pyocd.inc.mk b/makefiles/tools/pyocd.inc.mk
index c23ff60057..087ab9b118 100644
--- a/makefiles/tools/pyocd.inc.mk
+++ b/makefiles/tools/pyocd.inc.mk
@@ -1,6 +1,6 @@
 FLASHER ?= $(RIOTBASE)/dist/tools/pyocd/pyocd.sh
-DEBUGGER = $(RIOTBASE)/dist/tools/pyocd/pyocd.sh
-DEBUGSERVER = $(RIOTBASE)/dist/tools/pyocd/pyocd.sh
+DEBUGGER ?= $(RIOTBASE)/dist/tools/pyocd/pyocd.sh
+DEBUGSERVER ?= $(RIOTBASE)/dist/tools/pyocd/pyocd.sh
 RESET ?= $(RIOTBASE)/dist/tools/pyocd/pyocd.sh
 
 FLASH_TARGET_TYPE ?=
diff --git a/makefiles/tools/uniflash.inc.mk b/makefiles/tools/uniflash.inc.mk
index 5845044063..2e66f3d921 100644
--- a/makefiles/tools/uniflash.inc.mk
+++ b/makefiles/tools/uniflash.inc.mk
@@ -29,9 +29,9 @@ endif
 
 CCS_PATH ?= "CCS_PATH unconfigured"
 # configure the debug server
-DEBUGSERVER = $(CCS_PATH)/ccs/ccs_base/common/uscif/gdb_agent_console
-DEBUGSERVER_FLAGS = -p 3333 $(UNIFLASH_CONFIG_DAT)
+DEBUGSERVER ?= $(CCS_PATH)/ccs/ccs_base/common/uscif/gdb_agent_console
+DEBUGSERVER_FLAGS ?= -p 3333 $(UNIFLASH_CONFIG_DAT)
 
 # configure the debugging tool
-DEBUGGER = $(PREFIX)gdb
-DEBUGGER_FLAGS = -x $(UNIFLASH_CONFIG_GDB) $(ELFFILE)
+DEBUGGER ?= $(PREFIX)gdb
+DEBUGGER_FLAGS ?= -x $(UNIFLASH_CONFIG_GDB) $(ELFFILE)