diff --git a/Makefile b/Makefile
index e4b2d28..20302c7 100644
--- a/Makefile
+++ b/Makefile
@@ -4,7 +4,7 @@ LOG = notqmail-${REF}-${PATCH}.log
 
 all:v
 	@test -n '${BRANCH}' -a -n '${PATCH}'
-	@make log COMMIT=${REF} PATCH=${PATCH}
+	@make log/${REF}-${PATCH}.log COMMIT=${REF} PATCH=${PATCH}
 
 everything:v
 	@xargs -I {} -n 1 make patches BRANCH={} <conf-branch
@@ -18,8 +18,6 @@ patches:v
 	@ls patch | sed 's/.patch$$//' |\
 	 xargs -I {} -n 1 make BRANCH=${BRANCH} PATCH={}
 
-log:v \
-log/${COMMIT}-${PATCH}.log
 log/${COMMIT}-${PATCH}.log:
 	@echo building $@
 	@-make build COMMIT=${COMMIT} PATCH=${PATCH} >$@.tmp 2>&1
@@ -41,6 +39,11 @@ notqmail.git:
 README.md:v
 	sh README.sh >$@
 
+brokemaster:v
+	@make patches BRANCH=${BRANCH}
+	@make patches BRANCH=master
+	sh brokemaster.sh ${BRANCH}
+
 clean:v
 	rm -rf notqmail-*/
 
diff --git a/README.sh b/README.sh
index 87d1b27..cef59b5 100644
--- a/README.sh
+++ b/README.sh
@@ -36,3 +36,50 @@ for patch in patch/*; do
 done
 
 echo "</table>"
+
+cat <<EOF
+
+Testing an individual branch/patch combo
+----------------------------------------
+```
+make BRANCH=refactoring PATCH=big-todo
+```
+
+This will produce log result in `log/$commit-big-todo.log`.
+
+Testing all patches
+-------------------
+```
+make patches BRANCH=refactoring
+```
+
+For instance, after a commit, for checking if patches still
+apply or if they need a rework.
+
+Testing all branches
+--------------------
+```
+make branches PATCH=big-todo
+```
+
+For instance, after changing a patch to check if it now works
+better on notqmail.
+
+Branches tested are listed in `conf-branch`.
+
+Testing all patches and all branches
+------------------------------------
+```
+make everything
+```
+
+Checking every merge request
+----------------------------
+```
+make brokemaster BRANCH=refactoring
+```
+
+This can be used in a script that automatically runs on merge request.
+This will return an error only if the current branch broke more patches
+than what master did already.
+EOF
diff --git a/brokemaster.sh b/brokemaster.sh
new file mode 100644
index 0000000..f2c0c95
--- /dev/null
+++ b/brokemaster.sh
@@ -0,0 +1,17 @@
+#!/bin/sh -eu
+branch=$1
+
+master=$(git -C notqmail.git rev-parse master)
+commit=$(git -C notqmail.git rev-parse "$branch")
+
+for patch in patch/*.patch; do
+	patch=$(basename "$patch" .patch)
+	if tail -n 1 "log/$master-$patch.log" | grep -qx ok; then
+		if ! tail -n 1 "log/$commit-$patch.log" | grep -qx ok; then
+			echo "$branch broke $patch"
+			brokemaster=$((brokemaster+1))
+		fi
+	fi
+done
+
+exit ${brokemaster:-0}