diff --git a/Makefile b/Makefile
index f51617d..52b644f 100644
--- a/Makefile
+++ b/Makefile
@@ -3,8 +3,8 @@ CHANNEL=stable
 clean:
 	rm -rf *.img *.model *.manifest
 
-%.model: boards/%.json # sign a model file
-	cat boards/HEAD.json $< boards/FOOT.json | sed "s|TIMESTAMP|$(shell date -Iseconds --utc)|g" | snap sign -k default > $@
+%.model: boards/%.yaml # sign a model file
+	cat definition.yaml $< | python -c "import sys, yaml, json; json.dump(yaml.load(sys.stdin), sys.stdout, indent=2)" | sed "s|TIMESTAMP|$(shell date -Iseconds --utc)|g" | snap sign -k default > $@
 %.img: %.model # build an image
 	sudo ubuntu-image snap -o $@ -c $(CHANNEL) $<
 
diff --git a/boards/FOOT.json b/boards/FOOT.json
deleted file mode 100644
index 40da745..0000000
--- a/boards/FOOT.json
+++ /dev/null
@@ -1,5 +0,0 @@
-  "required-snaps": ["hello", "hello-world", "nextcloud", "lxd"],
-  "authority-id": "7xN2sMCILuFk10e6DxrTrQWprdmV0Vi9",
-  "brand-id": "7xN2sMCILuFk10e6DxrTrQWprdmV0Vi9",
-  "timestamp": "TIMESTAMP"
-}
diff --git a/boards/HEAD.json b/boards/HEAD.json
deleted file mode 100644
index c4117b2..0000000
--- a/boards/HEAD.json
+++ /dev/null
@@ -1,4 +0,0 @@
-{
-  "type": "model",
-  "series": "16",
-  "model": "hub",
diff --git a/boards/amd64.json b/boards/amd64.json
deleted file mode 100644
index 12b3b8c..0000000
--- a/boards/amd64.json
+++ /dev/null
@@ -1,3 +0,0 @@
-  "architecture": "amd64",
-  "gadget": "joule",
-  "kernel": "joule-linux",
diff --git a/boards/amd64.yaml b/boards/amd64.yaml
new file mode 100644
index 0000000..9c69dd6
--- /dev/null
+++ b/boards/amd64.yaml
@@ -0,0 +1,3 @@
+architecture: amd64
+gadget: joule
+kernel: joule-linux
diff --git a/boards/rpi2.json b/boards/rpi2.json
deleted file mode 100644
index e99bc6b..0000000
--- a/boards/rpi2.json
+++ /dev/null
@@ -1,3 +0,0 @@
-  "architecture": "armhf",
-  "gadget": "pi2",
-  "kernel": "pi2-kernel",
diff --git a/boards/rpi2.yaml b/boards/rpi2.yaml
new file mode 100644
index 0000000..180b7e9
--- /dev/null
+++ b/boards/rpi2.yaml
@@ -0,0 +1,3 @@
+architecture: armhf
+gadget: pi2
+kernel: pi2-kernel
diff --git a/boards/rpi3.json b/boards/rpi3.json
deleted file mode 100644
index d7384de..0000000
--- a/boards/rpi3.json
+++ /dev/null
@@ -1,4 +0,0 @@
-  "architecture": "armhf",
-  "gadget": "pi2",
-  "kernel": "pi3-kernel",
-
diff --git a/boards/rpi3.yaml b/boards/rpi3.yaml
new file mode 100644
index 0000000..470e639
--- /dev/null
+++ b/boards/rpi3.yaml
@@ -0,0 +1,4 @@
+architecture: armhf
+gadget: pi3
+kernel: pi2-kernel
+
diff --git a/definition.yaml b/definition.yaml
new file mode 100644
index 0000000..c0da4c2
--- /dev/null
+++ b/definition.yaml
@@ -0,0 +1,12 @@
+# basic
+type: model
+series: "16"
+model: hub
+# snaps to be preinstalled:
+required-snaps:
+ - nextcloud # just for proof-of-concept
+# authority meta
+authority-id: 7xN2sMCILuFk10e6DxrTrQWprdmV0Vi9
+brand-id: 7xN2sMCILuFk10e6DxrTrQWprdmV0Vi9
+# timestamp gets filled in automatically
+timestamp: TIMESTAMP