diff --git a/tools/sync.sh b/tools/sync.sh
deleted file mode 100755
index c0b768c..0000000
--- a/tools/sync.sh
+++ /dev/null
@@ -1,29 +0,0 @@
-#!/usr/bin/env bash
-
-set -euo pipefail
-
-####################
-# Mojo
-
-cd $MOJO_DIR/src
-git pull
-gclient sync
-# Build for desktop.
-./mojo/tools/mojob.py gn
-./mojo/tools/mojob.py build
-# Build for Android.
-./mojo/tools/mojob.py gn --android
-./mojo/tools/mojob.py build --android
-
-####################
-# Sky
-
-cd $SKY_DIR/src
-git pull
-gclient sync
-# Build for desktop.
-./sky/tools/gn
-ninja -C out/Debug
-# Build for Android.
-./sky/tools/gn --android
-ninja -C out/android_Debug
diff --git a/tools/sync_repos.sh b/tools/sync_repos.sh
new file mode 100755
index 0000000..51c69b1
--- /dev/null
+++ b/tools/sync_repos.sh
@@ -0,0 +1,36 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+DESKTOP="${DESKTOP:-1}"
+ANDROID="${ANDROID:-1}"
+
+####################
+# Mojo
+
+cd $MOJO_DIR/src
+git pull
+gclient sync
+if [[ "${DESKTOP}" = "1" ]]; then
+  ./mojo/tools/mojob.py gn
+  ./mojo/tools/mojob.py build
+fi
+if [[ "${ANDROID}" = "1" ]]; then
+  ./mojo/tools/mojob.py gn --android
+  ./mojo/tools/mojob.py build --android
+fi
+
+####################
+# Sky
+
+cd $SKY_DIR/src
+git pull
+gclient sync
+if [[ "${DESKTOP}" = "1" ]]; then
+  ./sky/tools/gn
+  ninja -C out/Debug
+fi
+if [[ "${ANDROID}" = "1" ]]; then
+  ./sky/tools/gn --android
+  ninja -C out/android_Debug
+fi