diff --git a/cmd/dkl-store-upload/main.go b/cmd/dkl-store-upload/main.go
index fd04351..f6ddf6c 100644
--- a/cmd/dkl-store-upload/main.go
+++ b/cmd/dkl-store-upload/main.go
@@ -30,6 +30,8 @@ func main() {
 	in, err := os.Open(inPath)
 	fail(err)
 
+	defer in.Close()
+
 	// hash the file
 	log.Print("hashing...")
 	h := sha1.New()
@@ -40,6 +42,18 @@ func main() {
 
 	log.Print("SHA1 of source: ", sha1Hex)
 
+	// check remote
+	head, err := http.Head(outURL)
+	fail(err)
+
+	if head.StatusCode == 200 {
+		remoteSHA1 := head.Header.Get("X-Content-SHA1")
+		if sha1Hex == remoteSHA1 {
+			log.Print("remote is already up-to-date")
+			return
+		}
+	}
+
 	// rewind
 	_, err = in.Seek(0, os.SEEK_SET)
 	fail(err)
diff --git a/modd.conf b/modd.conf
new file mode 100644
index 0000000..9996a60
--- /dev/null
+++ b/modd.conf
@@ -0,0 +1,4 @@
+**/*.go go.* {
+  prep: go test ./...
+  prep: go install ./cmd/...
+}