diff --git a/cmd/dbdiff/main.go b/cmd/dbdiff/main.go
new file mode 100644
index 0000000..6a39aef
--- /dev/null
+++ b/cmd/dbdiff/main.go
@@ -0,0 +1,84 @@
+// Copyright 2021 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"github.com/google/go-cmp/cmp"
+	"golang.org/x/vulndb/osv"
+)
+
+func loadDB(dbPath string) (osv.DBIndex, map[string][]osv.Entry, error) {
+	index := osv.DBIndex{}
+	dbMap := map[string][]osv.Entry{}
+
+	var loadDir func(string) error
+	loadDir = func(path string) error {
+		dir, err := ioutil.ReadDir(path)
+		if err != nil {
+			return err
+		}
+		for _, f := range dir {
+			fpath := filepath.Join(path, f.Name())
+			if f.IsDir() {
+				loadDir(fpath)
+				continue
+			}
+			content, err := ioutil.ReadFile(fpath)
+			if err != nil {
+				return err
+			}
+			if path == dbPath && f.Name() == "index.json" {
+				if err := json.Unmarshal(content, &index); err != nil {
+					return fmt.Errorf("unable to parse %q: %s", fpath, err)
+				}
+			} else {
+				var entries []osv.Entry
+				if err := json.Unmarshal(content, &entries); err != nil {
+					return fmt.Errorf("unable to parse %q: %s", fpath, err)
+				}
+				module := strings.TrimSuffix(strings.TrimPrefix(fpath, dbPath), filepath.Ext(fpath))
+				dbMap[module] = entries
+			}
+		}
+		return nil
+	}
+	if err := loadDir(dbPath); err != nil {
+		return nil, nil, err
+	}
+	return index, dbMap, nil
+}
+
+func main() {
+	if len(os.Args) != 3 {
+		fmt.Fprintln(os.Stderr, "usage: dbdiff db-a db-b")
+		os.Exit(1)
+	}
+	indexA, dbA, err := loadDB(os.Args[1])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "unable to load %q: %s\n", os.Args[1], err)
+		os.Exit(1)
+	}
+	indexB, dbB, err := loadDB(os.Args[2])
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "unable to load %q: %s\n", os.Args[2], err)
+		os.Exit(1)
+	}
+	indexDiff := cmp.Diff(indexA, indexB)
+	if indexDiff == "" {
+		indexDiff = "(no change)"
+	}
+	dbDiff := cmp.Diff(dbA, dbB)
+	if dbDiff == "" {
+		dbDiff = "(no change)"
+	}
+	fmt.Printf("# index\n%s\n\n# db\n%s\n", indexDiff, dbDiff)
+}