diff --git a/build/fietsje/proto/shelf.proto b/build/fietsje/proto/shelf.proto
new file mode 100644
index 0000000..394e5f0
--- /dev/null
+++ b/build/fietsje/proto/shelf.proto
@@ -0,0 +1,33 @@
+// Copyright 2020 The Monogon Project Authors.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+package nexantic.build.fietsje;
+option go_package = "git.monogon.dev/source/nexantic.git/build/fietsje/proto";
+
+// The Shelf is a cache/lockfile of Fietsje dependencies. See //build/fietsje/shelf.go for more information.
+// This proto definition is used to generate text proto files. As such, repeated fields have singular names.
+
+message Shelf {
+    message Entry {
+        string import_path = 1;
+        string version = 2;
+        string bazel_name = 3;
+        string sum = 4;
+        string semver = 5;
+    }
+    repeated Entry entry = 1;
+}