diff --git a/java/com/google/gerrit/util/cli/ApiProtocolBufferGenerator.java b/java/com/google/gerrit/util/cli/ApiProtocolBufferGenerator.java
new file mode 100644
index 0000000..27e4b17
--- /dev/null
+++ b/java/com/google/gerrit/util/cli/ApiProtocolBufferGenerator.java
@@ -0,0 +1,176 @@
+// Copyright (C) 2023 The Android Open Source Project
+//
+// 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.
+
+package com.google.gerrit.util.cli;
+
+import com.google.common.base.CaseFormat;
+import com.google.common.reflect.ClassPath;
+import java.lang.reflect.Field;
+import java.lang.reflect.ParameterizedType;
+import java.sql.Timestamp;
+import java.util.List;
+import java.util.Map;
+import java.util.Optional;
+
+/**
+ * Utility to generate Protocol Buffers (*.proto) files from existing POJO API types.
+ *
+ * <p>Usage:
+ *
+ * <ul>
+ *   <li>Print proto representation of all API objects: {@code bazelisk run
+ *       java/com/google/gerrit/util/cli:protogen}
+ * </ul>
+ */
+public class ApiProtocolBufferGenerator {
+  private static String NOTICE =
+      "// Copyright (C) 2023 The Android Open Source Project\n"
+          + "//\n"
+          + "// Licensed under the Apache License, Version 2.0 (the \"License\");\n"
+          + "// you may not use this file except in compliance with the License.\n"
+          + "// You may obtain a copy of the License at\n"
+          + "//\n"
+          + "// http://www.apache.org/licenses/LICENSE-2.0\n"
+          + "//\n"
+          + "// Unless required by applicable law or agreed to in writing, software\n"
+          + "// distributed under the License is distributed on an \"AS IS\" BASIS,\n"
+          + "// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.\n"
+          + "// See the License for the specific language governing permissions and\n"
+          + "// limitations under the License.";
+
+  private static String PACKAGE = "com.google.gerrit.extensions.common";
+
+  public static void main(String[] args) {
+    try {
+      ClassPath.from(ClassLoader.getSystemClassLoader()).getAllClasses().stream()
+          .filter(c -> c.getPackageName().equalsIgnoreCase(PACKAGE))
+          .filter(c -> c.getName().endsWith("Input") || c.getName().endsWith("Info"))
+          .map(clazz -> clazz.load())
+          .forEach(ApiProtocolBufferGenerator::exportSingleClass);
+    } catch (Exception e) {
+      System.err.println(e);
+    }
+  }
+
+  private static void exportSingleClass(Class<?> clazz) {
+    StringBuilder proto = new StringBuilder(NOTICE);
+    proto.append("\n\nsyntax = \"proto3\";");
+    proto.append("\n\npackage gerrit.api;");
+    proto.append("\n\noption java_package = \"" + PACKAGE + "\";");
+
+    int fieldNumber = 1;
+
+    proto.append("\n\n\nmessage " + clazz.getSimpleName() + " {\n");
+
+    for (Field f : clazz.getFields()) {
+      Class<?> type = f.getType();
+
+      if (type.isAssignableFrom(List.class)) {
+        ParameterizedType list = (ParameterizedType) f.getGenericType();
+        Class<?> genericType = (Class<?>) list.getActualTypeArguments()[0];
+        String protoType =
+            protoType(genericType)
+                .orElseThrow(() -> new IllegalStateException("unknown type: " + genericType));
+        proto.append(
+            String.format(
+                "repeated %s %s = %d;\n", protoType, protoName(f.getName()), fieldNumber));
+      } else if (type.isAssignableFrom(Map.class)) {
+        ParameterizedType map = (ParameterizedType) f.getGenericType();
+        Class<?> key = (Class<?>) map.getActualTypeArguments()[0];
+        if (map.getActualTypeArguments()[1] instanceof ParameterizedType) {
+          // TODO: This is list multimap which proto doesn't support. Move to
+          // it's own types.
+          proto.append(
+              "reserved "
+                  + fieldNumber
+                  + "; // TODO(hiesel): Add support for map<?,repeated <?>>\n");
+        } else {
+          Class<?> value = (Class<?>) map.getActualTypeArguments()[1];
+          String keyProtoType =
+              protoType(key).orElseThrow(() -> new IllegalStateException("unknown type: " + key));
+          String valueProtoType =
+              protoType(value)
+                  .orElseThrow(() -> new IllegalStateException("unknown type: " + value));
+          proto.append(
+              String.format(
+                  "map<%s,%s> %s = %d;\n",
+                  keyProtoType, valueProtoType, protoName(f.getName()), fieldNumber));
+        }
+      } else if (protoType(type).isPresent()) {
+        proto.append(
+            String.format(
+                "%s %s = %d;\n", protoType(type).get(), protoName(f.getName()), fieldNumber));
+      } else {
+        proto.append(
+            "reserved "
+                + fieldNumber
+                + "; // TODO(hiesel): Add support for "
+                + type.getName()
+                + "\n");
+      }
+      fieldNumber++;
+    }
+    proto.append("}");
+
+    System.out.println(proto);
+  }
+
+  private static Optional<String> protoType(Class<?> type) {
+    if (isInt(type)) {
+      return Optional.of("int32");
+    } else if (isLong(type)) {
+      return Optional.of("int64");
+    } else if (isChar(type)) {
+      return Optional.of("string");
+    } else if (isShort(type)) {
+      return Optional.of("int32");
+    } else if (isShort(type)) {
+      return Optional.of("int32");
+    } else if (isBoolean(type)) {
+      return Optional.of("bool");
+    } else if (type.isAssignableFrom(String.class)) {
+      return Optional.of("string");
+    } else if (type.isAssignableFrom(Timestamp.class)) {
+      // See https://gerrit-review.googlesource.com/Documentation/rest-api.html#timestamp
+      return Optional.of("string");
+    } else if (type.getPackageName().startsWith("com.google.gerrit.extensions")) {
+      return Optional.of("gerrit.api." + type.getSimpleName());
+    }
+    return Optional.empty();
+  }
+
+  private static boolean isInt(Class<?> type) {
+    return type.isAssignableFrom(Integer.class) || type.isAssignableFrom(int.class);
+  }
+
+  private static boolean isLong(Class<?> type) {
+    return type.isAssignableFrom(Long.class) || type.isAssignableFrom(long.class);
+  }
+
+  private static boolean isChar(Class<?> type) {
+    return type.isAssignableFrom(Character.class) || type.isAssignableFrom(char.class);
+  }
+
+  private static boolean isShort(Class<?> type) {
+    return type.isAssignableFrom(Short.class) || type.isAssignableFrom(short.class);
+  }
+
+  private static boolean isBoolean(Class<?> type) {
+    return type.isAssignableFrom(Boolean.class) || type.isAssignableFrom(boolean.class);
+  }
+
+  private static String protoName(String name) {
+    return CaseFormat.LOWER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, name);
+  }
+}
diff --git a/java/com/google/gerrit/util/cli/BUILD b/java/com/google/gerrit/util/cli/BUILD
index ebcc67e..b464f32 100644
--- a/java/com/google/gerrit/util/cli/BUILD
+++ b/java/com/google/gerrit/util/cli/BUILD
@@ -2,7 +2,10 @@
 
 java_library(
     name = "cli",
-    srcs = glob(["**/*.java"]),
+    srcs = glob(
+        ["**/*.java"],
+        exclude = ["ApiProtocolBufferGenerator.java"],
+    ),
     visibility = ["//visibility:public"],
     deps = [
         "//java/com/google/gerrit/common:annotations",
@@ -14,3 +17,15 @@
         "//lib/guice:guice-assistedinject",
     ],
 )
+
+# Util to generate *.proto files from *Info and *Input objects
+java_binary(
+    name = "protogen",
+    srcs = ["ApiProtocolBufferGenerator.java"],
+    main_class = "com.google.gerrit.util.cli.ApiProtocolBufferGenerator",
+    deps = [
+        "//java/com/google/gerrit/extensions:api",
+        "//lib:guava",
+        "//lib:protobuf",
+    ],
+)