diff --git a/src/main/java/com/threerings/getdown/tools/JarDiffCodes.java b/src/main/java/com/threerings/getdown/tools/JarDiffCodes.java
new file mode 100644
index 0000000..a391b2d
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+++ b/src/main/java/com/threerings/getdown/tools/JarDiffCodes.java
@@ -0,0 +1,43 @@
+//
+// $Id$
+//
+// Getdown - application installer, patcher and launcher
+// Copyright (C) 2004-2010 Three Rings Design, Inc.
+//
+// Redistribution and use in source and binary forms, with or without modification, are permitted
+// provided that the following conditions are met:
+// 
+// 1. Redistributions of source code must retain the above copyright notice, this list of
+//    conditions and the following disclaimer.
+// 2. Redistributions in binary form must reproduce the above copyright notice, this list of
+//    conditions and the following disclaimer in the documentation and/or other materials provided
+//    with the distribution.
+// 
+// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES,
+// INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+// PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT,
+// INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED
+// TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+// INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+// LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+// SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+package com.threerings.getdown.tools;
+
+/**
+ * Constants shared by {@link JarDiff} and {@link JarDiffPatcher}.
+ */
+public interface JarDiffCodes
+{
+    /** The name of the jardiff control file. */
+    String INDEX_NAME = "META-INF/INDEX.JD";
+
+    /** The version header used in the control file. */
+    String VERSION_HEADER = "version 1.0";
+
+    /** A jardiff command to remove an entry. */
+    String REMOVE_COMMAND = "remove";
+
+    /** A jardiff command to move an entry. */
+    String MOVE_COMMAND = "move";
+}