diff --git a/src/main/java/net/rsxm/lib/Rsxm.java b/src/main/java/net/rsxm/lib/Rsxm.java
new file mode 100644
index 0000000..336ca8a
--- /dev/null
+++ b/src/main/java/net/rsxm/lib/Rsxm.java
@@ -0,0 +1,24 @@
+package net.rsxm.lib;
+
+/**
+ * What this library is and which version of it a mod was built against.
+ *
+ * A mod prints this in its log on startup, so a mismatch between the library a
+ * mod was compiled against and the one sitting in libs\ is visible immediately
+ * instead of turning into a NoSuchMethodError in the middle of a session.
+ */
+public final class Rsxm {
+
+    /** Bump when the public surface changes in a way that breaks compilation. */
+    public static final String VERSION = "0.1.0";
+
+    /** Where mods are expected to find this library. */
+    public static final String LIB_DIR = "libs";
+
+    private Rsxm() {
+    }
+
+    public static String describe() {
+        return "rsxm-lib " + VERSION;
+    }
+}