diff --git a/src/me/topchetoeu/jscript/mapping/LocationMap.java b/src/me/topchetoeu/jscript/mapping/LocationMap.java
new file mode 100644
index 0000000..f71a1c8
--- /dev/null
+++ b/src/me/topchetoeu/jscript/mapping/LocationMap.java
@@ -0,0 +1,16 @@
+package me.topchetoeu.jscript.mapping;
+
+import me.topchetoeu.jscript.Location;
+
+public interface LocationMap {
+    Location srcToDst(Location loc);
+    Location dstToSrc(Location loc);
+
+    default LocationMap chain(LocationMap next) {
+        var self = this;
+        return new LocationMap() {
+            public Location dstToSrc(Location loc) { return self.dstToSrc(next.dstToSrc(loc)); }
+            public Location srcToDst(Location loc) { return next.srcToDst(self.srcToDst(loc)); }
+        };
+    }
+}
diff --git a/src/me/topchetoeu/jscript/mapping/SourceMap.java b/src/me/topchetoeu/jscript/mapping/SourceMap.java
new file mode 100644
index 0000000..47fdc52
--- /dev/null
+++ b/src/me/topchetoeu/jscript/mapping/SourceMap.java
@@ -0,0 +1,67 @@
+package me.topchetoeu.jscript.mapping;
+
+import java.util.TreeMap;
+
+import me.topchetoeu.jscript.Filename;
+import me.topchetoeu.jscript.Location;
+import me.topchetoeu.jscript.json.JSON;
+
+public class SourceMap implements LocationMap {
+    private TreeMap<Location, Location> srcToDst = new TreeMap<>();
+    private TreeMap<Location, Location> dstToSrc = new TreeMap<>();
+
+    public Location srcToDst(Location loc) {
+        if (srcToDst.containsKey(loc)) return loc;
+
+        var tail = srcToDst.tailMap(loc);
+        if (tail.isEmpty()) return null;
+
+        var key = tail.firstKey();
+        if (key != null) return srcToDst.get(key);
+        else return null;
+    }
+    public Location dstToSrc(Location loc) {
+        if (dstToSrc.containsKey(loc)) return loc;
+
+        var tail = dstToSrc.tailMap(loc);
+        if (tail.isEmpty()) return null;
+
+        var key = tail.firstKey();
+        if (key != null) return dstToSrc.get(key);
+        else return null;
+    }
+
+    public static SourceMap parse(String raw) {
+        var res = new SourceMap();
+        var json = JSON.parse(null, raw).map();
+        if (json.number("version") != 3) throw new IllegalArgumentException("Source map version must be 3.");
+        var sources = json.list("sources").stream().map(v -> v.string()).toArray(String[]::new);
+        var dstFilename = Filename.parse(json.string("file"));
+        var mapping = VLQ.decodeMapping(json.string("mappings"));
+
+        var srcI = 0;
+        var srcRow = 0;
+        var srcCol = 0;
+
+        for (var dstRow = 0; dstRow < mapping.length; dstRow++) {
+            var dstCol = 0;
+
+            for (var rawSeg : mapping[dstRow]) {
+                dstCol += rawSeg.length > 0 ? rawSeg[0] : 0;
+                srcI += rawSeg.length > 1 ? rawSeg[1] : 0;
+                srcRow += rawSeg.length > 2 ? rawSeg[2] : 0;
+                srcCol += rawSeg.length > 3 ? rawSeg[3] : 0;
+
+                var src = new Location(srcRow + 1, srcCol + 1, Filename.parse(sources[srcI]));
+                var dst = new Location(dstRow + 1, dstCol + 1, dstFilename);
+
+                System.out.printf("%s -> %s\n", src, dst);
+
+                res.srcToDst.put(src, dst);
+                res.dstToSrc.put(dst, src);
+            }
+        }
+
+        return res;
+    }
+}