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diff --git a/src/main/java/com/seaofnodes/simple/GraphVisualizer.java b/src/main/java/com/seaofnodes/simple/GraphVisualizer.java
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+++ b/src/main/java/com/seaofnodes/simple/GraphVisualizer.java
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+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+
+import java.util.*;
+
+/**
+ * Simple visualizer that outputs GraphViz dot format.
+ * The dot output must be saved to a file and run manually via dot to generate the SVG output.
+ * Currently, this is done manually.
+ */
+public class GraphVisualizer {
+
+    public String generateDotOutput(Parser parser) {
+
+        // Since the graph has cycles, we need to create a flat list of all the
+        // nodes in the graph.
+        Collection<Node> all = findAll(parser);
+        StringBuilder sb = new StringBuilder();
+        sb.append("digraph chapter02 {\n");
+        sb.append("/*\n");
+        sb.append(parser.src());
+        sb.append("\n*/\n");
+
+        // To keep the Scopes below the graph and pointing up into the graph we
+        // need to group the Nodes in a subgraph cluster, and the scopes into a
+        // different subgraph cluster.  THEN we can draw edges between the
+        // scopes and nodes.  If we try to cross subgraph cluster borders while
+        // still making the subgraphs DOT gets confused.
+        sb.append("\trankdir=BT;\n"); // Force Nodes before Scopes
+
+        // Preserve node input order
+        sb.append("\tordering=\"in\";\n");
+
+        // Merge multiple edges hitting the same node.  Makes common shared
+        // nodes much prettier to look at.
+        sb.append("\tconcentrate=\"true\";\n");
+
+        // Just the Nodes first, in a cluster no edges
+        nodes(sb, all);
+
+        // Walk the Node edges
+        nodeEdges(sb, all);
+
+        sb.append("}\n");
+        return sb.toString();
+    }
+
+
+    private void nodes(StringBuilder sb, Collection<Node> all) {
+        // Just the Nodes first, in a cluster no edges
+        sb.append("\tsubgraph cluster_Nodes {\n"); // Magic "cluster_" in the subgraph name
+        for( Node n : all ) {
+            sb.append("\t\t").append(n.uniqueName()).append(" [ ");
+            String lab = n.glabel();
+            // control nodes have box shape
+            // other nodes are ellipses, i.e. default shape
+            if( n.isCFG() )
+                sb.append("shape=box style=filled fillcolor=yellow ");
+            sb.append("label=\"").append(lab).append("\" ");
+            sb.append("];\n");
+        }
+        sb.append("\t}\n");     // End Node cluster
+    }
+
+
+    // Walk the node edges
+    private void nodeEdges(StringBuilder sb, Collection<Node> all) {
+        // All them edge labels
+        sb.append("\tedge [ fontname=Helvetica, fontsize=8 ];\n");
+        for( Node n : all ) {
+            // In this chapter we do display the Constant->Start edge;
+            int i=0;
+            for( Node def : n._inputs ) {
+                if( def != null ) {
+                    // Most edges land here use->def
+                    sb.append('\t').append(n.uniqueName()).append(" -> ");
+                    sb.append(def.uniqueName());
+                    // Number edges, so we can see how they track
+                    sb.append("[taillabel=").append(i);
+                    if( n instanceof ConstantNode && def instanceof StartNode )
+                        sb.append(" style=dotted");
+                    // control edges are colored red
+                    else if( def.isCFG() )
+                        sb.append(" color=red");
+                    sb.append("];\n");
+                }
+                i++;
+            }
+        }
+    }
+
+    /**
+     * Finds all nodes in the graph.
+     */
+    private Collection<Node> findAll(Parser parser) {
+        final StartNode start = Parser.START;
+        final HashMap<Integer, Node> all = new HashMap<>();
+        for( Node n : start._outputs )
+            walk(all, n);
+        return all.values();
+    }
+
+    /**
+     * Walk a subgraph and populate distinct nodes in the all list.
+     */
+    private void walk(HashMap<Integer, Node> all, Node n) {
+        if (all.get(n._nid) != null) return; // Been there, done that
+        all.put(n._nid, n);
+        for (Node c : n._inputs)
+            if (c != null)
+                walk(all, c);
+        for (Node c : n._outputs)
+            if (c != null)
+                walk(all, c);
+    }
+}