diff --git a/runtime/example.slg b/runtime/example.slg
new file mode 100644
index 0000000..927726f
--- /dev/null
+++ b/runtime/example.slg
@@ -0,0 +1,14 @@
+fn add(a, b) {
+    + a b
+}
+
+let result = 0;
+let i = 0;
+loop {
+    if >= i 10 {
+        break;
+    }
+    result = add(result, 5);
+    i = + i 1;
+}
+
diff --git a/runtime/to_json.cpp b/runtime/to_json.cpp
new file mode 100644
index 0000000..09e35cb
--- /dev/null
+++ b/runtime/to_json.cpp
@@ -0,0 +1,41 @@
+#include "vm.hpp"
+#include <string>
+
+using namespace sliger;
+
+void FlameGraphBuilder::to_json(json::Writer& writer) const
+{
+    fg_node_to_json(writer, 0);
+}
+
+void FlameGraphBuilder::fg_node_to_json(
+    json::Writer& writer, size_t node_index) const
+{
+    const auto& node = this->nodes[node_index];
+    writer << "{\"fn\":" << std::to_string(node.fn)
+           << ",\"acc\":" << std::to_string(node.acc)
+           << ",\"parent\":" << std::to_string(node.parent)
+           << ",\"children:[\"";
+    auto first = true;
+    for (auto child_index : node.children) {
+        if (!first) {
+            writer << ",";
+        }
+        first = false;
+        fg_node_to_json(writer, child_index);
+    }
+    writer << "]}";
+}
+
+void CodeCoverageBuilder::to_json(json::Writer& writer) const
+{
+    writer << "[";
+    writer.add_comma_seperated(
+        this->entries, [&](json::Writer& writer, CCPosEntry entry) {
+            writer << "{\"index\":" << std::to_string(entry.pos.index)
+                   << ",\"line\":" << std::to_string(entry.pos.line)
+                   << ",\"col\":" << std::to_string(entry.pos.col)
+                   << ",\"covers\":" << std::to_string(entry.covers) << "}";
+        });
+    writer << "]";
+}