diff --git a/backend/Makefile b/backend/Makefile
index d3cbc27..5428056 100644
--- a/backend/Makefile
+++ b/backend/Makefile
@@ -18,7 +18,7 @@ GDB = 0
 ifeq ($(RELEASE),1)
 	CXXFLAGS += -O3
 else
-	CXXFLAGS += -g -Wno-unused
+	CXXFLAGS += -O0 -g -Wno-unused
 
 	ifeq ($(GDB),1)
 		CXXFLAGS += -ggdb
@@ -26,8 +26,17 @@ else
 endif
 
 ASAN = 0
+UBSAN = 0
 ifeq ($(ASAN),1)
-	CXXFLAGS += -fsanitize=address
+	ifeq ($(UBSAN),1)
+		CXXFLAGS += -fsanitize=address,undefined
+	else
+		CXXFLAGS += -fsanitize=address
+	endif
+else
+	ifeq ($(UBSAN),1)
+		CXXFLAGS += -fsanitize=undefined
+	endif
 endif
 
 MQTT_HOST=
diff --git a/backend/src/json.cpp b/backend/src/json.cpp
index efca07d..2694aa8 100644
--- a/backend/src/json.cpp
+++ b/backend/src/json.cpp
@@ -50,14 +50,14 @@ public:
             return Tok { TokTy::Eof, std::string_view(nullptr, 0), loc };
         }
         bool matched = false;
-        while (*i < m_len && std::strchr(" \t\r\n", m_text[*i]) != NULL) {
+        while (*i < m_len && std::strchr(" \t\r\n", m_text[*i]) != nullptr) {
             matched = true;
             step();
         }
         if (matched) {
             return next();
         }
-        if (strchr(",:[]{}0", m_text[*i]) != NULL) {
+        if (strchr(",:[]{}", m_text[*i]) != nullptr) {
             auto ty = (TokTy)m_text[*i];
             step();
             return tok(ty, loc);
@@ -69,7 +69,7 @@ public:
         if (matched) {
             return make_ident_tok(loc, i);
         }
-        if (m_text[*i] >= '1' && m_text[*i] <= '9') {
+        if (m_text[*i] == '-' || (m_text[*i] >= '0' && m_text[*i] <= '9')) {
             return make_number_tok(loc, i);
         }
         if (m_text[*i] == '\"') {
@@ -114,6 +114,7 @@ private:
 
     auto make_number_tok(Loc loc, size_t* i) -> Tok
     {
+        step();
         while (*i < m_len && m_text[*i] >= '0' && m_text[*i] <= '9') {
             step();
         }
@@ -220,12 +221,12 @@ public:
             CHECK(step());
             return val;
         } else if (*ty == TokTy::Int) {
-            int64_t value = std::strtol(m_tok.text.data(), NULL, 10);
+            int64_t value = std::strtol(m_tok.text.data(), nullptr, 10);
             auto val = std::make_unique<Value>(Type::I64, value);
             CHECK(step());
             return val;
         } else if (*ty == TokTy::Float) {
-            double value = std::strtod(m_tok.text.data(), NULL);
+            double value = std::strtod(m_tok.text.data(), nullptr);
             auto val = std::make_unique<Value>(Type::F64, value);
             CHECK(step());
             return val;
@@ -347,17 +348,17 @@ public:
         size_t idx = m_idx;
         size_t* i = &m_idx;
         if (*i >= m_text.size()) {
-            return tok(TokTy::Eof, idx);
+            return Tok { TokTy::Eof, std::string_view(nullptr, 0), idx };
         }
         bool matched = false;
-        while (*i < m_text.size() && strchr(" \t\r\n", m_text[*i]) != NULL) {
+        while (*i < m_text.size() && strchr(" \t\r\n", m_text[*i]) != nullptr) {
             matched = true;
             step();
         }
         if (matched) {
             return next();
         }
-        if (strchr(".[]0", m_text[*i]) != NULL) {
+        if (strchr(".[]0", m_text[*i]) != nullptr) {
             auto ty = static_cast<TokTy>(m_text[*i]);
             step();
             return tok(ty, idx);
@@ -407,7 +408,7 @@ private:
 
     auto tok(TokTy ty, size_t idx) -> Tok
     {
-        return { ty, std::string_view(&m_text[idx], this->m_idx - idx), idx };
+        return { ty, std::string_view(&m_text[idx], m_idx - idx), idx };
     }
 
     void step()
@@ -437,6 +438,7 @@ class Parser {
 public:
     Parser(std::string_view text)
         : m_tokenizer(text)
+        , m_tok(m_tokenizer.next().value())
     {
     }
 
@@ -522,7 +524,7 @@ auto resolve(Parser& parser, ValueT& node) -> Result<ValueT*, std::string>
         case PathSegTy::Idx: {
             if (!node.is(Type::Array))
                 return std::unexpected("expected array");
-            auto idx = strtoull(seg->tok.text.data(), NULL, 10);
+            auto idx = strtoull(seg->tok.text.data(), nullptr, 10);
             if (!node.has(idx))
                 return std::unexpected(std::format(
                     "array index {} out of bounds {}", idx, node.size()));
diff --git a/backend/src/main.cpp b/backend/src/main.cpp
index 4d06c0e..46265b6 100644
--- a/backend/src/main.cpp
+++ b/backend/src/main.cpp
@@ -7,6 +7,7 @@
 #include <iostream>
 #include <print>
 #include <span>
+#include <stdexcept>
 #include <string_view>
 #include <sys/select.h>
 #include <sys/socket.h>
@@ -36,10 +37,22 @@ int main(void)
     mqtt_client.subscribe("/skateboard/update", [&](std::string_view text) {
         //
         std::println("Skateboard: {}", text);
-        // auto parsed = mst::json::parse(text).value();
+        auto result = mst::json::parse(text);
 
-        // std::println(".acceleration[0]",
-        //     parsed->query(".acceleration[0]").value()->get_i64());
+        if (!result) {
+            std::println(stderr,
+                "error: {} at {}",
+                result.error().message,
+                result.error().loc.idx);
+            return;
+        }
+        try {
+            auto parsed = std::move(result.value());
+            std::println(".rotation = {}",
+                parsed->query(".rotation").value()->get_f64());
+        } catch (std::runtime_error& ex) {
+            std::println(stderr, "exception: {}", ex.what());
+        }
     });
 
     auto mqtt_thread = std::thread([&]() {
@@ -64,5 +77,7 @@ int main(void)
     {
         auto x = mgr.start();
     }
+
+    mqtt_thread.join();
     return 0;
 }
diff --git a/backend/tests/json.cpp b/backend/tests/json.cpp
index 4fd9d90..736a300 100644
--- a/backend/tests/json.cpp
+++ b/backend/tests/json.cpp
@@ -13,4 +13,12 @@ int main()
     ASSERT_EQ(**json::parse("3.14"), *json::Value::make_f64(3.14));
     ASSERT_EQ(**json::parse("\"hello world\""),
         *json::Value::make_string("hello world"));
+
+
+    {
+        auto object = *json::parse(R"({"rotation":-0.0123})");
+        auto query_result = object->query(std::string_view(".rotation"));
+        auto f64_value = query_result.value()->get_f64();
+        ASSERT_EQ(f64_value, -0.0123);
+    }
 }