diff --git a/.gitmodules b/.gitmodules
index e2c0733d..27ff39f0 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -10,6 +10,3 @@
 [submodule "third_party/loguru"]
 	path = third_party/loguru
 	url = https://github.com/emilk/loguru
-[submodule "third_party/msgpack-c"]
-	path = third_party/msgpack-c
-	url = https://github.com/msgpack/msgpack-c
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 36085bd0..f5183c7e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -135,8 +135,7 @@ target_include_directories(ccls PRIVATE
                            third_party/rapidjson/include
                            third_party/sparsepp
                            third_party/loguru
-                           third_party/doctest
-                           third_party/msgpack-c/include)
+                           third_party/doctest)
 
 ### Install
 
diff --git a/src/cache_manager.cc b/src/cache_manager.cc
index 19e7bb59..beb9186b 100644
--- a/src/cache_manager.cc
+++ b/src/cache_manager.cc
@@ -59,10 +59,10 @@ struct RealCacheManager : ICacheManager {
 
   std::string AppendSerializationFormat(const std::string& base) {
     switch (g_config->cacheFormat) {
+      case SerializeFormat::Binary:
+        return base + ".blob";
       case SerializeFormat::Json:
         return base + ".json";
-      case SerializeFormat::MessagePack:
-        return base + ".mpack";
     }
   }
 };
diff --git a/src/config.h b/src/config.h
index d4cfe163..c0d3774a 100644
--- a/src/config.h
+++ b/src/config.h
@@ -38,12 +38,10 @@ struct Config {
   // "json" generates `cacheDirectory/.../xxx.json` files which can be pretty
   // printed with jq.
   //
-  // "msgpack" uses a compact binary serialization format (the underlying wire
-  // format is [MessagePack](https://msgpack.org/index.html)) which typically
-  // takes only 60% of the corresponding JSON size, but is difficult to inspect.
-  // msgpack does not store map keys and you need to re-index whenever a struct
+  // "binary" uses a compact binary serialization format.
+  // It is not schema-aware and you need to re-index whenever a struct
   // member has changed.
-  SerializeFormat cacheFormat = SerializeFormat::MessagePack;
+  SerializeFormat cacheFormat = SerializeFormat::Binary;
   // Value to use for clang -resource-dir if not present in
   // compile_commands.json.
   //
diff --git a/src/file_consumer.cc b/src/file_consumer.cc
index a85c666f..796bb9f0 100644
--- a/src/file_consumer.cc
+++ b/src/file_consumer.cc
@@ -83,8 +83,8 @@ IndexFile* FileConsumer::TryConsumeFile(
   if (clang_getFileUniqueID(file, &file_id) != 0) {
     std::string file_name = FileName(file);
     if (!file_name.empty()) {
-      LOG_S(ERROR) << "Could not get unique file id for " << file_name
-                   << " when parsing " << parse_file_;
+      // LOG_S(ERROR) << "Could not get unique file id for " << file_name
+      // << " when parsing " << parse_file_;
     }
     return nullptr;
   }
diff --git a/src/serializer.cc b/src/serializer.cc
index 978e2550..2531c20e 100644
--- a/src/serializer.cc
+++ b/src/serializer.cc
@@ -1,8 +1,8 @@
 #include "serializer.h"
 
 #include "filesystem.hh"
+#include "serializers/binary.h"
 #include "serializers/json.h"
-#include "serializers/msgpack.h"
 
 #include "indexer.h"
 
@@ -15,12 +15,10 @@ bool gTestOutputMode = false;
 //// Elementary types
 
 void Reflect(Reader& visitor, uint8_t& value) {
-  if (!visitor.IsInt())
-    throw std::invalid_argument("uint8_t");
-  value = (uint8_t)visitor.GetInt();
+  value = visitor.GetUInt8();
 }
 void Reflect(Writer& visitor, uint8_t& value) {
-  visitor.Int(value);
+  visitor.UInt8(value);
 }
 
 void Reflect(Reader& visitor, short& value) {
@@ -51,12 +49,12 @@ void Reflect(Writer& visitor, int& value) {
 }
 
 void Reflect(Reader& visitor, unsigned& value) {
-  if (!visitor.IsUint64())
+  if (!visitor.IsUInt64())
     throw std::invalid_argument("unsigned");
-  value = visitor.GetUint32();
+  value = visitor.GetUInt32();
 }
 void Reflect(Writer& visitor, unsigned& value) {
-  visitor.Uint32(value);
+  visitor.UInt32(value);
 }
 
 void Reflect(Reader& visitor, long& value) {
@@ -69,12 +67,12 @@ void Reflect(Writer& visitor, long& value) {
 }
 
 void Reflect(Reader& visitor, unsigned long& value) {
-  if (!visitor.IsUint64())
+  if (!visitor.IsUInt64())
     throw std::invalid_argument("unsigned long");
-  value = (unsigned long)visitor.GetUint64();
+  value = (unsigned long)visitor.GetUInt64();
 }
 void Reflect(Writer& visitor, unsigned long& value) {
-  visitor.Uint64(value);
+  visitor.UInt64(value);
 }
 
 void Reflect(Reader& visitor, long long& value) {
@@ -87,12 +85,12 @@ void Reflect(Writer& visitor, long long& value) {
 }
 
 void Reflect(Reader& visitor, unsigned long long& value) {
-  if (!visitor.IsUint64())
+  if (!visitor.IsUInt64())
     throw std::invalid_argument("unsigned long long");
-  value = visitor.GetUint64();
+  value = visitor.GetUInt64();
 }
 void Reflect(Writer& visitor, unsigned long long& value) {
-  visitor.Uint64(value);
+  visitor.UInt64(value);
 }
 
 void Reflect(Reader& visitor, double& value) {
@@ -302,6 +300,7 @@ void Reflect(TVisitor& visitor, IndexFile& value) {
 }
 
 void Reflect(Reader& visitor, std::monostate&) {
+  assert(visitor.Format() == SerializeFormat::Json);
   visitor.GetNull();
 }
 
@@ -311,22 +310,31 @@ void Reflect(Writer& visitor, std::monostate&) {
 
 void Reflect(Reader& visitor, SerializeFormat& value) {
   std::string fmt = visitor.GetString();
-  value = fmt[0] == 'm' ? SerializeFormat::MessagePack : SerializeFormat::Json;
+  value = fmt[0] == 'b' ? SerializeFormat::Binary : SerializeFormat::Json;
 }
 
 void Reflect(Writer& visitor, SerializeFormat& value) {
   switch (value) {
+    case SerializeFormat::Binary:
+      visitor.String("binary");
+      break;
     case SerializeFormat::Json:
       visitor.String("json");
       break;
-    case SerializeFormat::MessagePack:
-      visitor.String("msgpack");
-      break;
   }
 }
 
 std::string Serialize(SerializeFormat format, IndexFile& file) {
   switch (format) {
+    case SerializeFormat::Binary: {
+      BinaryWriter writer;
+      int major = IndexFile::kMajorVersion;
+      int minor = IndexFile::kMinorVersion;
+      Reflect(writer, major);
+      Reflect(writer, minor);
+      Reflect(writer, file);
+      return writer.Take();
+    }
     case SerializeFormat::Json: {
       rapidjson::StringBuffer output;
       rapidjson::PrettyWriter<rapidjson::StringBuffer> writer(output);
@@ -343,17 +351,6 @@ std::string Serialize(SerializeFormat format, IndexFile& file) {
       Reflect(json_writer, file);
       return output.GetString();
     }
-    case SerializeFormat::MessagePack: {
-      msgpack::sbuffer buf;
-      msgpack::packer<msgpack::sbuffer> pk(&buf);
-      MessagePackWriter msgpack_writer(&pk);
-      uint64_t magic = IndexFile::kMajorVersion;
-      int version = IndexFile::kMinorVersion;
-      Reflect(msgpack_writer, magic);
-      Reflect(msgpack_writer, version);
-      Reflect(msgpack_writer, file);
-      return std::string(buf.data(), buf.size());
-    }
   }
   return "";
 }
@@ -369,6 +366,26 @@ std::unique_ptr<IndexFile> Deserialize(
 
   std::unique_ptr<IndexFile> file;
   switch (format) {
+    case SerializeFormat::Binary: {
+      try {
+        int major, minor;
+        if (serialized_index_content.size() < 8)
+          throw std::invalid_argument("Invalid");
+        BinaryReader reader(serialized_index_content);
+        Reflect(reader, major);
+        Reflect(reader, minor);
+        if (major != IndexFile::kMajorVersion ||
+            minor != IndexFile::kMinorVersion)
+          throw std::invalid_argument("Invalid version");
+        file = std::make_unique<IndexFile>(path, file_content);
+        Reflect(reader, *file);
+      } catch (std::invalid_argument& e) {
+        LOG_S(INFO) << "Failed to deserialize '" << path
+                    << "': " << e.what();
+        return nullptr;
+      }
+      break;
+    }
     case SerializeFormat::Json: {
       rapidjson::Document reader;
       if (gTestOutputMode || !expected_version) {
@@ -395,32 +412,6 @@ std::unique_ptr<IndexFile> Deserialize(
       }
       break;
     }
-
-    case SerializeFormat::MessagePack: {
-      try {
-        int major, minor;
-        if (serialized_index_content.size() < 8)
-          throw std::invalid_argument("Invalid");
-        msgpack::unpacker upk;
-        upk.reserve_buffer(serialized_index_content.size());
-        memcpy(upk.buffer(), serialized_index_content.data(),
-               serialized_index_content.size());
-        upk.buffer_consumed(serialized_index_content.size());
-        file = std::make_unique<IndexFile>(path, file_content);
-        MessagePackReader reader(&upk);
-        Reflect(reader, major);
-        Reflect(reader, minor);
-        if (major != IndexFile::kMajorVersion ||
-            minor != IndexFile::kMinorVersion)
-          throw std::invalid_argument("Invalid version");
-        Reflect(reader, *file);
-      } catch (std::invalid_argument& e) {
-        LOG_S(INFO) << "Failed to deserialize msgpack '" << path
-                    << "': " << e.what();
-        return nullptr;
-      }
-      break;
-    }
   }
 
   // Restore non-serialized state.
diff --git a/src/serializer.h b/src/serializer.h
index d7a6ed9e..edb35e1f 100644
--- a/src/serializer.h
+++ b/src/serializer.h
@@ -16,7 +16,7 @@
 #include <variant>
 #include <vector>
 
-enum class SerializeFormat { Json, MessagePack };
+enum class SerializeFormat { Binary, Json };
 
 class Reader {
  public:
@@ -27,16 +27,17 @@ class Reader {
   virtual bool IsNull() = 0;
   virtual bool IsInt() = 0;
   virtual bool IsInt64() = 0;
-  virtual bool IsUint64() = 0;
+  virtual bool IsUInt64() = 0;
   virtual bool IsDouble() = 0;
   virtual bool IsString() = 0;
 
   virtual void GetNull() = 0;
   virtual bool GetBool() = 0;
+  virtual uint8_t GetUInt8() = 0;
   virtual int GetInt() = 0;
-  virtual uint32_t GetUint32() = 0;
+  virtual uint32_t GetUInt32() = 0;
   virtual int64_t GetInt64() = 0;
-  virtual uint64_t GetUint64() = 0;
+  virtual uint64_t GetUInt64() = 0;
   virtual double GetDouble() = 0;
   virtual std::string GetString() = 0;
 
@@ -55,9 +56,10 @@ class Writer {
   virtual void Null() = 0;
   virtual void Bool(bool x) = 0;
   virtual void Int(int x) = 0;
-  virtual void Uint32(uint32_t x) = 0;
   virtual void Int64(int64_t x) = 0;
-  virtual void Uint64(uint64_t x) = 0;
+  virtual void UInt8(uint8_t x) = 0;
+  virtual void UInt32(uint32_t x) = 0;
+  virtual void UInt64(uint64_t x) = 0;
   virtual void Double(double x) = 0;
   virtual void String(const char* x) = 0;
   virtual void String(const char* x, size_t len) = 0;
@@ -192,9 +194,11 @@ void Reflect(Reader& visitor, std::optional<T>& value) {
 }
 template <typename T>
 void Reflect(Writer& visitor, std::optional<T>& value) {
-  if (value)
+  if (value) {
+    if (visitor.Format() != SerializeFormat::Json)
+      visitor.UInt8(1);
     Reflect(visitor, *value);
-  else
+  } else
     visitor.Null();
 }
 
@@ -211,9 +215,11 @@ void Reflect(Reader& visitor, Maybe<T>& value) {
 }
 template <typename T>
 void Reflect(Writer& visitor, Maybe<T>& value) {
-  if (value)
+  if (value) {
+    if (visitor.Format() != SerializeFormat::Json)
+      visitor.UInt8(1);
     Reflect(visitor, *value);
-  else
+  } else
     visitor.Null();
 }
 
diff --git a/src/serializers/binary.h b/src/serializers/binary.h
new file mode 100644
index 00000000..ad6d64fe
--- /dev/null
+++ b/src/serializers/binary.h
@@ -0,0 +1,131 @@
+#pragma once
+
+#include "serializer.h"
+
+#include <assert.h>
+
+class BinaryReader : public Reader {
+  const char* p_;
+
+  template <typename T>
+  T Get() {
+    auto ret = *reinterpret_cast<const T*>(p_);
+    p_ += sizeof(T);
+    return ret;
+  }
+
+  uint64_t VarUInt() {
+    auto x = *reinterpret_cast<const uint8_t*>(p_++);
+    if (x < 253)
+      return x;
+    if (x == 253)
+      return Get<uint16_t>();
+    if (x == 254)
+      return Get<uint32_t>();
+    return Get<uint64_t>();
+  }
+  int64_t VarInt() {
+    uint64_t x = VarUInt();
+    return int64_t(x >> 1 ^ -(x & 1));
+  }
+
+ public:
+  BinaryReader(std::string_view buf) : p_(buf.data()) {}
+  SerializeFormat Format() const override {
+    return SerializeFormat::Binary;
+  }
+
+  bool IsBool() override { return true; }
+  // Abuse how the function is called in serializer.h
+  bool IsNull() override { return !*p_++; }
+  bool IsInt() override { return true; }
+  bool IsInt64() override {return true;}
+  bool IsUInt64() override {return true;}
+  bool IsDouble() override {return true;};
+  bool IsString() override {return true;}
+
+  void GetNull() override {}
+  bool GetBool() override { return Get<bool>(); }
+  int GetInt() override { return VarInt(); }
+  int64_t GetInt64() override { return VarInt(); }
+  uint8_t GetUInt8() override { return Get<uint8_t>(); }
+  uint32_t GetUInt32() override { return VarUInt(); }
+  uint64_t GetUInt64() override { return VarUInt(); }
+  double GetDouble() override { return Get<double>(); }
+  std::string GetString() override {
+    if (auto n = VarUInt()) {
+      std::string ret(p_, n);
+      p_ += n;
+      return ret;
+    }
+    return "";
+  }
+
+  bool HasMember(const char* x) override { return true; }
+  std::unique_ptr<Reader> operator[](const char* x) override { return {}; }
+
+  void IterArray(std::function<void(Reader&)> fn) override {
+    for (auto n = VarUInt(); n; n--)
+      fn(*this);
+  }
+
+  void DoMember(const char*, std::function<void(Reader&)> fn) override {
+    fn(*this);
+  }
+};
+
+class BinaryWriter : public Writer {
+  std::string buf_;
+
+  template <typename T>
+  void Pack(T x) {
+    auto i = buf_.size();
+    buf_.resize(i + sizeof(x));
+    *reinterpret_cast<T*>(buf_.data() + i) = x;
+  }
+
+  void VarUInt(uint64_t n) {
+    if (n < 253)
+      Pack<uint8_t>(n);
+    else if (n < 65536) {
+      Pack<uint8_t>(253);
+      Pack<uint16_t>(n);
+    } else if (n < 4294967296) {
+      Pack<uint8_t>(254);
+      Pack<uint32_t>(n);
+    } else {
+      Pack<uint8_t>(255);
+      Pack<uint64_t>(n);
+    }
+  }
+  void VarInt(int64_t n) {
+    VarUInt(uint64_t(n) << 1 ^ n >> 63);
+  }
+
+ public:
+  SerializeFormat Format() const override {
+    return SerializeFormat::Binary;
+  }
+  std::string Take() { return std::move(buf_); }
+
+  void Null() override { Pack(uint8_t(0)); }
+  void Bool(bool x) override { Pack(x); }
+  void Int(int x) override { VarInt(x); }
+  void Int64(int64_t x) override { VarInt(x); }
+  void UInt8(uint8_t x) override { Pack(x); }
+  void UInt32(uint32_t x) override { VarUInt(x); }
+  void UInt64(uint64_t x) override { VarUInt(x); }
+  void Double(double x) override { Pack(x); }
+  void String(const char* x) override { String(x, strlen(x)); }
+  void String(const char* x, size_t len) override {
+    VarUInt(len);
+    auto i = buf_.size();
+    buf_.resize(i + len);
+    memcpy(buf_.data() + i, x, len);
+  }
+  void StartArray(size_t n) override { VarUInt(n); }
+  void EndArray() override {}
+  void StartObject() override {}
+  void EndObject() override {}
+  void Key(const char* name) override {}
+};
diff --git a/src/serializers/json.h b/src/serializers/json.h
index aa9d5f0f..d4f25f48 100644
--- a/src/serializers/json.h
+++ b/src/serializers/json.h
@@ -17,16 +17,17 @@ class JsonReader : public Reader {
   bool IsNull() override { return m_->IsNull(); }
   bool IsInt() override { return m_->IsInt(); }
   bool IsInt64() override { return m_->IsInt64(); }
-  bool IsUint64() override { return m_->IsUint64(); }
+  bool IsUInt64() override { return m_->IsUint64(); }
   bool IsDouble() override { return m_->IsDouble(); }
   bool IsString() override { return m_->IsString(); }
 
   void GetNull() override {}
   bool GetBool() override { return m_->GetBool(); }
   int GetInt() override { return m_->GetInt(); }
-  uint32_t GetUint32() override { return uint32_t(m_->GetUint64()); }
   int64_t GetInt64() override { return m_->GetInt64(); }
-  uint64_t GetUint64() override { return m_->GetUint64(); }
+  uint8_t GetUInt8() override { return uint8_t(m_->GetInt()); }
+  uint32_t GetUInt32() override { return uint32_t(m_->GetUint64()); }
+  uint64_t GetUInt64() override { return m_->GetUint64(); }
   double GetDouble() override { return m_->GetDouble(); }
   std::string GetString() override { return m_->GetString(); }
 
@@ -83,9 +84,10 @@ class JsonWriter : public Writer {
   void Null() override { m_->Null(); }
   void Bool(bool x) override { m_->Bool(x); }
   void Int(int x) override { m_->Int(x); }
-  void Uint32(uint32_t x) override { m_->Uint64(x); }
   void Int64(int64_t x) override { m_->Int64(x); }
-  void Uint64(uint64_t x) override { m_->Uint64(x); }
+  void UInt8(uint8_t x) override { m_->Int(x); }
+  void UInt32(uint32_t x) override { m_->Uint64(x); }
+  void UInt64(uint64_t x) override { m_->Uint64(x); }
   void Double(double x) override { m_->Double(x); }
   void String(const char* x) override { m_->String(x); }
   void String(const char* x, size_t len) override { m_->String(x, len); }
diff --git a/src/serializers/msgpack.h b/src/serializers/msgpack.h
deleted file mode 100644
index 83ea5983..00000000
--- a/src/serializers/msgpack.h
+++ /dev/null
@@ -1,84 +0,0 @@
-#pragma once
-
-#include "serializer.h"
-
-#include <msgpack.hpp>
-
-class MessagePackReader : public Reader {
-  msgpack::unpacker* pk_;
-  msgpack::object_handle oh_;
-
-  template <typename T>
-  T Get() {
-    T ret = oh_.get().as<T>();
-    pk_->next(oh_);
-    return ret;
-  }
-
- public:
-  MessagePackReader(msgpack::unpacker* pk) : pk_(pk) { pk->next(oh_); }
-  SerializeFormat Format() const override {
-    return SerializeFormat::MessagePack;
-  }
-
-  bool IsBool() override { return oh_.get().type == msgpack::type::BOOLEAN; }
-  bool IsNull() override { return oh_.get().is_nil(); }
-  bool IsInt() override {
-    return oh_.get().type == msgpack::type::POSITIVE_INTEGER ||
-           oh_.get().type == msgpack::type::NEGATIVE_INTEGER;
-  }
-  bool IsInt64() override { return IsInt(); }
-  bool IsUint64() override { return IsInt(); }
-  bool IsDouble() override { return oh_.get().type == msgpack::type::FLOAT64; };
-  bool IsString() override { return oh_.get().type == msgpack::type::STR; }
-
-  void GetNull() override { pk_->next(oh_); }
-  bool GetBool() override { return Get<bool>(); }
-  int GetInt() override { return Get<int>(); }
-  uint32_t GetUint32() override { return Get<uint32_t>(); }
-  int64_t GetInt64() override { return Get<int64_t>(); }
-  uint64_t GetUint64() override { return Get<uint64_t>(); }
-  double GetDouble() override { return Get<double>(); }
-  std::string GetString() override { return Get<std::string>(); }
-
-  bool HasMember(const char* x) override { return true; }
-  std::unique_ptr<Reader> operator[](const char* x) override { return {}; }
-
-  void IterArray(std::function<void(Reader&)> fn) override {
-    size_t n = Get<size_t>();
-    for (size_t i = 0; i < n; i++)
-      fn(*this);
-  }
-
-  void DoMember(const char*, std::function<void(Reader&)> fn) override {
-    fn(*this);
-  }
-};
-
-class MessagePackWriter : public Writer {
-  msgpack::packer<msgpack::sbuffer>* m_;
-
- public:
-  MessagePackWriter(msgpack::packer<msgpack::sbuffer>* m) : m_(m) {}
-  SerializeFormat Format() const override {
-    return SerializeFormat::MessagePack;
-  }
-
-  void Null() override { m_->pack_nil(); }
-  void Bool(bool x) override { m_->pack(x); }
-  void Int(int x) override { m_->pack(x); }
-  void Uint32(uint32_t x) override { m_->pack(x); }
-  void Int64(int64_t x) override { m_->pack(x); }
-  void Uint64(uint64_t x) override { m_->pack(x); }
-  void Double(double x) override { m_->pack(x); }
-  void String(const char* x) override { m_->pack(x); }
-  // TODO Remove std::string
-  void String(const char* x, size_t len) override {
-    m_->pack(std::string(x, len));
-  }
-  void StartArray(size_t n) override { m_->pack(n); }
-  void EndArray() override {}
-  void StartObject() override {}
-  void EndObject() override {}
-  void Key(const char* name) override {}
-};
diff --git a/third_party/msgpack-c b/third_party/msgpack-c
deleted file mode 160000
index 208595b2..00000000
--- a/third_party/msgpack-c
+++ /dev/null
@@ -1 +0,0 @@
-Subproject commit 208595b2620cf6260ce3d6d4cf8543f13b206449