https://github.com/JDevlieghere updated 
https://github.com/llvm/llvm-project/pull/143628

>From 0db4451b1413f16443a7105f4aaa59597b166955 Mon Sep 17 00:00:00 2001
From: Jonas Devlieghere <jo...@devlieghere.com>
Date: Wed, 4 Jun 2025 23:56:57 -0700
Subject: [PATCH] [lldb] Add MCP support to LLDB (PoC)

---
 lldb/include/lldb/MCP/MCPError.h              |  33 +++
 lldb/include/lldb/MCP/Protocol.h              | 131 +++++++++
 lldb/include/lldb/MCP/Server.h                |  67 +++++
 lldb/include/lldb/MCP/Tool.h                  |  45 ++++
 lldb/source/CMakeLists.txt                    |   1 +
 lldb/source/Commands/CMakeLists.txt           |   2 +
 lldb/source/Commands/CommandObjectMCP.cpp     | 162 +++++++++++
 lldb/source/Commands/CommandObjectMCP.h       |  24 ++
 .../source/Interpreter/CommandInterpreter.cpp |   2 +
 lldb/source/MCP/CMakeLists.txt                |  13 +
 lldb/source/MCP/MCPError.cpp                  |  31 +++
 lldb/source/MCP/Protocol.cpp                  | 180 +++++++++++++
 lldb/source/MCP/Server.cpp                    | 251 ++++++++++++++++++
 lldb/source/MCP/Tool.cpp                      |  28 ++
 14 files changed, 970 insertions(+)
 create mode 100644 lldb/include/lldb/MCP/MCPError.h
 create mode 100644 lldb/include/lldb/MCP/Protocol.h
 create mode 100644 lldb/include/lldb/MCP/Server.h
 create mode 100644 lldb/include/lldb/MCP/Tool.h
 create mode 100644 lldb/source/Commands/CommandObjectMCP.cpp
 create mode 100644 lldb/source/Commands/CommandObjectMCP.h
 create mode 100644 lldb/source/MCP/CMakeLists.txt
 create mode 100644 lldb/source/MCP/MCPError.cpp
 create mode 100644 lldb/source/MCP/Protocol.cpp
 create mode 100644 lldb/source/MCP/Server.cpp
 create mode 100644 lldb/source/MCP/Tool.cpp

diff --git a/lldb/include/lldb/MCP/MCPError.h b/lldb/include/lldb/MCP/MCPError.h
new file mode 100644
index 0000000000000..2a76a7b087e20
--- /dev/null
+++ b/lldb/include/lldb/MCP/MCPError.h
@@ -0,0 +1,33 @@
+//===-- MCPError.h 
--------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "Protocol.h"
+#include "llvm/Support/Error.h"
+#include <string>
+
+namespace lldb_private::mcp {
+
+class MCPError : public llvm::ErrorInfo<MCPError> {
+public:
+  static char ID;
+
+  MCPError(std::string message, int64_t error_code);
+
+  void log(llvm::raw_ostream &OS) const override;
+  std::error_code convertToErrorCode() const override;
+
+  const std::string &getMessage() const { return m_message; }
+
+  protocol::Error toProtcolError() const;
+
+private:
+  std::string m_message;
+  int64_t m_error_code;
+};
+
+} // namespace lldb_private::mcp
diff --git a/lldb/include/lldb/MCP/Protocol.h b/lldb/include/lldb/MCP/Protocol.h
new file mode 100644
index 0000000000000..e661c3f7643af
--- /dev/null
+++ b/lldb/include/lldb/MCP/Protocol.h
@@ -0,0 +1,131 @@
+//===- Protocol.h 
---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_TOOLS_LLDB_MCP_PROTOCOL_H
+#define LLDB_TOOLS_LLDB_MCP_PROTOCOL_H
+
+#include "llvm/Support/JSON.h"
+#include <optional>
+#include <string>
+
+namespace lldb_private::mcp::protocol {
+
+static llvm::StringLiteral kProtocolVersion = "2025-03-26";
+
+struct Request {
+  uint64_t id = 0;
+  std::string method;
+  std::optional<llvm::json::Value> params;
+};
+
+llvm::json::Value toJSON(const Request &);
+bool fromJSON(const llvm::json::Value &, Request &, llvm::json::Path);
+
+struct Error {
+  int64_t code = 0;
+  std::string message;
+  std::optional<std::string> data;
+};
+
+llvm::json::Value toJSON(const Error &);
+bool fromJSON(const llvm::json::Value &, Error &, llvm::json::Path);
+
+struct ProtocolError {
+  uint64_t id = 0;
+  Error error;
+};
+
+llvm::json::Value toJSON(const ProtocolError &);
+bool fromJSON(const llvm::json::Value &, ProtocolError &, llvm::json::Path);
+
+struct Response {
+  uint64_t id = 0;
+  std::optional<llvm::json::Value> result;
+  std::optional<Error> error;
+};
+
+llvm::json::Value toJSON(const Response &);
+bool fromJSON(const llvm::json::Value &, Response &, llvm::json::Path);
+
+struct Notification {
+  std::string method;
+  std::optional<llvm::json::Value> params;
+};
+
+llvm::json::Value toJSON(const Notification &);
+bool fromJSON(const llvm::json::Value &, Notification &, llvm::json::Path);
+
+struct ToolCapability {
+  bool listChanged = false;
+};
+
+llvm::json::Value toJSON(const ToolCapability &);
+bool fromJSON(const llvm::json::Value &, ToolCapability &, llvm::json::Path);
+
+struct Capabilities {
+  ToolCapability tools;
+};
+
+llvm::json::Value toJSON(const Capabilities &);
+bool fromJSON(const llvm::json::Value &, Capabilities &, llvm::json::Path);
+
+struct TextContent {
+  std::string text;
+};
+
+llvm::json::Value toJSON(const TextContent &);
+bool fromJSON(const llvm::json::Value &, TextContent &, llvm::json::Path);
+
+struct TextResult {
+  std::vector<TextContent> content;
+  bool isError = false;
+};
+
+llvm::json::Value toJSON(const TextResult &);
+bool fromJSON(const llvm::json::Value &, TextResult &, llvm::json::Path);
+
+struct ToolAnnotations {
+  // Human-readable title for the tool.
+  std::optional<std::string> title;
+
+  /// If true, the tool does not modify its environment.
+  std::optional<bool> readOnlyHint;
+
+  /// If true, the tool may perform destructive updates.
+  std::optional<bool> destructiveHint;
+
+  /// If true, repeated calls with same args have no additional effect.
+  std::optional<bool> idempotentHint;
+
+  /// If true, tool interacts with external entities.
+  std::optional<bool> openWorldHint;
+};
+
+llvm::json::Value toJSON(const ToolAnnotations &);
+bool fromJSON(const llvm::json::Value &, ToolAnnotations &, llvm::json::Path);
+
+struct ToolDefinition {
+  /// Unique identifier for the tool.
+  std::string name;
+
+  /// Human-readable description.
+  std::optional<std::string> description;
+
+  // JSON Schema for the tool's parameters.
+  std::optional<llvm::json::Value> inputSchema;
+
+  // Optional hints about tool behavior.
+  std::optional<ToolAnnotations> annotations;
+};
+
+llvm::json::Value toJSON(const ToolDefinition &);
+bool fromJSON(const llvm::json::Value &, ToolDefinition &, llvm::json::Path);
+
+} // namespace lldb_private::mcp::protocol
+
+#endif
diff --git a/lldb/include/lldb/MCP/Server.h b/lldb/include/lldb/MCP/Server.h
new file mode 100644
index 0000000000000..2f65e1ddb6fb7
--- /dev/null
+++ b/lldb/include/lldb/MCP/Server.h
@@ -0,0 +1,67 @@
+//===- Server.h 
-----------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_TOOLS_LLDB_MCP_SERVER_H
+#define LLDB_TOOLS_LLDB_MCP_SERVER_H
+
+#include "Protocol.h"
+#include "Tool.h"
+#include "lldb/Host/JSONTransport.h"
+#include "lldb/Host/MainLoop.h"
+#include "lldb/Host/Socket.h"
+#include "llvm/ADT/StringMap.h"
+#include <string>
+#include <thread>
+
+namespace lldb_private::mcp {
+
+class Server {
+public:
+  Server(std::string name, std::string version);
+  ~Server() { Stop(); }
+
+  llvm::Error Start(const Socket::SocketProtocol &protocol,
+                    const std::string &name);
+
+  void Stop();
+
+  void AddTool(std::unique_ptr<Tool> tool);
+  void AddHandler(
+      llvm::StringRef method,
+      std::function<protocol::Response(const protocol::Request &)> handler);
+
+private:
+  llvm::Error Run(std::unique_ptr<JSONTransport> transport);
+  llvm::Expected<protocol::Response> Handle(protocol::Request request);
+
+  protocol::Response InitializeHandler(const protocol::Request &);
+  protocol::Response ToolsListHandler(const protocol::Request &);
+  protocol::Response ToolsCallHandler(const protocol::Request &);
+
+  protocol::Capabilities GetCapabilities();
+
+  std::string m_name;
+  std::string m_version;
+
+  bool m_running = false;
+
+  MainLoop m_loop;
+  std::thread m_loop_thread;
+
+  std::unique_ptr<Socket> m_listener;
+  std::vector<MainLoopBase::ReadHandleUP> m_read_handles;
+  std::vector<std::pair<lldb::IOObjectSP, std::thread>> m_clients;
+
+  std::mutex m_server_mutex;
+  llvm::StringMap<std::unique_ptr<Tool>> m_tools;
+  llvm::StringMap<std::function<protocol::Response(const protocol::Request &)>>
+      m_handlers;
+};
+} // namespace lldb_private::mcp
+
+#endif
diff --git a/lldb/include/lldb/MCP/Tool.h b/lldb/include/lldb/MCP/Tool.h
new file mode 100644
index 0000000000000..0fb2db98716ad
--- /dev/null
+++ b/lldb/include/lldb/MCP/Tool.h
@@ -0,0 +1,45 @@
+//===- Tool.h 
-------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_TOOLS_LLDB_MCP_TOOL_H
+#define LLDB_TOOLS_LLDB_MCP_TOOL_H
+
+#include "Protocol.h"
+#include "llvm/Support/JSON.h"
+#include <string>
+
+namespace lldb_private::mcp {
+
+class Tool {
+public:
+  Tool(std::string name, std::string description);
+  virtual ~Tool() = default;
+
+  virtual protocol::TextResult Call(const llvm::json::Value &args) = 0;
+
+  virtual std::optional<llvm::json::Value> GetSchema() const {
+    return std::nullopt;
+  }
+
+  protocol::ToolDefinition GetDefinition() const;
+
+  const std::string &GetName() { return m_name; }
+
+protected:
+  void SetAnnotations(protocol::ToolAnnotations annotations) {
+    m_annotations.emplace(std::move(annotations));
+  }
+
+private:
+  std::string m_name;
+  std::string m_description;
+  std::optional<protocol::ToolAnnotations> m_annotations;
+};
+} // namespace lldb_private::mcp
+
+#endif
diff --git a/lldb/source/CMakeLists.txt b/lldb/source/CMakeLists.txt
index 51c9f9c90826e..d35521ffd5c22 100644
--- a/lldb/source/CMakeLists.txt
+++ b/lldb/source/CMakeLists.txt
@@ -9,6 +9,7 @@ add_subdirectory(Expression)
 add_subdirectory(Host)
 add_subdirectory(Initialization)
 add_subdirectory(Interpreter)
+add_subdirectory(MCP)
 add_subdirectory(Plugins)
 add_subdirectory(Symbol)
 add_subdirectory(Target)
diff --git a/lldb/source/Commands/CMakeLists.txt 
b/lldb/source/Commands/CMakeLists.txt
index 1ea51acec5f15..2d29653971de8 100644
--- a/lldb/source/Commands/CMakeLists.txt
+++ b/lldb/source/Commands/CMakeLists.txt
@@ -17,6 +17,7 @@ add_lldb_library(lldbCommands NO_PLUGIN_DEPENDENCIES
   CommandObjectHelp.cpp
   CommandObjectLanguage.cpp
   CommandObjectLog.cpp
+  CommandObjectMCP.cpp
   CommandObjectMemory.cpp
   CommandObjectMemoryTag.cpp
   CommandObjectMultiword.cpp
@@ -51,6 +52,7 @@ add_lldb_library(lldbCommands NO_PLUGIN_DEPENDENCIES
     lldbDataFormatters
     lldbExpression
     lldbHost
+    lldbMCP
     lldbInterpreter
     lldbSymbol
     lldbTarget
diff --git a/lldb/source/Commands/CommandObjectMCP.cpp 
b/lldb/source/Commands/CommandObjectMCP.cpp
new file mode 100644
index 0000000000000..781995fcc9318
--- /dev/null
+++ b/lldb/source/Commands/CommandObjectMCP.cpp
@@ -0,0 +1,162 @@
+//===-- CommandObjectMCP.cpp 
----------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "CommandObjectMCP.h"
+#include "lldb/Host/Socket.h"
+#include "lldb/Interpreter/CommandInterpreter.h"
+#include "lldb/Interpreter/CommandReturnObject.h"
+#include "lldb/MCP/Server.h"
+#include "lldb/Utility/UriParser.h"
+#include "llvm/Support/FormatAdapters.h"
+
+using namespace llvm;
+using namespace lldb;
+using namespace lldb_private;
+
+#define LLDB_OPTIONS_mcp
+#include "CommandOptions.inc"
+
+static std::optional<mcp::Server> g_mcp_server;
+
+class LLDBCommandTool : public mcp::Tool {
+public:
+  LLDBCommandTool(std::string name, std::string description, Debugger 
&debugger)
+      : mcp::Tool(std::move(name), std::move(description)),
+        m_debugger(debugger) {}
+  ~LLDBCommandTool() = default;
+
+  virtual mcp::protocol::TextResult
+  Call(const llvm::json::Value &args) override {
+    std::string arguments;
+    if (const json::Object *args_obj = args.getAsObject()) {
+      if (const json::Value *s = args_obj->get("arguments")) {
+        arguments = s->getAsString().value_or("");
+      }
+    }
+
+    CommandReturnObject result(/*colors=*/false);
+    m_debugger.GetCommandInterpreter().HandleCommand(arguments.c_str(),
+                                                     eLazyBoolYes, result);
+
+    std::string output;
+    llvm::StringRef output_str = result.GetOutputString();
+    if (!output_str.empty())
+      output += output_str.str();
+
+    std::string err_str = result.GetErrorString();
+    if (!err_str.empty()) {
+      if (!output.empty())
+        output += '\n';
+      output += err_str;
+    }
+
+    mcp::protocol::TextResult text_result;
+    text_result.content.emplace_back(mcp::protocol::TextContent{{output}});
+    return text_result;
+  }
+
+  virtual std::optional<llvm::json::Value> GetSchema() const override {
+    llvm::json::Object str_type{{"type", "string"}};
+    llvm::json::Object properties{{"arguments", std::move(str_type)}};
+    llvm::json::Object schema{{"type", "object"},
+                              {"properties", std::move(properties)}};
+    return schema;
+  }
+
+private:
+  Debugger &m_debugger;
+};
+
+static llvm::Expected<std::pair<Socket::SocketProtocol, std::string>>
+validateConnection(llvm::StringRef conn) {
+  auto uri = lldb_private::URI::Parse(conn);
+
+  if (uri && (uri->scheme == "tcp" || uri->scheme == "connect" ||
+              !uri->hostname.empty() || uri->port)) {
+    return std::make_pair(
+        Socket::ProtocolTcp,
+        formatv("[{0}]:{1}", uri->hostname.empty() ? "0.0.0.0" : uri->hostname,
+                uri->port.value_or(0)));
+  }
+
+  if (uri && (uri->scheme == "unix" || uri->scheme == "unix-connect" ||
+              uri->path != "/")) {
+    return std::make_pair(Socket::ProtocolUnixDomain, uri->path.str());
+  }
+
+  return llvm::createStringError(
+      "Unsupported connection specifier, expected 'unix-connect:///path' or "
+      "'connect://[host]:port', got '%s'.",
+      conn.str().c_str());
+}
+
+class CommandObjectMCPStart : public CommandObjectParsed {
+public:
+  CommandObjectMCPStart(CommandInterpreter &interpreter)
+      : CommandObjectParsed(interpreter, "mcp start", "start MCP server",
+                            "mcp start <connection>") {
+    AddSimpleArgumentList(lldb::eArgTypeConnectURL, eArgRepeatOptional);
+  }
+
+  ~CommandObjectMCPStart() override = default;
+
+protected:
+  void DoExecute(Args &args, CommandReturnObject &result) override {
+    if (args.GetArgumentCount() != 1) {
+      result.AppendError("no connection specified");
+      return;
+    }
+
+    llvm::StringRef connection = args.GetArgumentAtIndex(0);
+    auto maybeProtoclAndName = validateConnection(connection);
+    if (auto error = maybeProtoclAndName.takeError()) {
+      result.AppendErrorWithFormatv("{0}", 
llvm::fmt_consume(std::move(error)));
+      return;
+    }
+
+    if (!g_mcp_server) {
+      g_mcp_server.emplace("lldb-mcp", "0.1.0");
+      g_mcp_server->AddTool(std::make_unique<LLDBCommandTool>(
+          "lldb_command", "Run an lldb command.", GetDebugger()));
+    }
+
+    Socket::SocketProtocol protocol;
+    std::string name;
+    std::tie(protocol, name) = *maybeProtoclAndName;
+    if (llvm::Error error = g_mcp_server->Start(protocol, name)) {
+      result.AppendErrorWithFormatv("{0}", 
llvm::fmt_consume(std::move(error)));
+      return;
+    }
+  }
+};
+
+class CommandObjectMCPStop : public CommandObjectParsed {
+public:
+  CommandObjectMCPStop(CommandInterpreter &interpreter)
+      : CommandObjectParsed(interpreter, "mcp stop", "stop MCP server",
+                            "mcp stop") {}
+
+  ~CommandObjectMCPStop() override = default;
+
+protected:
+  void DoExecute(Args &args, CommandReturnObject &result) override {
+    if (g_mcp_server)
+      g_mcp_server->Stop();
+  }
+};
+
+CommandObjectMCP::CommandObjectMCP(CommandInterpreter &interpreter)
+    : CommandObjectMultiword(interpreter, "mcp", "Start an MCP server.",
+                             "mcp") {
+  LoadSubCommand("start",
+                 CommandObjectSP(new CommandObjectMCPStart(interpreter)));
+  LoadSubCommand("stop",
+                 CommandObjectSP(new CommandObjectMCPStop(interpreter)));
+}
+
+CommandObjectMCP::~CommandObjectMCP() = default;
diff --git a/lldb/source/Commands/CommandObjectMCP.h 
b/lldb/source/Commands/CommandObjectMCP.h
new file mode 100644
index 0000000000000..7f5a08452fdfc
--- /dev/null
+++ b/lldb/source/Commands/CommandObjectMCP.h
@@ -0,0 +1,24 @@
+//===-- CommandObjectMCP.h 
------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLDB_SOURCE_COMMANDS_COMMANDOBJECTMCP_H
+#define LLDB_SOURCE_COMMANDS_COMMANDOBJECTMCP_H
+
+#include "lldb/Interpreter/CommandObjectMultiword.h"
+
+namespace lldb_private {
+
+class CommandObjectMCP : public CommandObjectMultiword {
+public:
+  CommandObjectMCP(CommandInterpreter &interpreter);
+  ~CommandObjectMCP() override;
+};
+
+} // namespace lldb_private
+
+#endif // LLDB_SOURCE_COMMANDS_COMMANDOBJECTMCP_H
diff --git a/lldb/source/Interpreter/CommandInterpreter.cpp 
b/lldb/source/Interpreter/CommandInterpreter.cpp
index 4f9ae104dedea..705fe38c39d63 100644
--- a/lldb/source/Interpreter/CommandInterpreter.cpp
+++ b/lldb/source/Interpreter/CommandInterpreter.cpp
@@ -26,6 +26,7 @@
 #include "Commands/CommandObjectHelp.h"
 #include "Commands/CommandObjectLanguage.h"
 #include "Commands/CommandObjectLog.h"
+#include "Commands/CommandObjectMCP.h"
 #include "Commands/CommandObjectMemory.h"
 #include "Commands/CommandObjectPlatform.h"
 #include "Commands/CommandObjectPlugin.h"
@@ -570,6 +571,7 @@ void CommandInterpreter::LoadCommandDictionary() {
   REGISTER_COMMAND_OBJECT("gui", CommandObjectGUI);
   REGISTER_COMMAND_OBJECT("help", CommandObjectHelp);
   REGISTER_COMMAND_OBJECT("log", CommandObjectLog);
+  REGISTER_COMMAND_OBJECT("mcp", CommandObjectMCP);
   REGISTER_COMMAND_OBJECT("memory", CommandObjectMemory);
   REGISTER_COMMAND_OBJECT("platform", CommandObjectPlatform);
   REGISTER_COMMAND_OBJECT("plugin", CommandObjectPlugin);
diff --git a/lldb/source/MCP/CMakeLists.txt b/lldb/source/MCP/CMakeLists.txt
new file mode 100644
index 0000000000000..a2ac0bdba2912
--- /dev/null
+++ b/lldb/source/MCP/CMakeLists.txt
@@ -0,0 +1,13 @@
+add_lldb_library(lldbMCP
+  MCPError.cpp
+  Protocol.cpp
+  Server.cpp
+  Tool.cpp
+
+  LINK_COMPONENTS
+    Support
+
+  LINK_LIBS
+    lldbHost
+    lldbUtility
+)
diff --git a/lldb/source/MCP/MCPError.cpp b/lldb/source/MCP/MCPError.cpp
new file mode 100644
index 0000000000000..b4768b75a4617
--- /dev/null
+++ b/lldb/source/MCP/MCPError.cpp
@@ -0,0 +1,31 @@
+//===-- MCPError.cpp 
------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/MCP/MCPError.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/raw_ostream.h"
+#include <system_error>
+
+namespace lldb_private::mcp {
+
+char MCPError::ID;
+
+MCPError::MCPError(std::string message, int64_t error_code)
+    : m_message(message), m_error_code(error_code) {}
+
+void MCPError::log(llvm::raw_ostream &OS) const { OS << m_message; }
+
+std::error_code MCPError::convertToErrorCode() const {
+  return llvm::inconvertibleErrorCode();
+}
+
+protocol::Error MCPError::toProtcolError() const {
+  return protocol::Error{m_error_code, m_message, std::nullopt};
+}
+
+} // namespace lldb_private::mcp
diff --git a/lldb/source/MCP/Protocol.cpp b/lldb/source/MCP/Protocol.cpp
new file mode 100644
index 0000000000000..1a74746400a30
--- /dev/null
+++ b/lldb/source/MCP/Protocol.cpp
@@ -0,0 +1,180 @@
+//===- Protocol.cpp 
-------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/MCP/Protocol.h"
+#include "llvm/Support/JSON.h"
+
+using namespace llvm;
+
+namespace lldb_private::mcp::protocol {
+
+static bool mapRaw(const json::Value &Params, StringLiteral Prop,
+                   std::optional<json::Value> &V, json::Path P) {
+  const auto *O = Params.getAsObject();
+  if (!O) {
+    P.report("expected object");
+    return false;
+  }
+  const json::Value *E = O->get(Prop);
+  if (E)
+    V = std::move(*E);
+  return true;
+}
+
+llvm::json::Value toJSON(const Request &R) {
+  json::Object Result{{"jsonrpc", "2.0"}, {"id", R.id}, {"method", R.method}};
+  if (R.params)
+    Result.insert({"params", R.params});
+  return Result;
+}
+
+bool fromJSON(const llvm::json::Value &V, Request &R, llvm::json::Path P) {
+  llvm::json::ObjectMapper O(V, P);
+  if (!O || !O.map("id", R.id) || !O.map("method", R.method))
+    return false;
+  return mapRaw(V, "params", R.params, P);
+}
+
+llvm::json::Value toJSON(const Error &E) {
+  return llvm::json::Object{
+      {"code", E.code}, {"message", E.message}, {"data", E.data}};
+}
+
+bool fromJSON(const llvm::json::Value &V, Error &E, llvm::json::Path P) {
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.map("code", E.code) && O.map("message", E.message) &&
+         O.map("data", E.data);
+}
+
+llvm::json::Value toJSON(const ProtocolError &PE) {
+  return llvm::json::Object{{"id", PE.id}, {"error", toJSON(PE.error)}};
+}
+
+bool fromJSON(const llvm::json::Value &V, ProtocolError &PE,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.map("id", PE.id) && O.map("error", PE.error);
+}
+
+llvm::json::Value toJSON(const Response &R) {
+  llvm::json::Object Result{{"jsonrpc", "2.0"}, {"id", R.id}};
+  if (R.result)
+    Result.insert({"result", R.result});
+  if (R.error)
+    Result.insert({"error", R.error});
+  return Result;
+}
+
+bool fromJSON(const llvm::json::Value &V, Response &R, llvm::json::Path P) {
+  return true;
+}
+
+llvm::json::Value toJSON(const Notification &N) {
+  llvm::json::Object Result{{"jsonrpc", "2.0"}, {"method", N.method}};
+  if (N.params)
+    Result.insert({"params", N.params});
+  return Result;
+}
+
+bool fromJSON(const llvm::json::Value &V, Notification &N, llvm::json::Path P) 
{
+  llvm::json::ObjectMapper O(V, P);
+  if (!O || !O.map("method", N.method))
+    return false;
+  auto *Obj = V.getAsObject();
+  if (!Obj)
+    return false;
+  if (auto *Params = Obj->get("params"))
+    N.params = *Params;
+  return true;
+}
+
+llvm::json::Value toJSON(const ToolCapability &TC) {
+  return llvm::json::Object{{"listChanged", TC.listChanged}};
+}
+
+bool fromJSON(const llvm::json::Value &V, ToolCapability &TC,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.map("listChanged", TC.listChanged);
+}
+
+llvm::json::Value toJSON(const Capabilities &C) {
+  return llvm::json::Object{{"tools", C.tools}};
+}
+
+bool fromJSON(const llvm::json::Value &V, Capabilities &C, llvm::json::Path P) 
{
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.map("tool", C.tools);
+}
+
+llvm::json::Value toJSON(const TextContent &TC) {
+  return llvm::json::Object{{"type", "text"}, {"text", TC.text}};
+}
+
+bool fromJSON(const llvm::json::Value &V, TextContent &TC, llvm::json::Path P) 
{
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.map("text", TC.text);
+}
+
+llvm::json::Value toJSON(const TextResult &TR) {
+  return llvm::json::Object{{"content", TR.content}, {"isError", TR.isError}};
+}
+
+bool fromJSON(const llvm::json::Value &V, TextResult &TR, llvm::json::Path P) {
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.map("content", TR.content) && O.map("isError", TR.isError);
+}
+
+llvm::json::Value toJSON(const ToolAnnotations &TA) {
+  llvm::json::Object Result;
+  if (TA.title)
+    Result.insert({"title", TA.title});
+  if (TA.readOnlyHint)
+    Result.insert({"readOnlyHint", TA.readOnlyHint});
+  if (TA.destructiveHint)
+    Result.insert({"destructiveHint", TA.destructiveHint});
+  if (TA.idempotentHint)
+    Result.insert({"idempotentHint", TA.idempotentHint});
+  if (TA.openWorldHint)
+    Result.insert({"openWorldHint", TA.openWorldHint});
+  return Result;
+}
+
+bool fromJSON(const llvm::json::Value &V, ToolAnnotations &TA,
+              llvm::json::Path P) {
+  llvm::json::ObjectMapper O(V, P);
+  return O && O.mapOptional("title", TA.title) &&
+         O.mapOptional("readOnlyHint", TA.readOnlyHint) &&
+         O.mapOptional("destructiveHint", TA.destructiveHint) &&
+         O.mapOptional("idempotentHint", TA.idempotentHint) &&
+         O.mapOptional("openWorldHint", TA.openWorldHint);
+}
+
+llvm::json::Value toJSON(const ToolDefinition &TD) {
+  llvm::json::Object Result{{"name", TD.name}};
+  if (TD.description)
+    Result.insert({"description", TD.description});
+  if (TD.inputSchema)
+    Result.insert({"inputSchema", TD.inputSchema});
+  if (TD.annotations)
+    Result.insert({"annotations", TD.annotations});
+  return Result;
+}
+
+bool fromJSON(const llvm::json::Value &V, ToolDefinition &TD,
+              llvm::json::Path P) {
+
+  llvm::json::ObjectMapper O(V, P);
+  if (!O || !O.map("name", TD.name) ||
+      !O.mapOptional("description", TD.description) ||
+      !O.mapOptional("annotations", TD.annotations))
+    return false;
+  return mapRaw(V, "inputSchema", TD.inputSchema, P);
+}
+
+} // namespace lldb_private::mcp::protocol
diff --git a/lldb/source/MCP/Server.cpp b/lldb/source/MCP/Server.cpp
new file mode 100644
index 0000000000000..91885572a9474
--- /dev/null
+++ b/lldb/source/MCP/Server.cpp
@@ -0,0 +1,251 @@
+//===- Server.cpp 
---------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/MCP/Server.h"
+#include "lldb/MCP/MCPError.h"
+#include "lldb/Utility/LLDBLog.h"
+#include "lldb/Utility/Log.h"
+#include "llvm/ADT/StringExtras.h"
+#include "llvm/Support/Threading.h"
+#include <thread>
+
+using namespace lldb_private::mcp;
+using namespace llvm;
+
+Server::Server(std::string name, std::string version)
+    : m_name(std::move(name)), m_version(std::move(version)) {
+
+  AddHandler("initialize", std::bind(&Server::InitializeHandler, this,
+                                     std::placeholders::_1));
+  AddHandler("tools/list",
+             std::bind(&Server::ToolsListHandler, this, 
std::placeholders::_1));
+  AddHandler("tools/call",
+             std::bind(&Server::ToolsCallHandler, this, 
std::placeholders::_1));
+}
+
+llvm::Expected<protocol::Response> Server::Handle(protocol::Request request) {
+  auto it = m_handlers.find(request.method);
+  if (it != m_handlers.end())
+    return it->second(request);
+
+  return make_error<MCPError>(
+      llvm::formatv("no handler for request: {0}", request.method).str(), 1);
+}
+
+llvm::Error Server::Start(const Socket::SocketProtocol &protocol,
+                          const std::string &name) {
+  std::lock_guard<std::mutex> guard(m_server_mutex);
+
+  if (m_running)
+    return llvm::createStringError("server already running");
+
+  Status status;
+  m_listener = Socket::Create(protocol, status);
+  if (status.Fail())
+    return status.takeError();
+
+  status = m_listener->Listen(name, /*backlog=*/5);
+  if (status.Fail())
+    return status.takeError();
+
+  std::string address =
+      llvm::join(m_listener->GetListeningConnectionURI(), ", ");
+  Log *log = GetLog(LLDBLog::Host);
+  LLDB_LOG(log, "MCP server started with connection listeners: {0}", address);
+
+  auto handles = m_listener->Accept(m_loop, [=](std::unique_ptr<Socket> sock) {
+    std::lock_guard<std::mutex> guard(m_server_mutex);
+
+    const std::string client_name =
+        llvm::formatv("client-{0}", m_clients.size() + 1).str();
+    LLDB_LOG(log, "client {0} connected", client_name);
+
+    lldb::IOObjectSP io(std::move(sock));
+
+    m_clients.emplace_back(io, [=]() {
+      llvm::set_thread_name(client_name + "-runloop");
+      if (auto Err = Run(std::make_unique<JSONRPCTransport>(io, io)))
+        LLDB_LOG_ERROR(GetLog(LLDBLog::Host), std::move(Err), "MCP Error: 
{0}");
+    });
+  });
+  if (llvm::Error error = handles.takeError())
+    return error;
+
+  m_read_handles = std::move(*handles);
+  m_loop_thread = std::thread([=] {
+    llvm::set_thread_name("mcp-runloop");
+    m_loop.Run();
+  });
+
+  return llvm::Error::success();
+}
+
+void Server::Stop() {
+  {
+    std::lock_guard<std::mutex> guard(m_server_mutex);
+    m_running = false;
+  }
+
+  // Stop accepting new connections.
+  m_loop.AddPendingCallback(
+      [](MainLoopBase &loop) { loop.RequestTermination(); });
+
+  // Wait for the main loop to exit.
+  if (m_loop_thread.joinable())
+    m_loop_thread.join();
+
+  // Wait for all our clients to exit.
+  for (auto &client : m_clients) {
+    client.first->Close();
+    if (client.second.joinable())
+      client.second.join();
+  }
+
+  {
+    std::lock_guard<std::mutex> guard(m_server_mutex);
+    m_listener.reset();
+    m_read_handles.clear();
+    m_clients.clear();
+  }
+}
+
+llvm::Error Server::Run(std::unique_ptr<JSONTransport> transport) {
+  Log *log = GetLog(LLDBLog::Host);
+
+  while (true) {
+    llvm::Expected<protocol::Request> request =
+        transport->Read<protocol::Request>(std::chrono::seconds(1));
+    if (request.errorIsA<TransportEOFError>() ||
+        request.errorIsA<TransportInvalidError>()) {
+      consumeError(request.takeError());
+      break;
+    }
+
+    if (request.errorIsA<TransportTimeoutError>()) {
+      consumeError(request.takeError());
+      continue;
+    }
+
+    if (llvm::Error err = request.takeError()) {
+      LLDB_LOG_ERROR(log, std::move(err), "{0}");
+      continue;
+    }
+
+    protocol::Response response;
+    llvm::Expected<protocol::Response> maybe_response = Handle(*request);
+    if (!maybe_response) {
+      llvm::handleAllErrors(
+          maybe_response.takeError(),
+          [&](const MCPError &err) {
+            response.error.emplace(err.toProtcolError());
+          },
+          [&](const llvm::ErrorInfoBase &err) {
+            response.error.emplace();
+            response.error->code = -1;
+            response.error->message = err.message();
+          });
+    } else {
+      response = *maybe_response;
+    }
+
+    response.id = request->id;
+
+    if (llvm::Error err = transport->Write(response))
+      return err;
+  }
+
+  return llvm::Error::success();
+}
+
+protocol::Capabilities Server::GetCapabilities() {
+  protocol::Capabilities capabilities;
+  capabilities.tools.listChanged = true;
+  return capabilities;
+}
+
+void Server::AddTool(std::unique_ptr<Tool> tool) {
+  std::lock_guard<std::mutex> guard(m_server_mutex);
+
+  if (!tool)
+    return;
+  m_tools[tool->GetName()] = std::move(tool);
+}
+
+void Server::AddHandler(
+    llvm::StringRef method,
+    std::function<protocol::Response(const protocol::Request &)> handler) {
+  std::lock_guard<std::mutex> guard(m_server_mutex);
+
+  m_handlers[method] = std::move(handler);
+}
+
+protocol::Response Server::InitializeHandler(const protocol::Request &request) 
{
+  protocol::Response response;
+
+  std::string protocol_version = protocol::kProtocolVersion.str();
+  if (request.params) {
+    if (const json::Object *param_obj = request.params->getAsObject()) {
+      if (const json::Value *val = param_obj->get("protocolVersion")) {
+        if (auto protocol_version_str = val->getAsString()) {
+          protocol_version = *protocol_version_str;
+        }
+      }
+    }
+  }
+
+  response.result.emplace(llvm::json::Object{
+      {"protocolVersion", protocol_version},
+      {"capabilities", GetCapabilities()},
+      {"serverInfo",
+       llvm::json::Object{{"name", m_name}, {"version", m_version}}}});
+  return response;
+}
+
+protocol::Response Server::ToolsListHandler(const protocol::Request &request) {
+  protocol::Response response;
+
+  llvm::json::Array tools;
+  for (const auto &tool : m_tools)
+    tools.emplace_back(toJSON(tool.second->GetDefinition()));
+
+  response.result.emplace(llvm::json::Object{{"tools", std::move(tools)}});
+
+  return response;
+}
+
+protocol::Response Server::ToolsCallHandler(const protocol::Request &request) {
+  protocol::Response response;
+
+  if (!request.params)
+    return response;
+
+  const json::Object *param_obj = request.params->getAsObject();
+  if (!param_obj)
+    return response;
+
+  const json::Value *name = param_obj->get("name");
+  if (!name)
+    return response;
+
+  llvm::StringRef tool_name = name->getAsString().value_or("");
+  if (tool_name.empty())
+    return response;
+
+  auto it = m_tools.find(tool_name);
+  if (it == m_tools.end())
+    return response;
+
+  const json::Value *args = param_obj->get("arguments");
+  if (!args)
+    return response;
+
+  protocol::TextResult text_result = it->second->Call(*args);
+  response.result.emplace(toJSON(text_result));
+
+  return response;
+}
diff --git a/lldb/source/MCP/Tool.cpp b/lldb/source/MCP/Tool.cpp
new file mode 100644
index 0000000000000..9d2e82723c2f5
--- /dev/null
+++ b/lldb/source/MCP/Tool.cpp
@@ -0,0 +1,28 @@
+//===- Tool.cpp 
-----------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM 
Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#include "lldb/MCP/Tool.h"
+
+using namespace lldb_private::mcp;
+
+Tool::Tool(std::string name, std::string description)
+    : m_name(std::move(name)), m_description(std::move(description)) {}
+
+protocol::ToolDefinition Tool::GetDefinition() const {
+  protocol::ToolDefinition definition;
+  definition.name = m_name;
+  definition.description.emplace(m_description);
+
+  if (std::optional<llvm::json::Value> input_schema = GetSchema())
+    definition.inputSchema = *input_schema;
+
+  if (m_annotations)
+    definition.annotations = m_annotations;
+
+  return definition;
+}

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