Getting SDK Internal Logs

Internal logs of the MCP C++ SDK are disabled by default and can be enabled on demand for troubleshooting.

Option 1: Environment Variable (Fastest)

Set MCP_LOG_LEVEL (0-5, 0=Off, 4=Debug) before launching the process; logs are written straight to stderr:

MCP_LOG_LEVEL=4 ./your_mcp_server

Levels: Off=0 Error=1 Warning=2 Info=3 Debug=4 Trace=5. Use 4 for general debugging.

Option 2: Programmatic Hook (Integrate with Your Own Logging System)

Capture structured LogRecords through the global hook and forward them to your own logging backend:

#include <mcp/Log.hpp>

mcp::SetLogLevel(mcp::LogLevel::Debug);
mcp::SetLogHandler([](const mcp::LogRecord& r) {
    my_logger.log(static_cast<int>(r.level),
                  std::string(r.tag),
                  std::string(r.message));
});
// To restore the default stderr output:
// mcp::SetLogHandler(nullptr);

Notes:

• The hook is invoked synchronously on the thread emitting the log (including IO threads); the callback must be thread-safe.
• Do not call Close() inside the hook, otherwise it may self-join and deadlock.
• Exceptions thrown inside the hook are swallowed by the SDK and never propagate.

Configurable Bind Address

HttpServer now supports HttpServerOptions::bind_host (and StreamableHttpServerOptions::host) to specify the listening address, accepting IPv4/IPv6 literals (e.g. 127.0.0.1 / ::1 / ::, optionally wrapped in []); an empty string means listening on all IPv4 interfaces only (the default behavior).