4.2 KiB
Model Context Protocol (MCP)
LLDB supports the Model Context Protocol (MCP). This structured, machine-friendly protocol allows AI models to access and interact with external tools, for example debuggers. Using MCP, an AI agent can execute LLDB commands to control the debugger: set breakpoints, inspect memory, step through code. This can range from helping you run a specific command you cannot immediately remember, to a fully agent-driven debugging experience.
MCP Server
To start the MCP server in LLDB, use the protocol-server start command.
Specify MCP as the protocol and provide a URI to listen on. For example, to
start listening for local TCP connections on port 59999, use the following
command:
(lldb) protocol-server start MCP listen://localhost:59999
MCP server started with connection listeners: connection://[::1]:59999, connection://[127.0.0.1]:59999
The server will automatically stop when exiting LLDB, or it can be stopped
explicitly with the protocol-server stop command.
(lldb) protocol-server stop MCP
The commands will fail if a server is already running or not running respectively.
MCP Client
MCP uses standard input/output (stdio) for communication between client and
server. The exact configuration depends on the client, but most applications
allow you to specify an MCP server as a binary and arguments. This means that
you need to use something like netcat to connect to LLDB's MCP server and
forward communication over stdio over the network connection.
┌──────────┐ ┌──────────┐ ┌──────────┐
│ │ │ │ │ │
│ LLDB ├─────socket────┤ netcat ├─────stdio─────┤MCP Client│
│ │ │ │ │ │
└──────────┘ └──────────┘ └──────────┘
Configuration example for Claude Code:
{
"mcpServers": {
"tool": {
"command": "/usr/bin/nc",
"args": ["localhost", "59999"]
}
}
}
Configuration example for Visual Studio Code:
{
"mcp": {
"servers": {
"lldb": {
"type": "stdio",
"command": "/usr/bin/nc",
"args": ["localhost", "59999"]
}
}
}
}
Tools
Tools are a primitive in the Model Context Protocol that enable servers to expose functionality to clients.
LLDB's MCP integration exposes one tool, named lldb_command which allows the
model to run the same commands a user would type in the LLDB command
interpreter. It takes two arguments:
- The unique debugger ID as a number.
- The command and its arguments as a string.
Resources
Resources are a primitive in the Model Context Protocol that allow servers to expose content that can be read by clients.
LLDB's MCP integration exposes a resource for each debugger and target instance. Debugger resources are accessible using the following URI:
lldb://debugger/<debugger id>
Example output:
{
"contents": [
{
"uri": "lldb://debugger/1",
"mimeType": "application/json",
"text": "{\"debugger_id\":1,\"name\":\"debugger_1\",\"num_targets\":1}"
}
]
}
Debuggers can contain one or more targets, which are accessible using the following URI:
lldb://debugger/<debugger id>/target/<target idx>
Example output:
{
"contents": [
{
"uri": "lldb://debugger/1/target/0",
"mimeType": "application/json",
"text": "{\"arch\":\"arm64-apple-macosx26.0.0\",\"debugger_id\":1,\"dummy\":false,\"path\":\"/bin/count\",\"platform\":\"host\",\"selected\":true,\"target_idx\":0}"
}
]
}
Note that unlike the debugger id, which is unique, the target index is not stable and may be reused when a target is removed and a new target is added.
Troubleshooting
The MCP server uses the Host log channel. You can enable logging with the
log enable command.
(lldb) log enable lldb host