Command line (CLI)

The binary is invoked as modelcontextprotocol. Exactly one server must be selected, in one of two equivalent styles:

• Subcommand form — modelcontextprotocol <server> [options] [DIR ...]
• Flag form — modelcontextprotocol --<server> [options] [DIR ...]

The flag form exists so the binary can be wired into MCP client configurations that cannot pass subcommands. Both forms are normalized into the same command internally.

Commands

Command	Required arguments	Options	Server
filesystem <DIR> [DIR ...]	at least one directory	—	mcp-filesystem
fetch	—	--ignore-robots-txt, --user-agent <UA>, --proxy-url <URL>	mcp-fetch
memory	—	--memory-file <PATH>	mcp-memory
shell <DIR> [DIR ...]	at least one directory	—	mcp-shell

Equivalent flag forms:

Flag form	Equivalent to
--filesystem <DIR> [DIR ...]	filesystem <DIR> [DIR ...]
--fetch	fetch
--memory	memory
--shell <DIR> [DIR ...]	shell <DIR> [DIR ...]

Fetch options

Option	Description
--ignore-robots-txt	Skip robots.txt checks for the fetch tool (the fetch prompt never checks robots.txt regardless)
--user-agent <USER_AGENT>	Custom User-Agent header used for all requests, replacing both default agents
--proxy-url <URL>	Route all requests through this HTTP(S) proxy

Memory options

Option	Description
--memory-file <PATH>	Location of the memory JSONL file; overrides the MEMORY_FILE_PATH environment variable

Selection and conflict rules

Cli::into_command enforces strict selection rules; any violation prints the usage summary to stderr and exits with code 1 instead of silently ignoring options:

• Exactly one server selector (subcommand or top-level flag) must be present.
• Server-specific options may only be combined with the server they belong to. Examples of rejected invocations:
  • --ignore-robots-txt or --proxy-url with filesystem, memory, or shell
  • --memory-file with fetch, filesystem, or shell
  • Two selectors at once (for example fetch --memory)
  • filesystem with no directory (directories are required for filesystem and shell)

Server startup also validates its arguments:

• filesystem / shell: each directory is expanded (~ → home), made absolute, and canonicalized. Directories that do not exist or are not directories are skipped with a warning; if no usable directory remains, the server exits with an error. See Security model.
• memory: the resolved memory file path is made absolute relative to the current working directory when needed.

Environment variables

Variable	Used by	Description
RUST_LOG	all servers	tracing filter. Defaults to modelcontextprotocol=warn when unset. Logs go to stderr with ANSI colors disabled; stdout carries only JSON-RPC messages
MEMORY_FILE_PATH	memory	Memory file location, overridden by --memory-file. Defaults to memory.jsonl in the current working directory
OPENROUTER_API_KEY	E2E suite only	API key for the ignored real-network acceptance suite (tests/openrouter_e2e.rs). Not read by any server
OPENROUTER_MODEL	E2E suite only	Model override accepted by the acceptance suite for diagnostics; the acceptance default is the exact alias ~deepseek/deepseek-v4-flash-latest. Not read by any server

Generic flags

• --help / -h — clap-generated help.
• --version / -V — prints the crate version (for example modelcontextprotocol 0.1.0).

Exit behavior

• Selection/validation errors: usage or error message on stderr, exit code 1.
• Once running, a server serves MCP over stdio until the transport closes (the client disconnects or the parent process exits), then exits cleanly.