fast-mcp-ssh

fast-mcp-ssh

SSH, SFTP and persistent shells for AI agents. One Rust binary, no runtime.

An MCP server that gives a model real SSH access:

• One connection per host, held open across calls.
• A PTY shell that remembers cd and export.
• SFTP instead of cat > file, and host-to-host copies that skip your disk.
• A screenshot of the remote desktop.
• Regex guards before anything leaves your machine.
• An append-only audit log of every call.

Answers come back as TOON, roughly 40 percent fewer tokens than JSON on tabular data.

Install

cargo install fast-mcp-ssh

Or a prebuilt binary from the latest release, checked against SHA256SUMS.txt. Linux and macOS ship x86_64 and aarch64, Windows x86_64.

Copy hosts.example.toml to ~/.fast-mcp-ssh/hosts.toml and fill in your hosts. Keys go in ~/.fast-mcp-ssh/keys/<name>; auth is key, agent or password.

Wire it up

.mcp.json, or claude_desktop_config.json for Claude Desktop:

{
  "mcpServers": {
    "ssh": {
      "type": "stdio",
      "command": "fast-mcp-ssh"
    }
  }
}

Same block in Claude Code, Cursor, Windsurf, Zed, VS Code Copilot and anything else that speaks MCP over stdio.

In the MCP registry it is mcp-name: io.github.klNuno/fast-mcp-ssh.

Tools

host is optional on every tool once [defaults] default_host is set.

Group	Tools
Run	exec exec_batch sh interrupt	One-shot, parallel fan-out, persistent PTY, Ctrl-C
Files	ls stat dn up cp wr mkdir rm tail	SFTP, plus tail -n / tail -F in a bounded window
Visual	shot	Screenshots the remote desktop, downscaled before it reaches the model
Ops	facts sys svc	Cached host profile, parsed ps/df/mem/net, systemd units
Session	hosts ping disconnect disconnect_all reload shells	Discovery and lifecycle; reload swaps config without a restart, shells closes named PTYs
Network	forward unforward forwards	Local TCP forwards over the same connection

Every tool carries MCP annotations (readOnlyHint, destructiveHint, idempotentHint, openWorldHint) so a client can gate destructive calls.

Host-to-host copy

cp moves a file from one configured host to another. The bytes never land on your disk and never reach the model, and a sha256 is compared on both ends before success. Guards cover the destination too, so a read-only target still refuses the write.

Remote screenshots

shot hands the model an image instead of a wall of text. It uses whichever of grim, gnome-screenshot, spectacle, ImageMagick import or scrot the host has, covering X11 and wlroots Wayland, and downscales locally so a 4K screen is not a multi-megabyte payload.

Protocol

Speaks stateless MCP (2026-07-28) and every revision back to 2024-11-05, picked per peer. Stateless changes three things:

• Confirmations come back as an input_required result the client answers and retries (SEP-2322), because a server may no longer open a request of its own. Older peers keep elicitation/create.
• Long calls hand back a task handle to poll (SEP-2663): exec past its 60s timeout, tail with follow=true. Clients without the extension keep the blocking call.
• tools/list is sorted, so it is byte-identical between restarts, and carries a one hour ttlMs (SEP-2549). A client's prompt cache keeps hitting.

Shells are unaffected. A PTY has always been addressed by the host and session arguments of the call, which is the explicit handle stateless wants.

Security

Guards run before any SSH packet leaves. deny_patterns refuse outright, confirm_patterns ask the user, a client that cannot answer is denied, and read_only = true blocks anything that looks like a write.

Paths are checked on both sides: remote reads of keys, shadow files and cloud credentials, local writes into your ~/.bashrc or an autostart folder. Every path-taking tool runs both checks, tail included, and re-checks once the server has resolved the path, so a symlink cannot launder a blocked target. A path that will not resolve refuses the call.

Host keys are pinned, TOFU by default, strict and per-host fingerprints available. Every call lands in ~/.fast-mcp-ssh/audit.log as NDJSON, with credentials scrubbed.

Guards stop accidents, not an adversary who controls the model. Scope the remote account accordingly. Threat model: SECURITY.md. Version history: CHANGELOG.md.

Benchmark

50 iterations per scenario, same Linux host, same LAN, same SSH key, client on Windows 11. Medians, lower is better, measured on 0.5.0. Reproduce with benchmark/, raw runs in benchmark/results/.

	fast-mcp-ssh	mcp-ssh-manager	ssh-mcp-server
Cold start	48 ms	280 ms	260 ms
exec echo ok	2.2 ms	89.7 ms	46.7 ms
exec uname -a; whoami; pwd	3.6 ms	90.9 ms	50.6 ms
exec seq 1 5000 (~29 KB)	19.6 ms	90.4 ms 1	49.2 ms
Write a 1 KB file	1.1 ms	89.9 ms	47.9 ms
Read a 1 KB file	1.7 ms	90.3 ms	48.9 ms
Tool surface, sent every session	26 tools, 21.1 KB	37 tools, 39.9 KB	4 tools, 1.7 KB

Both alternatives are Node, so ~250 ms of their cold start is the runtime booting. The steady-state gap is the connection: fast-mcp-ssh holds one SSH session per host and opens a channel per call, the other two reconnect. Writes go over SFTP here, through a cat > file heredoc there.

Development

cargo install --path .        # build and install from a clone
cargo test                    # unit tests
cargo clippy --all-targets    # no warnings allowed in CI
./scripts/test-sh.ps1         # end-to-end against a real host (Windows)

Never write to stdout outside the MCP transport: a stray println! corrupts the JSON-RPC stream and the client disconnects without an error. tracing macros go to stderr and are safe.

License

MIT.

Footnotes

1. mcp-ssh-manager truncates that response to 12 KB, so it is not returning the same output. ssh-mcp-server returns raw stdout with no exit code, which is why its replies are the shortest and why a failed command looks like a successful one. ↩