Agent SSH

MCP server for persistent SSH sessions with tmux integration, port forwarding, and SFTP file writes — built for AI agent workflows.

Based on ssh-mcp-sessions by Justin Fry (MIT), with significant enhancements for agent reliability.

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What's improved over the original

The original fryjustinc/ssh-mcp-sessions provides 8 basic tools that execute commands directly in a hidden ssh2 shell buffer. This repo is a significant rework:

Architecture changes

Original	This repo
Commands run in a hidden ssh2 shell; output captured via in-memory buffer	Commands run inside a tmux session (ai); user can attach and watch live with tmux attach -t ai
Single end marker: printf '__MCP_DONE__%s%d\n' $? — no start marker, no polling	Dual start+end markers polled via capture-pane; output extracted between them
No reconnect logic — connection loss kills the session	Auto-reconnects on next command; keepalive every 30 s
No file transfer	SFTP: upload-file, download-file, write-remote-file
No port forwarding	forward-port / stop-forward via ssh2 forwardOut

New tools added

Tool	Purpose
setup-tmux	(Re)initialize tmux on an existing session
upload-file	Upload local file to remote via SFTP
download-file	Download remote file to local via SFTP
write-remote-file	Write text content directly via SFTP — no shell, no quoting issues, no heredoc
forward-port	Forward a local TCP port to a remote host:port
stop-forward	Stop a port forward tunnel

Reliability fixes

Issue	Root cause	Fix
Captured output contained entire pane history	End marker regex required a preceding \n; commands without trailing newline caused marker detection to fail → 30 s timeout → full pane returned as fallback	Regex changed to `endMarker(\d+)(?:\n
Long sessions accumulated large scrollback, slowing polling	capture-pane -S -1000 scanned 1000 lines on every poll	tmux clear-history before each command + window reduced to -S -200
heredoc (<< EOF) hung the session	tmux waits for EOF input that never arrives	Detected and rejected with a helpful error
exit code -1 was indistinguishable from a real command failure	Timeout and true failure both returned the same code	Timeout now returns [tmux capture timed out — command may still be running]

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Installation

npm install -g agent-ssh-mcp

Or run without installing:

npx agent-ssh-mcp

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MCP Client Configuration

Add to your MCP client config (Claude Desktop, Claude Code, Cursor, etc.):

{
  "mcpServers": {
    "ssh": {
      "command": "npx",
      "args": ["agent-ssh-mcp"]
    }
  }
}

Claude Desktop — ~/Library/Application Support/Claude/claude_desktop_config.json (macOS) or %APPDATA%\Claude\claude_desktop_config.json (Windows)

Claude Code / VS Code — .vscode/settings.json:

{
  "claude.mcpServers": {
    "ssh": { "command": "npx", "args": ["agent-ssh-mcp"] }
  }
}

Cursor — ~/Library/Application Support/Cursor/mcp.json (macOS)

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Host Configuration

Hosts are stored in ~/.ssh-mcp/hosts.json, created automatically on first use.

Add a host

{
  "tool": "add-host",
  "host_id": "my-server",
  "host": "1.2.3.4",
  "port": 22,
  "username": "root",
  "password": "optional",
  "keyPath": "~/.ssh/id_rsa"
}

Authentication priority: password → private key → SSH agent (SSH_AUTH_SOCK).

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Tools Reference

Session lifecycle

Tool	Parameters	Description
add-host	host_id, host, port, username, password?, keyPath?	Save SSH host config
list-hosts	—	List all saved hosts
edit-host	host_id + any field to change	Update host config
remove-host	host_id	Delete host config
start-session	host_id, sessionId?	Connect and auto-initialize tmux
list-sessions	—	Show active sessions with uptime
close-session	sessionId	Disconnect and clean up
setup-tmux	session_id	(Re)initialize tmux on an existing session

Command execution

Tool	Parameters	Description
exec	session_id, command	Run a command; auto-routes through tmux when available

Note: Do not use tmux send-keys manually — exec handles tmux routing automatically.

Avoid heredoc syntax (<< EOF). Use write-remote-file instead.

File transfer

Tool	Parameters	Description
upload-file	session_id, local_path, remote_path	Upload local file via SFTP (preferred for large/binary files)
download-file	session_id, remote_path, local_path	Download remote file via SFTP
write-remote-file	session_id, remote_path, content	Write text content directly via SFTP — handles special characters, no shell quoting issues

Port forwarding

Tool	Parameters	Description
forward-port	session_id, local_port, remote_host, remote_port, tunnel_id?	Forward 127.0.0.1:<local_port> → <remote_host>:<remote_port>
stop-forward	tunnel_id	Stop a port forward tunnel

Example — access a remote PostgreSQL locally:

{
  "tool": "forward-port",
  "session_id": "my-session",
  "local_port": 15432,
  "remote_host": "127.0.0.1",
  "remote_port": 5432
}

Then connect to postgresql://user:[email protected]:15432/db.

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Typical Agent Workflow

1. add-host       → save target server
2. start-session  → SSH connect + tmux init (returns session_id)
3. exec           → run commands (output is clean, no scrollback pollution)
4. write-remote-file / upload-file → write files reliably
5. forward-port   → expose remote services locally if needed
6. close-session  → clean up

Sessions auto-close after 2 hours of inactivity.

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tmux Observability

Every command is executed inside a tmux session named ai. You (or the user) can attach to watch in real time:

ssh root@<host>
tmux attach -t ai

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Building from Source

git clone https://github.com/xcdd/Agent-SSH-MCP
cd Agent-SSH-MCP
npm install
npm run build

Run tests:

npm test

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Security Notes

• ~/.ssh-mcp/hosts.json may contain passwords — treat it as sensitive (chmod 600).
• Prefer key-based or SSH agent authentication.
• Sessions inherit all privileges of the SSH user.

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License

MIT — see LICENSE.

Original work © 2025 Justin Fry. Modifications © 2026 xcdd.