Supercli MCP Development

Work on MCP (Model Context Protocol) features in supercli including adapter implementation, SSE streaming support, and server integration.

MCP Adapter Architecture

The MCP adapter (cli/adapters/mcp.js) supports multiple transport modes:

Transport Modes

1. HTTP/SSE MCP: HTTP-based MCP servers with SSE streaming
2. Stdio MCP with Daemon: Local stdio MCP servers routed through daemon
3. Stdio MCP Direct: Direct stdio calls (may have compatibility issues)

Key Components

• execute(): Main entry point, routes to appropriate transport
• callHttpMcpTool(): HTTP/SSE MCP handler with JSON-RPC support
• parseSseResponse(): SSE event parser
• callStdioTool(): Direct stdio execution
• stdioCallToolJsonRpc(): Stdio JSON-RPC protocol handler
• callDaemonTool(): Daemon-routed stdio calls

HTTP/SSE Implementation

Request Format

Uses JSON-RPC 2.0 format for HTTP MCP calls:

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "name": toolName,
    "arguments": input
  },
  "id": 1
}

Headers

Must include both content types for SSE negotiation:

{
  "Content-Type": "application/json",
  "Accept": "text/event-stream, application/json"
}

SSE Response Parsing

Parses Server-Sent Events format:

• Lines starting with event: define event type
• Lines starting with data: contain event data
• Empty lines terminate events
• Accumulates chunks and returns final result

Auto-detection

Automatically detects SSE responses via Content-Type header and falls back to JSON if not SSE.

Stdio MCP with Daemon

Configuration

{
  "adapterConfig": {
    "server": "mcp-server-name",
    "tool": "tool-name",
    "stateful": true,
    "timeout_ms": 60000
  }
}

Daemon Client

• File: cli/mcp-daemon-client.js
• Functions: callDaemonTool(), listDaemonTools()
• Maintains persistent sessions for stateful MCP servers
• Daemon runs on CLI side (not server) - starts on-demand when first command with stateful: true is executed via CLI
• Runs as detached background process with Unix socket at ~/.supercli/mcp-daemon.sock
• Persists across command executions to maintain MCP server sessions
• Better for long-running stdio MCP servers

Daemon Lifecycle:

• Auto-starts on first CLI command execution (checks socket, spawns daemon if not running)
• Server UI only stores configuration; CLI syncs and executes
• Manual control: supercli mcp daemon start/stop/status
• Detached process (unref) - doesn't block CLI
• 5-second startup timeout with retry checks

mcp-proxy Integration

What is mcp-proxy?

Transforms stdio MCP servers into HTTP/SSE endpoints. Useful for:

• Exposing local stdio MCPs over HTTP
• Testing MCP tools via HTTP clients
• Bridging stdio to SSE transport

Usage Pattern

# Start mcp-proxy
npx -y mcp-proxy --port 3002 -- npx -y @andredezzy/deep-directory-tree-mcp

# Add to supercli
supercli server mcp add '{"name":"deep-tree","url":"http://localhost:3002"}'

# Create command
supercli server commands add '{"namespace":"tree","resource":"deep","action":"list","adapter":"mcp","adapterConfig":{"url":"http://localhost:3002","tool":"get_deep_directory_tree"}}'

# Sync and use
supercli sync
supercli tree deep list --path /some/dir --depth 3

mcp-proxy Options

• --port: Port to listen on (default: 8080)
• --streamEndpoint: HTTP endpoint path (default: /mcp)
• --stateless: Disable session management
• --sseEndpoint: SSE endpoint path (default: /sse)

Server-Side MCP Management

Server Routes

• POST /api/mcp: Add MCP server
• GET /api/mcp: List MCP servers
• DELETE /api/mcp/:name: Remove MCP server

MCP Server Entry Format

{
  "name": "server-name",
  "url": "http://localhost:3002",
  "command": "npx -y @package",
  "args": ["--arg1", "--arg2"],
  "stateful": true,
  "timeout_ms": 60000,
  "headers": {},
  "env": {}
}

Server UI

• /mcp: MCP server management UI
• Add/remove servers
• View server status
• Test MCP tools

Client-Side MCP Usage

Command Configuration

{
  "namespace": "mcp",
  "resource": "server",
  "action": "tool",
  "adapter": "mcp",
  "adapterConfig": {
    "server": "mcp-server-name",
    "tool": "tool-name",
    "stateful": true
  }
}

Argument Passing

Use space syntax for CLI arguments:

• ✅ supercli tree deep list --path /dir --depth 2
• ❌ supercli tree deep list --path=/dir --depth=2

The supercli argument parser treats --key=value as a boolean flag with key=key=value, not as a key-value pair.

Testing MCP Integration

Test with mcp-proxy

# Start proxy
npx -y mcp-proxy --port 3002 -- npx -y @andredezzy/deep-directory-tree-mcp

# List tools
curl http://localhost:3002/tool -X POST \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream, application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/list","id":1}'

# Call tool
curl http://localhost:3002/tool -X POST \
  -H "Content-Type: application/json" \
  -H "Accept: text/event-stream, application/json" \
  -d '{"jsonrpc":"2.0","method":"tools/call","params":{"name":"tool-name","arguments":{}},"id":1}'

Test with Daemon

# Test daemon connection
node cli/mcp-daemon-client.js

# List tools via daemon
# (daemon client handles this internally)

Common Issues

"Not Acceptable: Client must accept both application/json and text/event-stream"

Cause: mcp-proxy requires SSE Accept header.

Fix: Ensure MCP adapter sends Accept: text/event-stream, application/json.

"Parse error: Invalid JSON-RPC message"

Cause: Wrong request format for HTTP MCP.

Fix: Use JSON-RPC 2.0 format with jsonrpc, method, params, and id fields.

"Tool not found"

Cause: Incorrect tool name or tool not exposed by MCP server.

Fix: Use tools/list method to discover available tool names.

"Input validation error"

Cause: Arguments not passed correctly or in wrong format.

Fix: Use space syntax (--key value) and verify argument schema matches tool expectations.

File Locations

• MCP Adapter: cli/adapters/mcp.js
• Daemon Client: cli/mcp-daemon-client.js
• Stdio JSON-RPC: cli/mcp-stdio-jsonrpc.js
• Server MCP Routes: server/routes/mcp.js
• Server MCP Service: server/services/mcpService.js

Development Workflow

1. Implement MCP adapter changes
2. Test with local stdio MCP or mcp-proxy
3. Update docs/server.md with new features
4. Update supercli-cli-admin-cheatsheet skill
5. Test via CLI commands
6. Verify server UI integration

Future Enhancements

• Streaming output: Implement --stream flag for incremental SSE output
• Session management: Add automatic session ID handling for stateful HTTP MCP
• Tool discovery: Auto-discover tools from MCP servers
• Schema validation: Validate arguments against tool input schemas