Listen option is ignored unless config option is set explicitly

[stek29]

I've changed the listen option, but it only works if -c is passed explicitly.

$ <~/.mcpproxy/mcp_config.json jq -r .listen
127.0.0.1:12080

trying to start mcpproxy:

$ mcpproxy |& grep -e 'Starting HTTP' -e 'config'
2025-07-09 15:03:37	INFO	cobra@v1.9.1/command.go:1015	Log directory configured	{"path": "/Users/username/Library/Logs/mcpproxy", "os": "darwin", "standard": "macOS File System Programming Guide"}
2025-07-09 15:03:37	INFO	server/server.go:193	Status updated	{"phase": "Loading", "message": "Loading configuration and connecting to servers..."}
2025-07-09 15:03:37	INFO	server/server.go:196	Synchronizing servers from configuration (config as source of truth)
2025-07-09 15:03:37	INFO	server/server.go:196	Server synchronization completed	{"configured_servers": 0, "removed_servers": 0}
2025-07-09 15:03:37	INFO	tray/tray.go:156	Config file watcher initialized{path 15 0 /Users/username/.mcpproxy/mcp_config.json <nil>}
2025-07-09 15:03:37	INFO	server/server.go:483	Starting HTTP server	{"address": ":8080", "endpoints": ["/mcp", "/mcp/", "/v1/tool_code", "/v1/tool-code"]}
^C

notice how it started on default :8080

Now starting it with -c option, which points to default config file path which was loaded before:

$ mcpproxy -c ~/.mcpproxy/mcp_config.json |& grep -e 'Starting HTTP' -e 'config'
2025-07-09 15:04:06	INFO	cobra@v1.9.1/command.go:1015	Log directory configured	{"path": "/Users/username/Library/Logs/mcpproxy", "os": "darwin", "standard": "macOS File System Programming Guide"}
2025-07-09 15:04:06	INFO	server/server.go:193	Status updated	{"phase": "Loading", "message": "Loading configuration and connecting to servers..."}
2025-07-09 15:04:06	INFO	server/server.go:196	Synchronizing servers from configuration (config as source of truth)
2025-07-09 15:04:06	INFO	server/server.go:196	Server synchronization completed	{"configured_servers": 0, "removed_servers": 0}
2025-07-09 15:04:06	INFO	tray/tray.go:156	Config file watcher initialized{path 15 0 /Users/username/.mcpproxy/mcp_config.json <nil>}
2025-07-09 15:04:06	INFO	server/server.go:483	Starting HTTP server	{"address": "127.0.0.1:12080", "endpoints": ["/mcp", "/mcp/", "/v1/tool_code", "/v1/tool-code"]}

and this time it has started with expected listen address

[Dumbris]

Hi @stek29 ,

Thank you for filing this issue and providing such detailed reproduction steps! This was indeed a bug in the configuration loading logic, and it has now been fixed.

What was wrong

The issue was that mcpproxy without the -c flag was ignoring the listen setting from the config file due to viper's default values overwriting the loaded configuration.

The fix #20

The configuration loading logic has been updated to properly respect config file values when no explicit CLI flags are provided.

🔧 Port Configuration Guide

You can configure the listen port using any of these methods, in order of priority:

1. CLI parameter (highest priority)

   mcpproxy -l 127.0.0.1:9000
   # or
   mcpproxy --listen 127.0.0.1:9000

2. Config file (medium priority)

   {
     "listen": "127.0.0.1:12080",
     "data_dir": "/Users/user/.mcpproxy",
     ...
   }

3. Default port (lowest priority)

   :8080
   

Config file locations

mcpproxy automatically looks for mcp_config.json in:

• Current directory: ./mcp_config.json
• User data directory: ~/.mcpproxy/mcp_config.json

Verification

Your original test case now works correctly:

# This now uses 127.0.0.1:12080 from config file
$ mcpproxy --log-level=debug --tray=false
2025-07-15 17:45:40     INFO    server/server.go:483    Starting HTTP server    {"address": "127.0.0.1:12080", ...}

Thanks again for the detailed bug report! 🙏