Prevent servers without tools from being added/running (#173)

Author: peteski22

cmd/add.go

@@ -283,6 +283,9 @@ func parseServerEntry(pkg packages.Server, opts serverEntryOptions) (config.Serv
 	if err != nil {
 		return config.ServerEntry{}, fmt.Errorf("error matching requested tools: %w", err)
 	}
+	if len(requestedTools) == 0 {
+		return config.ServerEntry{}, fmt.Errorf("tools not available")
+	}
 
 	selectedRuntime, err := selectRuntime(pkg.Installations, opts.Runtime, opts.SupportedRuntimes)
 	if err != nil {

cmd/add_test.go

@@ -677,6 +677,40 @@ func TestParseServerEntry(t *testing.T) {
 			isErrorExpected:      true,
 			expectedErrorMessage: "installation server name is missing for runtime 'docker'",
 		},
+		{
+			name: "server with no tools available",
+			installations: map[runtime.Runtime]packages.Installation{
+				runtime.UVX: {
+					Package:     "mcp-server-no-tools",
+					Recommended: true,
+				},
+			},
+			supportedRuntimes:    []runtime.Runtime{runtime.UVX},
+			pkgName:              "no-tools",
+			pkgID:                "no-tools",
+			availableTools:       []string{}, // No tools available
+			requestedTools:       []string{},
+			arguments:            packages.Arguments{},
+			isErrorExpected:      true,
+			expectedErrorMessage: "tools not available",
+		},
+		{
+			name: "server with requested tools not available",
+			installations: map[runtime.Runtime]packages.Installation{
+				runtime.UVX: {
+					Package:     "mcp-server-limited",
+					Recommended: true,
+				},
+			},
+			supportedRuntimes:    []runtime.Runtime{runtime.UVX},
+			pkgName:              "limited",
+			pkgID:                "limited",
+			availableTools:       []string{"toolA", "toolB"},
+			requestedTools:       []string{"toolC", "toolD"}, // Requesting unavailable tools
+			arguments:            packages.Arguments{},
+			isErrorExpected:      true,
+			expectedErrorMessage: "error matching requested tools: none of the requested values were found",
+		},
 		{
 			name: "requested tool not found",
 			installations: map[runtime.Runtime]packages.Installation{

cmd/config/tools/remove.go

@@ -76,6 +76,12 @@ func (c *RemoveCmd) run(cmd *cobra.Command, args []string) error {
 			}
 		}
 
+		// Validate that at least one tool remains.
+		if len(srv.Tools) == 0 {
+			return fmt.Errorf("cannot remove all tools from server '%s'\n"+
+				"To remove the server instead use: mcpd remove %s", serverName, serverName)
+		}
+
 		// Update server in config by removing and re-adding.
 		err = cfg.RemoveServer(serverName)
 		if err != nil {

cmd/config/tools/remove_test.go

@@ -0,0 +1,128 @@
+package tools
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"github.com/mozilla-ai/mcpd/v2/internal/cmd"
+	cmdopts "github.com/mozilla-ai/mcpd/v2/internal/cmd/options"
+	"github.com/mozilla-ai/mcpd/v2/internal/config"
+)
+
+type mockConfigForRemove struct {
+	servers   []config.ServerEntry
+	addErr    error
+	removeErr error
+}
+
+func (m *mockConfigForRemove) AddServer(entry config.ServerEntry) error {
+	if m.addErr != nil {
+		return m.addErr
+	}
+	m.servers = append(m.servers, entry)
+	return nil
+}
+
+func (m *mockConfigForRemove) RemoveServer(name string) error {
+	if m.removeErr != nil {
+		return m.removeErr
+	}
+	for i, s := range m.servers {
+		if s.Name == name {
+			m.servers = append(m.servers[:i], m.servers[i+1:]...)
+			return nil
+		}
+	}
+	return nil
+}
+
+func (m *mockConfigForRemove) ListServers() []config.ServerEntry {
+	return m.servers
+}
+
+func (m *mockConfigForRemove) SaveConfig() error {
+	return nil
+}
+
+type mockLoaderForRemove struct {
+	cfg *mockConfigForRemove
+	err error
+}
+
+func (m *mockLoaderForRemove) Load(_ string) (config.Modifier, error) {
+	return m.cfg, m.err
+}
+
+func TestRemoveCmd_RemoveAllTools(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name          string
+		serverName    string
+		initialTools  []string
+		toolsToRemove []string
+		expectedError string
+	}{
+		{
+			name:          "removing all tools should fail",
+			serverName:    "test-server",
+			initialTools:  []string{"tool1", "tool2"},
+			toolsToRemove: []string{"tool1", "tool2"},
+			expectedError: "cannot remove all tools from server 'test-server'\nTo remove the server instead use: mcpd remove test-server",
+		},
+		{
+			name:          "removing last tool should fail",
+			serverName:    "test-server",
+			initialTools:  []string{"tool1"},
+			toolsToRemove: []string{"tool1"},
+			expectedError: "cannot remove all tools from server 'test-server'\nTo remove the server instead use: mcpd remove test-server",
+		},
+		{
+			name:          "removing some tools should succeed",
+			serverName:    "test-server",
+			initialTools:  []string{"tool1", "tool2", "tool3"},
+			toolsToRemove: []string{"tool1", "tool2"},
+			expectedError: "",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			cfg := &mockConfigForRemove{
+				servers: []config.ServerEntry{
+					{
+						Name:  tc.serverName,
+						Tools: tc.initialTools,
+					},
+				},
+			}
+
+			loader := &mockLoaderForRemove{cfg: cfg}
+			baseCmd := &cmd.BaseCmd{}
+
+			removeCmd, err := NewRemoveCmd(baseCmd, cmdopts.WithConfigLoader(loader))
+			require.NoError(t, err)
+
+			// Prepare arguments: server-name followed by tools to remove.
+			args := append([]string{tc.serverName}, tc.toolsToRemove...)
+
+			var out bytes.Buffer
+			removeCmd.SetOut(&out)
+			removeCmd.SetErr(&out)
+
+			err = removeCmd.RunE(removeCmd, args)
+
+			if tc.expectedError != "" {
+				require.EqualError(t, err, tc.expectedError)
+			} else {
+				require.NoError(t, err)
+				// Verify some tools remain.
+				require.Greater(t, len(cfg.servers[0].Tools), 0)
+			}
+		})
+	}
+}

docs/configuration.md

@@ -201,6 +201,7 @@ The reload process maintains strict consistency - any error causes the daemon to
 
 - **Configuration errors**: Invalid configuration files or loading failures cause the daemon to exit
 - **Validation errors**: Invalid server configurations cause the daemon to exit  
+- **No tools configured**: If a server configuration has no tools (empty tools list or manually removed from config), the daemon will exit with an error
 - **Server operation failures**: Any failure to start, stop, or restart a server causes the daemon to exit
 
 This ensures the daemon never runs in an inconsistent or partially-failed state, matching the behavior during initial startup where any server failure prevents the daemon from running.

internal/daemon/daemon.go

@@ -158,7 +158,17 @@ func (d *Daemon) startMCPServers(ctx context.Context) error {
 	return nil
 }
 
+// startMCPServer starts a single MCP server and registers it with the daemon.
+// It validates that the server has tools and a supported runtime before initializing.
 func (d *Daemon) startMCPServer(ctx context.Context, server runtime.Server) error {
+	// Validate that the server has tools configured.
+	if len(server.Tools) == 0 {
+		return fmt.Errorf(
+			"server '%s' has no tools configured - MCP servers require at least one tool to function",
+			server.Name(),
+		)
+	}
+
 	runtimeBinary := server.Runtime()
 	if _, supported := d.supportedRuntimes[runtime.Runtime(runtimeBinary)]; !supported {
 		return fmt.Errorf(

internal/daemon/daemon_test.go

@@ -862,6 +862,67 @@ func TestDaemon_CloseClientWithTimeout_Direct(t *testing.T) {
 	}
 }
 
+// TestDaemon_StartMCPServer_NoTools tests that servers without tools are rejected
+func TestDaemon_StartMCPServer_NoTools(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name          string
+		serverName    string
+		tools         []string
+		expectedError string
+	}{
+		{
+			name:          "server with no tools should fail",
+			serverName:    "test-no-tools",
+			tools:         []string{},
+			expectedError: "server 'test-no-tools' has no tools configured - MCP servers require at least one tool to function",
+		},
+		{
+			name:          "server with empty tools list should fail",
+			serverName:    "test-empty-tools",
+			tools:         []string{},
+			expectedError: "server 'test-empty-tools' has no tools configured - MCP servers require at least one tool to function",
+		},
+	}
+
+	for _, tc := range tests {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+			t.Cleanup(cancel)
+
+			logger := hclog.NewNullLogger()
+
+			// Create a daemon with a dummy server to satisfy validation.
+			dummyServer := runtime.Server{
+				ServerEntry: config.ServerEntry{
+					Name:    "dummy",
+					Package: "uvx::dummy",
+				},
+			}
+			deps, err := NewDependencies(logger, ":8085", []runtime.Server{dummyServer})
+			require.NoError(t, err)
+			daemon, err := NewDaemon(deps)
+			require.NoError(t, err)
+
+			// Create server with specified tools.
+			server := runtime.Server{
+				ServerEntry: config.ServerEntry{
+					Name:    tc.serverName,
+					Package: "uvx::test-package",
+					Tools:   tc.tools,
+				},
+				ServerExecutionContext: configcontext.ServerExecutionContext{},
+			}
+
+			err = daemon.startMCPServer(ctx, server)
+			require.EqualError(t, err, tc.expectedError)
+		})
+	}
+}
+
 // TestDaemon_CloseClientWithTimeout_ReturnValue tests the return value behavior of closeClientWithTimeout
 func TestDaemon_CloseClientWithTimeout_ReturnValue(t *testing.T) {
 	t.Parallel()