feat: add support for mcp server instructions (#579)

* feat: add support for mcp server instructions

Signed-off-by: Calum Murray <[email protected]>

* test: verify mcp server instructions set properly

Signed-off-by: Calum Murray <[email protected]>

---------

Signed-off-by: Calum Murray <[email protected]>

Author: Cali0707

pkg/config/config.go

@@ -81,6 +81,10 @@ type StaticConfig struct {
 	promptsDefined  bool           // Internal: tracks if prompts were defined in config
 	promptsMetadata toml.MetaData  // Internal: metadata for prompts decoding
 
+	// Server instructions to be provided by the MCP server to the MCP client
+	// This can be used to provide specific instructions on how the client should use the server
+	ServerInstructions string `toml:"server_instructions,omitempty"`
+
 	// Internal: parsed provider configs (not exposed to TOML package)
 	parsedClusterProviderConfigs map[string]configapi.Extended
 	// Internal: parsed toolset configs (not exposed to TOML package)

pkg/mcp/mcp.go

@@ -82,6 +82,7 @@ func NewServer(configuration Configuration) (*Server, error) {
 				HasResources: false,
 				HasPrompts:   true,
 				HasTools:     true,
+				Instructions: configuration.ServerInstructions,
 			}),
 	}
 

pkg/mcp/mcp_test.go

@@ -1,11 +1,14 @@
 package mcp
 
 import (
+	"context"
 	"net/http"
+	"net/http/httptest"
 	"sync"
 	"testing"
 
 	"github.com/containers/kubernetes-mcp-server/internal/test"
+	"github.com/mark3labs/mcp-go/client"
 	"github.com/mark3labs/mcp-go/client/transport"
 	"github.com/stretchr/testify/suite"
 )
@@ -97,3 +100,72 @@ func (s *McpHeadersSuite) TestAuthorizationHeaderPropagation() {
 func TestMcpHeaders(t *testing.T) {
 	suite.Run(t, new(McpHeadersSuite))
 }
+
+type ServerInstructionsSuite struct {
+	BaseMcpSuite
+	mockServer *test.MockServer
+}
+
+func (s *ServerInstructionsSuite) SetupTest() {
+	s.BaseMcpSuite.SetupTest()
+	s.mockServer = test.NewMockServer()
+	s.mockServer.Handle(&test.DiscoveryClientHandler{})
+	s.Cfg.KubeConfig = s.mockServer.KubeconfigFile(s.T())
+}
+
+func (s *ServerInstructionsSuite) TearDownTest() {
+	s.BaseMcpSuite.TearDownTest()
+	if s.mockServer != nil {
+		s.mockServer.Close()
+	}
+}
+
+func (s *ServerInstructionsSuite) TestServerInstructions() {
+	s.Run("returns empty instructions when not configured", func() {
+		s.Cfg.ServerInstructions = ""
+		mcpServer, err := NewServer(Configuration{StaticConfig: s.Cfg})
+		s.Require().NoError(err)
+		s.T().Cleanup(mcpServer.Close)
+
+		testServer := httptest.NewServer(mcpServer.ServeHTTP())
+		s.T().Cleanup(testServer.Close)
+
+		mcpClient, err := client.NewStreamableHttpClient(testServer.URL+"/mcp", transport.WithContinuousListening())
+		s.Require().NoError(err)
+		s.T().Cleanup(func() { _ = mcpClient.Close() })
+
+		err = mcpClient.Start(context.Background())
+		s.Require().NoError(err)
+
+		result, err := mcpClient.Initialize(context.Background(), test.McpInitRequest())
+		s.Require().NoError(err)
+		s.Empty(result.Instructions, "instructions should be empty when not configured")
+	})
+
+	s.Run("returns configured instructions", func() {
+		expectedInstructions := "Always use YAML output format for kubectl commands."
+		s.Cfg.ServerInstructions = expectedInstructions
+
+		mcpServer, err := NewServer(Configuration{StaticConfig: s.Cfg})
+		s.Require().NoError(err)
+		s.T().Cleanup(mcpServer.Close)
+
+		testServer := httptest.NewServer(mcpServer.ServeHTTP())
+		s.T().Cleanup(testServer.Close)
+
+		mcpClient, err := client.NewStreamableHttpClient(testServer.URL+"/mcp", transport.WithContinuousListening())
+		s.Require().NoError(err)
+		s.T().Cleanup(func() { _ = mcpClient.Close() })
+
+		err = mcpClient.Start(context.Background())
+		s.Require().NoError(err)
+
+		result, err := mcpClient.Initialize(context.Background(), test.McpInitRequest())
+		s.Require().NoError(err)
+		s.Equal(expectedInstructions, result.Instructions, "instructions should match configured value")
+	})
+}
+
+func TestServerInstructions(t *testing.T) {
+	suite.Run(t, new(ServerInstructionsSuite))
+}