feat: Add CSV output format for default list tools under insiders mode

cmd/github-mcp-server/main.go

@@ -126,6 +126,13 @@ var (
 				}
 			}
 
+			var enabledFeatures []string
+			if viper.IsSet("features") {
+				if err := viper.UnmarshalKey("features", &enabledFeatures); err != nil {
+					return fmt.Errorf("failed to unmarshal features: %w", err)
+				}
+			}
+
 			ttl := viper.GetDuration("repo-access-cache-ttl")
 			httpConfig := ghhttp.ServerConfig{
 				Version:              version,
@@ -144,6 +151,7 @@ var (
 				EnabledToolsets:      enabledToolsets,
 				EnabledTools:         enabledTools,
 				ExcludeTools:         excludeTools,
+				EnabledFeatures:      enabledFeatures,
 				InsidersMode:         viper.GetBool("insiders"),
 			}
 

docs/insiders-features.md

@@ -42,3 +42,28 @@ MCP Apps requires a host that supports the [MCP Apps extension](https://modelcon
 
 - **VS Code Insiders** — enable via the `chat.mcp.apps.enabled` setting
 - **Visual Studio Code** — enable via the `chat.mcp.apps.enabled` setting
+
+---
+
+## CSV output for list tools
+
+CSV output mode returns supported list tool responses as CSV instead of JSON. This is intended to reduce response context for agents when scanning or summarising lists of GitHub data.
+
+CSV output applies only to tools in default toolsets whose names start with `list_`, such as `list_issues`, `list_pull_requests`, `list_commits`, and `list_branches`. It does not add new tools or expose a tool argument for selecting the format; the server controls the response format through the Insiders feature flag.
+
+### Format
+
+- Nested objects are flattened into dot-notation columns, for example `user.login`, `category.name`, or `head.ref`.
+- Arrays are represented as compact single-cell values joined with `;`.
+- `body` fields are whitespace-normalized so multiline Markdown does not expand a list response into many output lines.
+- Response metadata present in wrapped responses, such as `pageInfo.*` and `totalCount`, is emitted as `#`-prefixed lines before the CSV rows, followed by a blank line. Tools that return a root JSON array do not include metadata preamble lines.
+
+### Enabling CSV output
+
+CSV output is enabled by Insiders Mode. For local development, it can also be enabled explicitly with the `csv_output` feature flag:
+
+```bash
+github-mcp-server stdio --features csv_output
+```
+
+Because this changes list tool response shape, clients that require JSON list responses should avoid enabling this feature.

internal/ghmcp/server.go

@@ -143,7 +143,6 @@ func NewStdioMCPServer(ctx context.Context, cfg github.MCPServerConfig) (*mcp.Se
 		cfg.Translator,
 		github.FeatureFlags{
 			LockdownMode: cfg.LockdownMode,
-			InsidersMode: cfg.InsidersMode,
 		},
 		cfg.ContentWindowSize,
 		featureChecker,
@@ -229,7 +228,7 @@ type StdioServerConfig struct {
 	// LockdownMode indicates if we should enable lockdown mode
 	LockdownMode bool
 
-	// InsidersMode indicates if we should enable experimental features
+	// InsidersMode expands to the curated set of feature flags enabled for insiders.
 	InsidersMode bool
 
 	// ExcludeTools is a list of tool names to disable regardless of other settings.
@@ -345,7 +344,7 @@ func RunStdioServer(cfg StdioServerConfig) error {
 
 // createFeatureChecker returns a FeatureFlagChecker that resolves features
 // using the centralized ResolveFeatureFlags function. For the local server,
-// features are resolved once at startup from --features CLI flag + insiders mode.
+// features are resolved once at startup from --features CLI flag and insiders mode.
 func createFeatureChecker(enabledFeatures []string, insidersMode bool) inventory.FeatureFlagChecker {
 	featureSet := github.ResolveFeatureFlags(enabledFeatures, insidersMode)
 	return func(_ context.Context, flagName string) (bool, error) {
@@ -372,9 +371,6 @@ func addUserAgentsMiddleware(cfg github.MCPServerConfig, restUATransp *transport
 				message.Params.ClientInfo.Name,
 				message.Params.ClientInfo.Version,
 			)
-			if cfg.InsidersMode {
-				userAgent += " (insiders)"
-			}
 
 			restUATransp.Agent = userAgent
 

pkg/github/context_tools.go

@@ -106,7 +106,7 @@ func GetMe(t translations.TranslationHelperFunc) inventory.ServerTool {
 			}
 
 			result := MarshalledTextResult(minimalUser)
-			if deps.GetFlags(ctx).InsidersMode {
+			if deps.IsFeatureEnabled(ctx, FeatureFlagIFCLabels) {
 				if result.Meta == nil {
 					result.Meta = mcp.Meta{}
 				}

pkg/github/context_tools_test.go

@@ -139,7 +139,7 @@ func Test_GetMe(t *testing.T) {
 	}
 }
 
-func Test_GetMe_IFC_InsidersMode(t *testing.T) {
+func Test_GetMe_IFC_FeatureFlag(t *testing.T) {
 	t.Parallel()
 
 	serverTool := GetMe(translations.NullTranslationHelper)
@@ -153,34 +153,41 @@ func Test_GetMe_IFC_InsidersMode(t *testing.T) {
 		GetUser: mockResponse(t, http.StatusOK, mockUser),
 	})
 
-	t.Run("insiders mode disabled omits ifc label from result meta", func(t *testing.T) {
-		deps := BaseDeps{
-			Client: mustNewGHClient(t, mockedHTTPClient),
-			Flags:  FeatureFlags{InsidersMode: false},
-		}
+	depsWithIFCFeature := func(enabled bool) *BaseDeps {
+		return NewBaseDeps(
+			mustNewGHClient(t, mockedHTTPClient), nil, nil, nil,
+			translations.NullTranslationHelper,
+			FeatureFlags{},
+			0,
+			func(_ context.Context, flagName string) (bool, error) {
+				return flagName == FeatureFlagIFCLabels && enabled, nil
+			},
+			stubExporters(),
+		)
+	}
+
+	t.Run("feature disabled omits ifc label from result meta", func(t *testing.T) {
+		deps := depsWithIFCFeature(false)
 		handler := serverTool.Handler(deps)
 
 		request := createMCPRequest(map[string]any{})
 		result, err := handler(ContextWithDeps(context.Background(), deps), &request)
 		require.NoError(t, err)
 		require.False(t, result.IsError)
 
-		assert.Nil(t, result.Meta, "result meta should be nil when insiders mode is disabled")
+		assert.Nil(t, result.Meta, "result meta should be nil when IFC labels are disabled")
 	})
 
-	t.Run("insiders mode enabled includes ifc label in result meta", func(t *testing.T) {
-		deps := BaseDeps{
-			Client: mustNewGHClient(t, mockedHTTPClient),
-			Flags:  FeatureFlags{InsidersMode: true},
-		}
+	t.Run("feature enabled includes ifc label in result meta", func(t *testing.T) {
+		deps := depsWithIFCFeature(true)
 		handler := serverTool.Handler(deps)
 
 		request := createMCPRequest(map[string]any{})
 		result, err := handler(ContextWithDeps(context.Background(), deps), &request)
 		require.NoError(t, err)
 		require.False(t, result.IsError)
 
-		require.NotNil(t, result.Meta, "result meta should be set when insiders mode is enabled")
+		require.NotNil(t, result.Meta, "result meta should be set when IFC labels are enabled")
 		ifcLabel, ok := result.Meta["ifc"]
 		require.True(t, ok, "result meta should contain ifc key")