diff --git a/components/backend/handlers/gitlab_auth.go b/components/backend/handlers/gitlab_auth.go
index bb47a1f57..7b165e68a 100644
--- a/components/backend/handlers/gitlab_auth.go
+++ b/components/backend/handlers/gitlab_auth.go
@@ -4,6 +4,7 @@ import (
 	"context"
 	"encoding/json"
 	"fmt"
+	"net"
 	"net/http"
 	"net/url"
 	"strings"
@@ -18,6 +19,8 @@ import (
 	"ambient-code-backend/gitlab"
 )
 
+var validateGitLabConnectivityFn = validateGitLabConnectivity
+
 // GitLabAuthHandler handles GitLab authentication endpoints
 type GitLabAuthHandler struct {
 	connectionManager *gitlab.ConnectionManager
@@ -115,6 +118,40 @@ func validateGitLabInput(instanceURL, token string) error {
 	return nil
 }
 
+// validateGitLabConnectivity validates that the instance is resolvable and PAT can authenticate.
+func validateGitLabConnectivity(ctx context.Context, instanceURL, token string) error {
+	parsedURL, err := url.Parse(instanceURL)
+	if err != nil {
+		return fmt.Errorf("invalid instance URL format")
+	}
+
+	hostname := parsedURL.Hostname()
+	if hostname == "" {
+		return fmt.Errorf("instance URL must have a valid hostname")
+	}
+
+	resolveCtx, cancel := context.WithTimeout(ctx, 5*time.Second)
+	defer cancel()
+
+	addresses, err := net.DefaultResolver.LookupHost(resolveCtx, hostname)
+	if err != nil {
+		return fmt.Errorf("cannot resolve GitLab instance host '%s': %w", hostname, err)
+	}
+	if len(addresses) == 0 {
+		return fmt.Errorf("cannot resolve GitLab instance host '%s': no addresses returned", hostname)
+	}
+
+	valid, err := ValidateGitLabToken(ctx, token, instanceURL)
+	if err != nil {
+		return fmt.Errorf("failed to connect to GitLab API at %s: %w", instanceURL, err)
+	}
+	if !valid {
+		return fmt.Errorf("failed to authenticate with the provided Personal Access Token")
+	}
+
+	return nil
+}
+
 // ConnectGitLab handles POST /projects/:projectName/auth/gitlab/connect
 func (h *GitLabAuthHandler) ConnectGitLab(c *gin.Context) {
 	// Get project from URL parameter
@@ -410,6 +447,12 @@ func ConnectGitLabGlobal(c *gin.Context) {
 		return
 	}
 
+	// Validate connectivity/auth before storing credentials.
+	if err := validateGitLabConnectivityFn(c.Request.Context(), req.InstanceURL, req.PersonalAccessToken); err != nil {
+		c.JSON(http.StatusBadRequest, gin.H{"error": fmt.Sprintf("GitLab connectivity check failed: %v", err)})
+		return
+	}
+
 	// Store credentials at cluster level
 	creds := &GitLabCredentials{
 		UserID:      userID,
diff --git a/components/backend/handlers/gitlab_auth_test.go b/components/backend/handlers/gitlab_auth_test.go
index 1cbe2bb58..c110be234 100644
--- a/components/backend/handlers/gitlab_auth_test.go
+++ b/components/backend/handlers/gitlab_auth_test.go
@@ -22,16 +22,19 @@ import (
 
 var _ = Describe("GitLab Auth Handler", Label(test_constants.LabelUnit, test_constants.LabelHandlers, test_constants.LabelGitLabAuth), func() {
 	var (
-		httpUtils         *test_utils.HTTPTestUtils
-		k8sUtils          *test_utils.K8sTestUtils
-		originalNamespace string
-		testToken         string
+		httpUtils                          *test_utils.HTTPTestUtils
+		k8sUtils                           *test_utils.K8sTestUtils
+		originalNamespace                  string
+		originalValidateGitLabConnectivity func(context.Context, string, string) error
+		testToken                          string
 	)
 
 	BeforeEach(func() {
 		logger.Log("Setting up GitLab Auth Handler test")
 
 		originalNamespace = Namespace
+		originalValidateGitLabConnectivity = validateGitLabConnectivityFn
+		validateGitLabConnectivityFn = func(_ context.Context, _, _ string) error { return nil }
 
 		// Use centralized handler dependencies setup
 		k8sUtils = test_utils.NewK8sTestUtils(false, *config.TestNamespace)
@@ -67,6 +70,7 @@ var _ = Describe("GitLab Auth Handler", Label(test_constants.LabelUnit, test_con
 
 	AfterEach(func() {
 		Namespace = originalNamespace
+		validateGitLabConnectivityFn = originalValidateGitLabConnectivity
 
 		// Clean up created namespace (best-effort)
 		if k8sUtils != nil {
@@ -566,6 +570,46 @@ var _ = Describe("GitLab Auth Handler", Label(test_constants.LabelUnit, test_con
 
 			// Note: Global function K8s client validation tested at integration level
 			// Unit tests focus on specific handler logic
+
+			It("Should fail when GitLab hostname cannot be resolved", func() {
+				validateGitLabConnectivityFn = func(_ context.Context, _, _ string) error {
+					return fmt.Errorf("cannot resolve GitLab instance host 'gitlab.internal': lookup failed")
+				}
+
+				requestBody := map[string]interface{}{
+					"personalAccessToken": "valid_token_1234567890",
+					"instanceUrl":         "https://gitlab.internal",
+				}
+
+				context := httpUtils.CreateTestGinContext("POST", "/auth/gitlab/connect", requestBody)
+				httpUtils.SetAuthHeader(testToken)
+				httpUtils.SetUserContext("test-user", "Test User", "test@example.com")
+
+				ConnectGitLabGlobal(context)
+
+				httpUtils.AssertHTTPStatus(http.StatusBadRequest)
+				httpUtils.AssertErrorMessage("GitLab connectivity check failed: cannot resolve GitLab instance host 'gitlab.internal': lookup failed")
+			})
+
+			It("Should fail when GitLab PAT authentication fails", func() {
+				validateGitLabConnectivityFn = func(_ context.Context, _, _ string) error {
+					return fmt.Errorf("failed to authenticate with the provided Personal Access Token")
+				}
+
+				requestBody := map[string]interface{}{
+					"personalAccessToken": "valid_token_1234567890",
+					"instanceUrl":         "https://gitlab.com",
+				}
+
+				context := httpUtils.CreateTestGinContext("POST", "/auth/gitlab/connect", requestBody)
+				httpUtils.SetAuthHeader(testToken)
+				httpUtils.SetUserContext("test-user", "Test User", "test@example.com")
+
+				ConnectGitLabGlobal(context)
+
+				httpUtils.AssertHTTPStatus(http.StatusBadRequest)
+				httpUtils.AssertErrorMessage("GitLab connectivity check failed: failed to authenticate with the provided Personal Access Token")
+			})
 		})
 
 		Describe("GetGitLabStatusGlobal", func() {