diff --git a/internal/router/router.go b/internal/router/router.go
index e98a5b5..8bb5bd4 100644
--- a/internal/router/router.go
+++ b/internal/router/router.go
@@ -9,6 +9,7 @@ import (
 	"bookhoard/internal/sync"
 	"log"
 	"net/http"
+	"strings"
 	"time"
 
 	"github.com/go-playground/validator/v10"
@@ -85,11 +86,44 @@ func createJWTMiddleware(cfg *Config) echo.MiddlewareFunc {
 			})
 		},
 		ErrorHandler: func(c echo.Context, err error) error {
-			return c.JSON(http.StatusUnauthorized, map[string]string{"error": err.Error()})
+			// Check if this is a page request (browser navigation)
+			if wantsHTML(c.Request().Header) {
+				// Page request → Redirect to login with message
+				loginURL := "/login?session=expired"
+				return c.Redirect(http.StatusFound, loginURL)
+			}
+
+			// API request → Return JSON error
+			return c.JSON(http.StatusUnauthorized, map[string]string{
+				"error":   "session_expired",
+				"message": "Your session has expired. Please log in again.",
+			})
 		},
 	})
 }
 
+// wantsHTML determines if the request expects HTML response
+func wantsHTML(header http.Header) bool {
+	// Check Accept header
+	accept := header.Get("Accept")
+	if accept != "" && (accept == "text/html" || strings.Contains(accept, "text/html")) {
+		return true
+	}
+
+	// Check HTMX request
+	if header.Get("HX-Request") == "true" {
+		return true
+	}
+
+	// Check for AJAX requests (should get JSON)
+	if header.Get("X-Requested-With") == "XMLHttpRequest" {
+		return false
+	}
+
+	// Default to JSON for API routes
+	return false
+}
+
 // RegisterRoutes registers all application routes
 func RegisterRoutes(cfg *Config) *handlers.Handler {
 	e := cfg.Echo