diff --git a/app/main.py b/app/main.py
index 7e02612..16aa2ea 100644
--- a/app/main.py
+++ b/app/main.py
@@ -128,8 +128,10 @@ def create_app() -> FastAPI:
     )
 
     # Templates
+    import json as _json
     templates_dir = Path(__file__).parent / "templates"
     templates = Jinja2Templates(directory=str(templates_dir))
+    templates.env.filters["tojson"] = _json.dumps
 
     # Register UI routes (must come before API to avoid catch-all conflicts)
     from .ui.routes import router as ui_router, setup_templates