{"record":{"id":"86e72c2194c27637","repo":"deepset-ai/haystack","slug":"invalid-template-for-output-output","errorCode":null,"errorMessage":"Invalid template for output: {output}","messagePattern":"Invalid template for output: (.+?)","errorType":"validation","errorClass":"ValueError","httpStatus":null,"severity":"error","filePath":"haystack/components/routers/conditional_router.py","lineNumber":532,"sourceCode":"                    raise ValueError(\n                        f\"Invalid template for condition: {condition_value!r} (type: {type(condition_value).__name__}).\"\n                        f\"Condition must be a string representing a valid Jinja2 template. \"\n                        f\"For example, use {str(condition_value)!r} instead of {condition_value!r}.\"\n                    )\n                raise ValueError(f\"Invalid template for condition: {condition_value}\")\n\n            # Only validate output as Jinja2 template when output_passthrough is False (default)\n            output_passthrough = route.get(\"output_passthrough\", False)\n            if not output_passthrough:\n                for output in outputs:\n                    if not self._validate_template(self._env, output):\n                        if not isinstance(output, str):\n                            raise ValueError(\n                                f\"Invalid template for output: {output!r} (type: {type(output).__name__}). \"\n                                f\"Output must be a string representing a valid Jinja2 template. \"\n                                f\"For example, use {str(output)!r} instead of {output!r}.\"\n                            )\n                        raise ValueError(f\"Invalid template for output: {output}\")\n\n    @staticmethod\n    def _extract_variables(env: Environment, templates: list[str]) -> set[str]:\n        \"\"\"\n        Extracts all variables from a list of Jinja template strings.\n\n        :param env: A Jinja environment.\n        :param templates: A list of Jinja template strings.\n        :returns: A set of variable names.\n        \"\"\"\n        variables = set()\n        for template in templates:\n            assigned_variables, template_variables = _extract_template_variables_and_assignments(\n                env=env, template=template\n            )\n            variables.update(template_variables - assigned_variables)\n        return variables\n","sourceCodeStart":514,"sourceCodeEnd":550,"githubUrl":"https://github.com/deepset-ai/haystack/blob/e318778c9bf60a1963e3b5f451359655dd696c30/haystack/components/routers/conditional_router.py#L514-L550","documentation":"This is the fallback ValueError raised in ConditionalRouter._validate_routes when the route 'output' is a string but still fails Jinja2 template validation (invalid Jinja syntax), while output_passthrough is False.","triggerScenarios":"A string 'output' containing malformed Jinja2 syntax, e.g. '{{ x ' (unclosed braces) or '{% if %}' without end tag.","commonSituations":"Hand-written templates with typos; templates built by concatenation that produce unbalanced {{ }} or {% %} blocks.","solutions":["Fix the Jinja2 syntax in the output template (close all {{ }} and {% %} blocks)","Validate the template with jinja2.Environment().parse(output) locally to see the syntax error","Ensure variables used are allowed; variable existence is not validated, only syntax"],"exampleFix":"# before\n{\"condition\": \"{{ ok }}\", \"output\": \"{{ result \", \"output_name\": \"out\", \"output_type\": str}\n# after\n{\"condition\": \"{{ ok }}\", \"output\": \"{{ result }}\", \"output_name\": \"out\", \"output_type\": str}","handlingStrategy":"validation","validationCode":"import jinja2\nenv = jinja2.Environment()\nfor r in routes:\n    if not r.get(\"output_passthrough\", False):\n        env.parse(r[\"output\"])  # raises TemplateSyntaxError on bad syntax","typeGuard":null,"tryCatchPattern":"try:\n    router = ConditionalRouter(routes=routes)\nexcept ValueError as e:\n    if \"Invalid template for output\" in str(e):\n        logging.error(\"Fix the Jinja2 syntax of the failing route output: %s\", e)\n        raise","preventionTips":["Validate templates with jinja2.Environment().parse() before constructing the router","Avoid building templates by string concatenation that can unbalance braces","Lint template strings in CI with jinja2 syntax checks"],"tags":["python","validation","jinja2","router"],"backgroundTag":"invalid-template","analyzedSha":"e318778c9bf60a1963e3b5f451359655dd696c30","analyzedAt":"2026-08-30T11:45:20.711Z","schemaVersion":2},"datasetVersion":"2026-08-30T13:17:10.514Z"}