symfony/routing · error · RuntimeException

The container parameter

Error message

The container parameter "%s", used in the route configuration value "%s", must be a string or numeric, but it is of type "%s".

What it means

Route configuration values are built from container parameters; every matched %param% must resolve to a string or scalar so it can be cast. This error means the parameter resolved to a non-scalar type (array, null, object) and cannot be embedded in the route configuration string.

Solutions

1. Change the parameter to a scalar (string/int/bool) value in your config.
2. Reference a specific scalar element of the array parameter instead of the whole array.
3. Check config parsing: YAML values like 'key: [a, b]' become arrays; quote or restructure them.

Example fix

// before (config.yaml)
parameters:
  app_hosts: ['a.com', 'b.com']
# routes.yaml: host: '%app_hosts%'
// after
parameters:
  app_host: 'a.com'
# routes.yaml: host: '%app_host%'

$v = $container->getParameter($name);
if (!is_scalar($v) && null !== $v) {
    throw new LogicException("Parameter $name must be scalar for routing use.");
}

function isScalarParam(mixed $v): bool { return is_scalar($v) || null === $v; }

try { $url = $generator->generate($name, $params); } catch (RuntimeException $e) { // non-scalar parameter in route config
    $logger->error($e->getMessage());
}

When it happens

Trigger: Router::resolve finds %param% in a route value, paramFetcher returns an array/null/resource, and get_debug_type reports a non-scalar type.

Common situations: Defining a route default or host as an array parameter in config; a YAML parameter parsed as a list; a null parameter after failed env resolution.

Understand the failure class

Background: Type mismatch errors: IllegalArgumentException, TypeError and type guards across 150 open-source libraries — this error's family across 150 libraries.

Related errors

• Using "%% %%" is not allowed in routing configuration.
• The container parameter
• Unable to generate a URL for the named route
• Target route " " for alias " " does not exist.
• Unable to generate a URL for the named route

AI-assisted analysis of symfony/routing@83fa223250 (2026-09-14). Data as JSON: /api/errors/bb662d7bc77ef3fd. Report an issue: GitHub.

Appendix: source

Thrown at DependencyInjection/Router.php:196

            $resolved = ($this->paramFetcher)($match[1]);

            if (\is_string($resolved) && preg_match('/env_[a-f0-9]{16}_\w+_[a-f0-9]{32}/Ui', $resolved)) {
                throw new RuntimeException(\sprintf('The container parameter "%s" resolves to an env var, which is not allowed in routing configuration.', $match[1]));
            }

            if (\is_scalar($resolved)) {
                $this->collectedParameters[$match[1]] = $resolved;

                if (\is_string($resolved)) {
                    $resolved = $this->resolve($resolved);
                }

                if (\is_scalar($resolved)) {
                    return false === $resolved ? '0' : (string) $resolved;
                }
            }

            throw new RuntimeException(\sprintf('The container parameter "%s", used in the route configuration value "%s", must be a string or numeric, but it is of type "%s".', $match[1], $value, get_debug_type($resolved)));
        }, $value);

        return str_replace('%%', '%', $escapedValue);
    }

    public static function getSubscribedServices(): array
    {
        return [
            'routing.loader' => LoaderInterface::class,
        ];
    }
}

View on GitHub (pinned to 83fa223250)