octobercms/october · warning · October\Rain\Exception\ValidationException

Route prefix must start with a forward slash (/)

Error message

Route prefix must start with a forward slash (/)

What it means

SiteDefinition::beforeValidate() enforces the route prefix format for prefixed multisite sites: when is_prefixed is on, route_prefix must start with '/' and must not be exactly '/'. Any other value (missing slash, trailing-only slash, bare '/' or empty) throws a ValidationException on the route_prefix field.

Source

Thrown at modules/system/models/SiteDefinition.php:133

            'is_enabled_edit' => true,
            'group_id' => null,
            'group' => null,
        ];
        $site->syncOriginal();
        return $site;
    }

    /**
     * beforeValidate
     */
    public function beforeValidate()
    {
        if ($this->is_custom_url && !Url::isValidUrl($this->app_url)) {
            throw new ValidationException(['app_url' => __("Please specify a valid URL")]);
        }

        if ($this->is_prefixed && (substr($this->route_prefix, 0, 1) !== '/' || $this->route_prefix === '/')) {
            throw new ValidationException(['route_prefix' => __("Route prefix must start with a forward slash (/)")]);
        }

        if ($this->is_host_restricted && !$this->isAllowHostsValid()) {
            throw new ValidationException(['allow_hosts' => __("Please specify a valid hostname")]);
        }

        $this->fallback_locale = $this->getFallbackLocale($this->locale);
    }

    /**
     * getFallbackLocale attempts to extract the fallback language from the locale.
     * @return string
     */
    protected function getFallbackLocale($locale)
    {
        if ($position = strpos($locale, '-')) {
            $target = substr($locale, 0, $position);
            $available = $this->getLocaleOptions();

View on GitHub (pinned to b608633a7e)

Solutions

1. Set the prefix with a leading slash and a non-empty segment: /en, /de
2. Disable the 'prefixed' option if the site should not use a route prefix at all
3. When saving programmatically, normalize before save: '/' . trim($prefix, '/') when non-empty

Example fix

# before
route_prefix: "en"

# after
route_prefix: "/en"

$prefix = trim((string) $site->route_prefix);
if ($prefix !== '' && $prefix !== '/') {
    $site->route_prefix = '/' . trim($prefix, '/');
}

When it happens

Trigger: Saving a site with is_prefixed enabled and route_prefix 'en', 'en/', '/', or an empty string.

Common situations: Typing the locale/prefix without the leading slash in the site form; assuming '/' alone is valid for the root; provisioning sites from config where the prefix lost its slash.

Related errors

• Please specify a valid URL
• cms::lang.page.invalid_url
• Cannot find the requested row group.
• Inspector container ${$containerHolder.data['inspector-conta
• Cannot switch to container: a container element is not found

AI-assisted analysis of octobercms/october@b608633a7e (2026-08-21). Data as JSON: /api/errors/4546f993103b876e. Report an issue: GitHub.