What does Azure Front Door preserve when redirect fields are left empty?

Definition: In an Azure Front Door Standard or Premium URL redirect action, an empty destination host preserves the incoming host, an empty destination path preserves the incoming path, and an empty query string preserves the incoming query string.

Key facts

• Microsoft describes URL redirect as a rule action that sends clients a redirection response from Front Door in its rule set actions reference.
• Leaving Destination host blank preserves the incoming host.
• Leaving Destination path blank preserves the incoming path. A value that is supplied for this field includes a leading /.
• Leaving Query string blank preserves the incoming query string. A supplied value excludes the leading ?.
• The redirect type is a separate setting. The Azure portal lists Found (302), Moved (301), Temporary Redirect (307) and Permanent Redirect (308).
• In HTTP, a 3xx response uses its Location value as the preferred target resource for automatic redirection, as defined by RFC 9110.

What does each empty field preserve?

Azure Front Door documents three independent preservation rules. An empty Destination host keeps the host from the incoming request. An empty Destination path keeps the incoming path. An empty Query string keeps the incoming query string. Reading these rules together, a redirect action with all three fields empty retains those three URL components while other redirect settings determine the response.

The fields are separate from the redirect protocol. Microsoft lists Match Request, HTTP and HTTPS as the portal values for Redirect protocol, and MatchRequest, Http and Https as the ARM template values. Leaving the host, path and query fields empty therefore does not by itself select HTTP or HTTPS.

How do the fields appear in a rule configuration?

The Azure example uses customHostname, customPath and customQueryString in the UrlRedirect action parameters. A configuration that leaves those destination components empty can be represented as follows, while choosing MatchRequest for the protocol:

{
  "name": "UrlRedirect",
  "parameters": {
    "redirectType": "TemporaryRedirect",
    "destinationProtocol": "MatchRequest",
    "customHostname": "",
    "customPath": "",
    "customQueryString": "",
    "typeName": "DeliveryRuleUrlRedirectActionParameters"
  }
}

When a destination path is supplied instead, the Azure reference requires the leading slash. When a query string is supplied, it omits the leading question mark. Those formatting rules apply to replacement values, while blank fields invoke the documented preservation behavior.

What does the browser or crawler receive?

Front Door sends a redirection response. HTTP represents the target in the Location header, whose value is a single URI reference. RFC 9110 says that, for a 3xx response, this value refers to the preferred target resource for automatically redirecting the request. A relative Location reference is resolved against the target URI.

The selected status code affects the redirect semantics independently of the preserved components. RFC 9110 defines 307 Temporary Redirect as a temporary different URI where an automatic redirect keeps the request method, while 308 Permanent Redirect identifies a new permanent URI. Azure exposes both choices in the portal and the corresponding ARM values in the rule action.

Related terms

• HTTP redirects
• URL parameters
• URL fragment identifiers
• How do I keep campaign parameters through redirects?

FAQ

Does an empty query field remove tracking parameters?

No. Azure documents an empty Query string as preserving the incoming query string. The redirect status and destination protocol remain separate settings.

Does an empty path redirect to the homepage?

No. An empty Destination path preserves the incoming path. If a replacement path is entered, Azure requires it to include the leading /.

Can the redirect change the hostname while keeping the path and query?

Yes. Set a destination host and leave Destination path and Query string empty. Azure documents those two empty fields as preserving the incoming path and incoming query string.

Sources

1. Microsoft Learn, "Rule set actions - Azure Front Door", 2025-06-04
2. RFC Editor, "RFC 9110: HTTP Semantics", June 2022

---

Check how a page reads to answer engines. Open the GEO score analyzer