The IIS URL Rewrite Module ships with 3 built-in functions : * ToLower –

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Asked: May 15, 20262026-05-15T08:31:51+00:00 2026-05-15T08:31:51+00:00

The IIS URL Rewrite Module ships with 3 built-in functions : * ToLower –

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The IIS URL Rewrite Module ships with 3 built-in functions:

* ToLower - returns the input string converted to lower case.
* UrlEncode - returns the input string converted to URL-encoded format. This function can be used if the substitution URL in rewrite rule contains special characters (for example non-ASCII or URI-unsafe characters).
* UrlDecode - decodes the URL-encoded input string. This function can be used to decode a condition input before matching it against a pattern.

The functions can be invoked by using the following syntax:
{function_name:any_string}

The question is: can this list be extended by introducing a Replace function that’s available for changing values within a rewrite rule action or condition?

Another way to frame the question: is there any way to do a global replace on a URL coming in using this module?

It seems that you’re limited to using regular expressions and back-references to construct strings – i.e. there’s no search/replace mechanism to replace every instance of X with Y in {REQUEST_URI}, without knowing how many instances there are.

I’ve had a quick glance at the extensibility introduced in the 2.0 RTW and don’t see any ‘light’ means of introducing this.