IndexOf()

Returns the position at which a substring occurs within a string. The function uses 1-based indexing—that is, the first character in the string is counted as position 1. A result of 0 indicates that the substring wasn’t found in the source string.

This function became available in Marketing Cloud Next during the Summer ’26 release (API version 67.0).

1IndexOf(sourceString, substring)

The IndexOf() function has two parameters:

• sourceString (string): Required. The string to analyze.
• substring (string): Required. The character or substring to find the position of.

To use the function, pass it a source string, and the substring that you want to find in that string.

This example finds a single character within a string and returns its position. It uses simple conditional logic to determine which text to output.

1%%[
2  Var @tickedId, @isTicketClassC
3  Set @ticketId = "29487C-22934"
4  Set @isTicketClassC = IndexOf(@ticketId, "C")
5  If @isTicketClassC == 6 then
6]%%
7<p>Your ticket is Class C</p>
8%%[ Else ]%%
9<p>Your ticket is not Class C</p>
10%%[ EndIf ]%%

The example outputs the result of the function.

1Your ticket is Class C

This example finds a substring that consists of multiple consecutive characters.

1%%[
2  Var @lipsum, @position, @substringToFind
3  Set @lipsum = "Lorem ipsum dolor sit amet."
4  Set @substringToFind = "dolor"
5  Set @position = IndexOf(@lipsum, @substringToFind)
6]%%
7<p>Found the string "%%=v(@substringToFind)=%%" at position %%=v(@position)=%%.</p>

The function returns the position at which the substring begins.

1Found the string "dolor" at position 13.