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.

Availability

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

Syntax

IndexOf(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.

Usage

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

Finding a Single Character

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

%%[
  Var @tickedId, @isTicketClassC
  Set @ticketId = "29487C-22934"
  Set @isTicketClassC = IndexOf(@ticketId, "C")
  If @isTicketClassC == 6 then
]%%
<p>Your ticket is Class C</p>
%%[ Else ]%%
<p>Your ticket is not Class C</p>
%%[ EndIf ]%%

The example outputs the result of the function.

Your ticket is Class C

Finding a Substring with Multiple Characters

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

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

The function returns the position at which the substring begins.

Found the string "dolor" at position 13.