In general, the subject matter described in this specification can be embodied in methods, systems, and program products. A computing system receives text that represents content input by a user. A computing system determines a randomness level for a portion of the text. A computing system determines whether the randomness level for the portion of text exceeds a threshold level. A computing system, responsive to determining that the randomness level does not exceed the threshold level, provides the portion of text for processing by a text processing system.