Technologies are provided for validating expression updates. A change to an editable expression can be detected by a client computing device and an expression update describing the detected change can be transmitted to an application server over a bidirectional communication channel. The application server can analyze the expression update to determine whether the detected change resulted in a valid expression. Analyzing the expression update can comprise locating an entity identifier in the detected change and searching a database to determine whether the identified entity exists. The application server can also determine whether a given user has permission to access the identified entity. The application server can transmit expression update validation information back to the client computing device over the bidirectional communication channel. The client computing device can update a user interface displaying the expression based on the validation information.