Methods, systems, and computer-storage media having computer-usable instructions embodied thereon, for displaying and inputting symbols are provided. Bopomofo symbols are phonetic representations of Chinese characters. To accommodate all the Bopomofo symbols on a mobile device keyboard without sacrificing key size, the Bopomofo keys are dynamically disabled based on grammar rules and user inputs. For example, a symbol that is not eligible to follow an input symbol is disabled such that it does not distract a user searching for a symbol in the keyboard. Further, specific keys on a keyboard are dynamically replaced with tone keys once a user inputs a symbol. A user interface for displaying the symbols is, thus, consistent and easy to navigate for a user.