Systems and methods relate to creating applications using building blocks linked together with metadata. A user interface can enable a user to create an application. Creating the application can include defining a new building block configured to generate output data. The new building block can include one or more existing building blocks and the metadata associated with the existing building blocks. For example, a building block can include at least one input/output (I/O) feature configured to receive inputs and/or generate outputs. Further, the existing building block can correspond to a data structure including external I/O features. The new building block can be linked to an existing building block by mapping an external I/O feature of the existing building block to an open I/O feature of the new building block. The mapping can be stored in metadata associated with the new building block.