When Tcl is embedded in a design tool, the designer using the tool can write Tcl scripts that automate repetitive functions and extend the basic functions of the application. For example, a circuit designer using a Tcl-enabled simulation tool can write a Tcl script that runs a series of simulations on a design, records data at key points, and presents the results to the user. This script can be saved for use as a regression test at later stages of the design. Using Tcl as an embedded command language turns a simple tool with a few basic features into a powerful programmable application.
Most designers end up using multiple tools from different vendors.
Having a single common command language means that a designer only needs to learn Tcl in order to automate multiple tools. Furthermore, Tcl can also be used to coordinate and integrate different applications, which benefits both customers and vendors. In the early days, each company developed its own proprietary scripting approach. Because of its large open source community, Tcl evolved and acquired new features much faster than the proprietary scripting languages, and the companies using Tcl benefited from these improvements. Eventually, many of the smaller companies were acquired by larger companies, which introduced Tcl into the parent organizations.