Git (Version Control).

Without version control you end up with folders named 'website_final_v3_new'. Git replaces that with a complete history: every finished change is saved as a commit, with a short description of what was changed and why. All the commits together form the repository, the complete archive of the project. If something goes wrong, you can jump back to any earlier state.

Branches let you work on a new feature without putting the running version at risk. The main line (often called main) corresponds to the live website; new work happens on separate branches and is merged only after review. Platforms such as GitHub, GitLab or Bitbucket store repositories online, enable code reviews and automatically trigger tests or a deployment with every change. Git itself is the tool; GitHub is one of several places where it is used.

For clients, Git is above all a question of ownership and independence. Whoever owns the repository of their website or app can engage a different agency at any time without starting from scratch. If the code sits only on one developer's computer or in an agency's account, the result is vendor lock-in, which becomes expensive when you want to switch.

Git is also the foundation of modern workflows. A change is implemented on a branch, built automatically and deployed to a staging environment for review. After approval it is merged into the main line and goes live. Every step is documented, and a faulty update can be rolled back with a single command.