Déjà Vu is a funny feeling that we're re-living the same moment. A little strange but fairly harmless when it happens to us, but what about our applications? What happens when they get stuck reliving the same requests over and over again? Whether it's caused by users clicking "Submit" twice, or bad network connections, what happens next could make or break your application. Idempotency ensures repeated API calls produce consistent results, saving systems from duplicate charges, mismanaged resources, and confused customers. This talk explains idempotency’s role in building reliable APIs, with practical code examples to show you how to implement it effectively.

We’ll share real-world stories of what happens when idempotency goes wrong (or doesn’t exist), and go through how some of the largest companies in the world choose to implement this technique. Whether you’re a seasoned API developer or new to the concept, you’ll leave with actionable insights and techniques to make your APIs smarter and more user-friendly.