Swimlanes.io is a free webapp for making sequence diagrams. You simply edit the text on the left and the diagram is updated in real time. You can download your sequence diagrams as images or distribute with a link.
Title: Upload API Client -> Server: /upload Server -> Server: Request validation Server --> Client: Error (400) Server -> Validation Service: Validation Service --> Client: Error (400) Validation Service -> Translation Service: Translation Service -> Tms API: Tms API --> Client: Error 400 Translation procedure went wrong Translation Service -> Email Service: Email Service --> Client: Success 200