How and where to describe technical specifications for a front-end developer?

Question

Project management

I am working on one project, writing backend. I also have to look for and distribute tasks to front-end developers. Now this is a mobile application, and SPA as an admin panel for the customer.
To document the API, I think to start using swagger. But what about setting tasks for front-ends?
Example: there is a mobile application design. Now I am describing api, then in text form I write a task to the programmer:
click on this button - pull this url, insert the fields from the response here and here. Etc.
How is it usually organized and what services can be used for this?

Answer 1

Nobody came up with anything new instead of a wiki. Any images and diagrams must be accompanied by explanatory text and/or sequence diagrams. So the screens are drawn in whatever is convenient, and then we paint their elements in the form of documentation and for each element separately at least pages.
For collaborative work, the notorious Confluence or its analogues are always convenient

Answer 2

You can sketch interface prototypes with UX logic in balsamiq, WireframeSketcher and the like..