But coroner Clare Bailey told last Friday's inquest the police investigation "painted a picture of both being happy and content".
"No one was aware of them having any issues,"she added.
Police analysed Snapchat messages which showed the boys standing at the top of the cliffs while taking "a selfie-style video". Concluding that both deaths were accidents, the coroner added: "They are stood extremely close to the cliff edge, in very good spirits.
"This evidence supports the theory they had fallen as a result of a terrible accident."
Teesside Coroner's Court was told both teenagers were "happy and popular young men".
Alex's mother, Jane Hume, told the hearing her son was a happy boy who "always had a cheeky little smile".
Brotton's Freeburgh Academy, where the teenagers went to school, said: "Harry and Alex were lovely young men who had so much to live for. They were both very positive members of our school team and we have very fond memories of them."