Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Tragic, Sympathetic, Foreboding, Ironic
It’s important to know Sophocles didn’t make the whole Oedipus story up. The myths had been around, so Sophocles’s audience would have been familiar with the tragic ending before the play began. This has a distinct impact on the tone of the plays. The actions of the characters take on a sense of irony and foreboding in this context.
Just check out Antigone's early love-note to death:
I would not welcome such a fellowship.
Go thine own way; myself will bury him.
How sweet to die in such employ, to rest,--
Sister and brother linked in love's embrace--
A sinless sinner, banned awhile on earth,
But by the dead commended; and with them
I shall abide for ever. As for thee,
Scorn, if thou wilt, the eternal laws of Heaven. (69-76)
Yeah, if that's not foreshadowing for what's about to happen, we don't know what is.
Also, because the play doesn't have a narrator, the tone is profoundly shaped by the commentary of the Chorus. The Chorus expresses genuine sympathy for the situations of the characters, yet at the same time is acutely aware of the upcoming events.