Green’s Dictionary of Slang

1. a good thing.

1871		‘George Eliot’ Middlemarch I 188: Ay, ay: money’s a good egg; and if you‘ve got money to leave behind you, lay it in a warm nest.
1886		‘’Arry at the Smoking Concert’ in Punch 13 Nov. in P. Marks (2006) 67: This combining of larks and of lotion with ’Armony seems a good egg.
1921		Wodehouse Indiscretions of Archie Ch. iv: Giving it as his considered opinion that the Hotel Cosmopolis on closer inspection appeared to be a good egg, one of the best and brightest, and a bit of all right.

2. an admirable person; thus good-eggishness, the quality of being such a person.

1856		Life in Boston & N.Y. (Boston, MA) 25 Oct. n.p.: N—n K—n says he will give S. Ann H—f one more rip [...] Well, I am glad you are a good egg.
1901		Hull Dly Mail 31 May 2/7: [headline] A Good Egg Story.
1907		Gem 16 Mar. 4: ‘Heap good egg, Dorien,’ said Badger.
1919		Marvel 1 Mar. 6: ‘Excellent egg!’ thought Fane.
1923		O.O. McIntyre New York Day by Day 31 May [synd. col.] There’s a good egg. He’s carrying all his wife’s bundles and smiling.
1934		Wodehouse Right Ho, Jeeves 28: I [...] have never wavered in my cordial appreciation of her humanity, sporting qualities and general good-eggishness.
1939		H. Miller Tropic of Capricorn (1964) 161: Not very bright, to be sure, but a good egg, a companion.
1944		J.T. Farrell To Whom It May Concern 23: He’s a bigshot in pictures and he’s a good egg.
1947		C. Willingham End as a Man (1952) 189: And he’s really a nice egg, too.
1958		(con. 1950) E. Frankel Band of Brothers 3: Seems like a good egg [...] I was gasin’ with him back at the C.P.
1967		E. Shepard Doom Pussy 137: The fellows are good eggs.
1970		D. Ponicsan Last Detail 100: You’re a good old egg.
1989		M. Amis London Fields 445: The author, a Catholic and obviously a good egg.
1998		(con. 1940s) P. Cumper One Bright Child 78: Good egg, old Norman.
2000		M. Amis Experience 340: Eric Shorter, a good egg from the Garrick, pays a visit.
2016		A. Wheatle Crongton Knights 98: She was a good egg, though.
2024		J. Meades Empty Wigs (t/s) 175: [T]he rough diamond rustics, good eggs if less than couth.