Can I trace every element the ending rests on to an earlier planting, with chapter and page?
Does anything new and load-bearing arrive for the first time in the ending? New material is allowed; new load is not.
When I reread five earlier scenes with the ending in mind, do they read as intended? Where they do not, have I decided whether the scene or the ending is wrong?
Does the ending answer a pressure the middle built, and not only a question it asked?
Climax and aftermath
Can I point to where the climax ends and the aftermath begins, and say what the aftermath does that the climax could not?
Does the aftermath end within a page of the last decision anyone takes?
Is each thread’s resolution proportional to the space it took?
Domains
Which domains does the ending deliver, which does it gesture at, and which does it refuse, and does each delivered domain have a passage a reader could point to?
Does at least one carrier serve more than one domain, and is there some material that means nothing?
If the book declared a frame, a pattern or an apparatus, does the ending close or modify it?
Questions and ambiguity
Is every question the book raised answered or visibly declined, and none merely dropped?
Can I state any deliberate ambiguity in one sentence, and say what resolving it would cost?
Has the book ended rather than stopped, and can I name the device that tells the reader so?
The last page
Do the last page and three passages from the middle belong to the same book?
Does anyone, character or narrator, explain what the book meant?
Does the final paragraph do work the paragraph before it does not, and do I know why the last word is the one it is?
Exercises
The plant audit. List every element your ending uses as load-bearing, aiming for eight to twenty. Record the chapter and page of each one’s first appearance and of every later one. Mark anything that first appears in the ending, and anything that appears early and then vanishes for more than a third of the book, and for each marked item write the sentence that would plant or maintain it.
Three strategies. Rewrite your ending twice more, as a parallel scene that repeats an earlier situation with its terms altered and as an arrested ending that stops before the outcome, a page each. Do not judge until all three exist, then write one sentence for each saying what that version makes the book about.
The deletion ladder. End the book one paragraph earlier, then one scene, then one chapter, and read each version. Record where the ending is, and what the deleted material was doing for you rather than for the reader.
The closural audit. Beside each sentence of your last three pages write the letters of the domains it serves (plot, character, theme, catharsis, image, form) and mark the sentences that serve none. Read the distribution: letters in blocks mean a serial ending, no inert sentences an over-determined one, and dense letters on the first page and thin ones after mean the ending has already happened.
The counterfactual ending. Write a deliberately unearned ending for your own book, one that resolves by a letter, a stranger or a confession, and run the ten tests on it. Then list which of its failures your real ending shares in a milder form.