The name
John Wanamaker sold clothes in Philadelphia. He invented the price tag. He bought the first full-page newspaper advertisement anyone had seen. And he is credited with the most repeated sentence in the history of marketing:
“Half the money I spend on advertising is wasted; the trouble is I don't know which half.”
He almost certainly never said it. Researchers have hunted the quote for decades. It is not in anything he wrote, and not in anything he is reliably reported to have said. The line still gets quoted in a thousand agency decks every year. Its source does not survive a single check.
That is this whole project, in one quote. Marketing runs on ideas that are repeated everywhere, useful in the room, and never tested. It rarely separates those from the ideas that have been tested and held up. This index does that sorting in public.
What this is
79 marketing tools, sorted by the question you are stuck on rather than by discipline. Every entry carries two columns that framework lists leave out. One is an evidence tier: how much proof sits under the tool. The other is a failure condition: the moment the tool stops telling you the truth.
The tiers are Law, Frame, Folklore. A tier measures the evidence, not the usefulness. Some of the best known tools here sit in Folklore. That is the finding, not an oversight. A Folklore tool can be the right thing to reach for. It just should not be your answer when someone asks how you know.
You can start from the 9 questions. Or start from whatever is broken right now, which is how most people actually turn up.
What this is not
It is not advice and it is not a ranking. The index will not pick a tool for you. It tells you what each one can and cannot carry, and then the choice is yours. It is not a literature review either. Where the original source exists, we link it. Where we only found a summary, we say so.
No vendor money. Nothing here is sponsored and nothing will be. The day a measurement company pays for a place on this site, every Folklore mark becomes suspect. That door stays shut.
Corrections
Some of this is wrong. Checking has already overturned several widely repeated claims, and those entries were rewritten rather than left standing. If you find an error, send it. If you find the original source for something that currently rests on a summary, send that too. The method page explains what would change a verdict.