You can buy impressions.
You can’t buy wins.

How it works

Two projects. One question: which would you click?

Every answer is a vote. Ratings rise and fall with wins and losses, like chess.

Ten ranked votes earns you a listing for your own project. No account, no email.

A project becomes officially ranked after 20 duels; before that its rating is provisional.

Money can buy a queue slot or extra appearances. It cannot buy a rating, ever.

Every vote ever cast is kept, append-only, and the rankings can be recomputed from that log by anyone who doubts them.

The rest of this page is the machinery, in the open, for anyone who wants to check.

Fairness & methodology

Everything below is the exact mechanism — the numbers, the hashes, the logs. None of it is required reading to play.

The rules

1. Two projects, picked by the server. You never choose the matchup. Side A is drawn at random, weighted by exposure credits; side B is drawn from the projects rated within 300 points of it, so the duel is close enough to be a real question.
2. You click one. That is the whole vote. There is nothing to sign up for, no comment box, no score to game.
3. Ratings move by Elo. Winner takes points from loser, more when the result was a surprise. New projects move fast (K=32) until they have twenty rated duels, then settle (K=16). A project needs twenty rated duels before it can be ranked at all.
4. The next duel arrives with the result. One round trip. That is a design rule, not an optimisation — a discovery game you have to wait for is not a game.

The invariant

You can buy impressions. You can’t buy wins.

Money in Duel buys one thing: how often a project is drawn as side A. It never touches a rating, never weights a vote, and never removes another project from the pool. A project with no exposure credits is drawn less often than one that has them, and beats it just as hard when it wins. Three more promises hold the first one up:

• Only server-drawn duels count. Challenge pages — the head-to-heads anyone can create and share — are spectacle. Their votes are recorded and tallied, and they never enter the rating system. You cannot vote your own project up by sending your friends a link.
• The vote log is append-only. Every vote is kept forever with the context that produced it: both ratings before the duel, the expected score, the K in force, and a keyed hash of the voter, address and browser. Nothing is ever updated or deleted. The ratings you see are a cache; the log is the truth, and it can be recomputed or re-weighted from scratch if the scoring ever needs to change.
• Free projects never starve. Weighting is logarithmic, so buying exposure has sharply diminishing returns, and every listed project stays eligible for every draw.

Unlocking a submission

Listing a project costs votes, not money. Every ten ranked votes — the server-drawn duels, never the challenge pages — earns one submission credit; /submit spends it. Paste a URL, we read the page’s own title, description and preview image, you edit the name and the one-liner, and it enters the pool at 1500 — the same rating everything else started from.

The reason the price is votes: someone who has judged ten duels has seen what a good card looks like, and a queue that costs attention is one that cannot be flooded from a script.

Who you are

Nobody, and deliberately. There are no accounts. Your identity is a random id in a signed cookie; your votes and your unspent submission credits hang off it. Clear the cookie and you are a new voter with nothing. We store keyed hashes of your address and browser string with each vote, for rate limiting and for the ability to re-weight the ratings later if a voting ring turns up — never the values themselves.

The production site also loads Google Analytics, for reach reporting. It sets its own cookie — not ours — and sends Google your client id, IP address, user agent and the page you’re on. It is separate from everything above: the rankings and the duel mechanics never read it, and it never reads them.