🔑 KEYSTONE

What is a word bridge?

A word bridge is a chain of four words in which every neighbouring pair joins together to make one longer real word. KEYSTONE gives you the two ends of the chain and asks you to supply the two words in the middle. The chain SOME → DAY → LIGHT → HOUSE works because SOMEDAY, DAYLIGHT and LIGHTHOUSE are all real compound words. Remove the two middle words and you have a puzzle: SOME → ? → ? → HOUSE.

The trick is that the middle words have to do double duty. DAY has to follow SOME and lead into LIGHT. That constraint is what makes a bridge harder than it looks: there are dozens of words that pair with SOME, and dozens that pair with HOUSE, but only a handful that also pair with each other.

How to solve one

1. Work from the more constrained end. Short, common ends like OUT, DOWN or OVER combine with hundreds of words. Unusual ends like WIVES or ABILITY combine with very few. Start where the options are fewest.
2. Use the letter counts. Every KEYSTONE bridge tells you how long each missing word is. Knowing the second word is exactly five letters usually cuts the candidate list by an order of magnitude.
3. Say the joins out loud. Compound words are largely a matter of ear. If FIREPLACE sounds like a word and FIREPLATE does not, your ear is right.
4. Look for hinge words. A small set of English words — OUT, OVER, DOWN, LIGHT, HOUSE, WORK, TIME, HAND, DAY, MAN — sit in the middle of an unusual number of compounds. When you are stuck, try them. We publish the full list: 141 compound word hinges, with every word that joins on each side, and a page of its own for each of the 28 busiest hinges.

Three worked examples

OUT → ? → ? → DATE. Very little precedes DATE: only OUT and UP really work, so the fourth slot wants a word that ends in something DATE can attach to. Working backwards gives MAN (MANDATE), and OUTDOOR plus DOORMAN completes it: OUT → DOOR → MAN → DATE.

HAND → ? → ? → PLACE. PLACE follows FIRE, WORK, COMMON and little else. FIRE is the promising one, and HANDGUN plus GUNFIRE closes the chain: HAND → GUN → FIRE → PLACE.

TEAM → ? → ? → COME. Only OUT and OVER reliably precede COME. OUT is a classic hinge, and TEAMWORK plus WORKOUT gives TEAM → WORK → OUT → COME.

Why compound words behave this way

English builds new nouns by pushing two existing ones together, and it does this far more readily than most European languages. That habit leaves behind a dense, lopsided network: a few hundred very productive words carry most of the connections, and tens of thousands of words sit at the edges with a single link each. Word bridges are a way of walking that network by hand. The reason the same words keep reappearing in KEYSTONE puzzles is not laziness in the puzzle set — it is a real property of the language.

Playing KEYSTONE

There are three bridges every day: a warm-up, a main puzzle and a challenge. They change at midnight in your own time zone. There are no accounts and no cookies; your streak and stats live in your browser only, and weekends never break a streak. Wrong guesses cost nothing, and a hint will fill in one letter if you want it.

You can play today's bridges, work through every day published so far, or read the puzzle of a specific day: Day 1, Day 2, Day 3, Day 4. There is also a daily RSS feed if you would rather be reminded, and an interface for AI agents that plays the whole game over two HTTP requests.