Friday, August 7, 2026 — three word bridges.
SOME → DAY → LIGHT → HOUSE works because someday, daylight and lighthouse are all words. You are given the two ends; you supply the middle. More than one bridge is often legal, and any legal bridge counts.Warm-up · written by Claude Opus 4.5
5 letters, then 4 letters.
CHECK · MARK
crosscheck · checkmark · markdown — at least 4 different legal bridges exist for this one, so a different answer may well have counted too.
Main · written by GPT-5.2
4 letters, then 4 letters.
BASE · LINE
database · baseline · lineman — other legal bridges may also count.
Challenge · written by GPT-5.5
4 letters, then 4 letters.
MARK · DOWN
benchmark · markdown · downstream — other legal bridges may also count.
Day 15 ran on Friday, August 7, 2026. Its three bridges were CROSS to DOWN, DATA to MAN and BENCH to STREAM. Between them they build nine compound words, all listed at the bottom of this page. Below is the answer to each bridge and what makes it fit.
The answer is CHECK then MARK, which gives crosscheck, checkmark and markdown. The first gap is 5 letters, the second is 4.
This bridge is not unique. KEYSTONE accepts 4 different pairs here and every one of them scores: FIRE · BREAK, OVER · RUN and OVER · TAKE work just as well as the pair above. Ends like these sit in the crowded part of the compound-word network, which is why several routes cross them.
The answer is BASE then LINE, which gives database, baseline and lineman. The first gap is 4 letters, the second is 4.
Only one pair in the KEYSTONE word bank joins DATA to MAN, so this bridge had a single accepted answer. The narrow end is usually the one to solve first.
The answer is MARK then DOWN, which gives benchmark, markdown and downstream. The first gap is 4 letters, the second is 4.
Only one pair in the KEYSTONE word bank joins BENCH to STREAM, so this bridge had a single accepted answer. The narrow end is usually the one to solve first.
CHECK, LINE and DOWN have a page listing every compound built on them and the other chains you can run through them.
Every one of those nine compounds turns on a hinge word doing double duty. If you want to see the whole set KEYSTONE draws from, the reference list of 141 compound word hinges gives the words that attach in front of and behind each one.