Sumthread is a number path puzzle for iPhone: draw one unbroken thread through every tile while your running total hits each target sum, in order. Land exactly on a target and that tile locks with an amber checkpoint ring; the next stretch starts again from zero. The last target has to finish on the last tile.
That is the only rule. It sounds like arithmetic, but it plays like a route puzzle: the numbers tell you how far each stretch can run, and the grid tells you where it can go.
One rule, one thread, no guessing at the end.
How to play a number path puzzle, step by step
Start on the START tile. Its number already counts toward the first target.
Extend the thread up, down, left or right. Drag across tiles or tap one at a time.
Hit the target exactly. The tile rings amber and the sum resets for the next target.
Back up any time by dragging backward or tapping an earlier tile on your path.
Cover every tile. The final target must close on the last free tile.
Two quiet helpers sit on the board: dashed borders show which tiles you can reach next, and amber marks show a neighbor that would complete the target you are working on.
A short tour of the app
Checkpoints. Amber rings mark each target you have landed.Daily Thread. One 4x4 board a day, history kept on your phone.Charcoal Dark. One of five board themes.Collections. From 3x3 starters to 4x5 boards.
Five puzzle collections, from a coffee break to a slow Sunday
Collection
Board size
Feels like
Starter Threads
3x3
Learning the rule
Morning Break
3x4
A five-minute coffee
Deep Weave
4x4
Route and order both matter
Quiet Sunday
4x4
Slower, more thinking
The 4x5 finale
4x5
The longest threads
Finish any board with zero hints and zero undos and it earns the Clean Weave seal. Use hints freely if you like; the seal is just a quiet badge for the purists.
Why we kept it this calm
No ads between boards, and the only clock is a small elapsed-time counter. We wanted a puzzle you could open on a train, close at a stop, and finish on the way home: every step saves automatically, so leaving mid-path costs nothing.
Play is 100% offline with no account and no third-party tracking.
Who should pick something else
If you want a puzzle with hundreds of levels open on day one, or competition against other players, this is a smaller, quieter game than that. The Daily Thread can be shared as an emoji grid, but the listing describes no leaderboards.
Honest limits
Five curated collections, not an endless generator (the daily board is the exception).
iPhone and iPad only; no Android version.
All addition. If you want multiplication or logic grids, look elsewhere.
Questions people ask about Sumthread
What are the rules of Sumthread?
Trace one continuous path through every tile on the grid, moving up, down, left or right, with no diagonals and no revisits. Your running sum must hit the target sums in order. Each time it lands on a target, that tile becomes a checkpoint and the count restarts from zero. The final target must finish on the last tile.
Is Sumthread free?
Sumthread is a free download. At the time of writing the App Store page lists no in-app purchases, and the listing says there are no ads, no account and no third-party tracking.
How long does one puzzle take?
The app is built for a five-minute break. The 3x3 Starter Threads are quick; the 4x4 Deep Weave boards and the largest 4x5 collection take longer.
Is there a daily puzzle?
Yes. The Daily Thread is one fresh 4x4 board each day, with a local completion history and a spoiler-free emoji grid you can share.
Can I stop halfway through a board?
Yes. Every step saves automatically on your iPhone, so you can leave mid-path and pick up at the exact tile later.
Is there a dark mode?
There are five board themes: Warm Ivory, Charcoal Dark, Newsprint Cream, Deep Forest and Clay and Ochre, plus optional step-order badges and high-contrast tile borders.
Is it like Numberlink or Hidato?
It shares the one-path idea, but instead of joining matching numbers or counting up, you add tiles as you go and have to land exactly on each target in sequence.
Thread today's board
Five minutes, one path, no ads.
More about Sumthread
5-minute brain games for a work breakA beginner's guide to 5-minute brain games for a work break: what to look for, a try-it board, and a calm number path puzzle that saves mid-move.
How to solve number path puzzles: 6 tricksStuck on one-line number path puzzles? Six checks (corners, parity, totals, overshoot) worked through on a real 3x3 Sumthread board.
5-minute brain games for a work breakA beginner's guide to 5-minute brain games for a work break: what to look for, a try-it board, and a calm number path puzzle that saves mid-move.
How to solve number path puzzles: 6 tricksStuck on one-line number path puzzles? Six checks (corners, parity, totals, overshoot) worked through on a real 3x3 Sumthread board.
Sumthread
