For Zip and path-puzzle fans who stall mid-board: six tips in the order you need them.
By the Honest Little Apps studio, makers of Sumthread · Updated November 2026
Start where the board gives you no choice: corners and edge tiles with only one or two exits. Then check that what is left can still be covered in one line, and only guess at real forks. Most stalls come from cutting off a corner early, not from bad arithmetic.
The rules are close across the genre. LinkedIn's Zip, reported by Social Media Today in March 2025, asks for one line that hits the numbers in order and fills every cell. Numbrix in Parade magazine bans diagonals, as Zip does. Sumthread, our app, adds a twist: you add up the tiles you pass and must hit each target sum exactly, in order.
Before you touch a tile, read all the targets. In Sumthread the last target must finish on the last remaining tile, so it tells you roughly where you will end.
A corner tile has only two neighbours. If the line passes through it, it must use both. Draw those forced segments early.
Try it: the 4×4 board below has four corners.Shade the board like a chessboard. Every step changes colour, so on a board with an even number of tiles the line starts and ends on different colours. On an odd board (3×3) it starts and ends on the corner colour. That rules out half the possible end tiles in one glance.
Try it: press "Shade the board" below.Say "need 6 more", not "I have 5". A remaining number makes it obvious which neighbour can close the target and which would overshoot. Sumthread shows the same cue on screen, "Need 6 for Target #2".
After each move, look for a tile with one or zero free neighbours left. A tile with one free neighbour must be your end tile; two of them means you have gone wrong.
When stuck, do not wipe the board. Step back to the last place you had a real choice. In Sumthread you drag backward or tap an earlier tile on your path.
Forced moves first, colours second, guesses last.
Targets 11, then 17, then 15. Start on the START tile, move up, down, left or right, and visit every tile once. There is exactly one solution; we checked every possible path.
Dashed tiles are reachable next; amber rings mark tiles where a target locked. In the app, finishing with zero hints and zero undos earns the Clean Weave seal.
Picture a seven-year-old who loves watching a parent do the daily Zip. Zip lives inside the LinkedIn app, so a parent might reach for something offline and ad-free instead. On a 3×3 Sumthread Starter board, the child counts out loud: "3, then 5 makes 8, need 4 more." They hit a wall, tap back two tiles and find the turn.
The checkerboard trick lands well with kids too: colour the corners, and the line has to finish on a corner colour. It is a rule they can see.
What makes it workable for a family: the App Store lists Sumthread at 4+, it plays fully offline with no account, no ads and no third-party tracking, and the first collection is small 3×3 Starter Threads boards. It suits children who can add to 20 or so; younger ones will need a grown-up beside them.
| Sumthread (ours) | LinkedIn Zip | Numbrix | |
|---|---|---|---|
| The line | One path through every tile, no diagonals | One path through every cell | Consecutive numbers, no diagonals |
| The numbers | Hit ordered target sums exactly | Pass numbered dots in order | Fill in the missing numbers |
| Where | iPhone app, offline, no account | Inside LinkedIn | Parade magazine |
| Daily | One Daily Thread (4×4) plus 5 collections | One puzzle a day | Varies by publisher |
Zip from Social Media Today (March 18, 2025); Numbrix from Wikipedia's Hidato article. Sumthread from its App Store listing, read November 4, 2026.
A new 4×4 Daily Thread arrives each day, with spoiler-free emoji sharing when you finish. Get Sumthread free and try the checkerboard check on today's board.