How difficulty is measured
After building a board, OneTrail has a virtual player try it many times. The player starts from a valid starting dot but, at every fork, picks any remaining line at random. The share of attempts that finish in one go is the board’s difficulty. The lower it is, the more traps the board has.
This matches how hard a puzzle feels, because on an unfamiliar board people also half-guess at each fork.
Difficulty bands
These are the bands in the launch version (1.0).
| Difficulty | Chance of finishing by random play |
|---|---|
| Easy | About 42% or more |
| Normal | About 18–42% |
| Hard | About 6–18% |
| Expert | Under about 6% |
An Expert board finishes less than once in twenty random attempts. This is where you really need the bridges last rule.
Endless combinations
| Goal | Board shape | Size | Difficulty | Return to the start |
|---|---|---|---|---|
| Warm-up | Grid | Small | Easy | On |
| Practise finding the start | Grid or Triangles | Medium | Normal | Off |
| Practise forks | Diagonal | Medium | Hard | On |
| A board to chew on | Mandala or Web | Huge | Expert | Off |
Grid, Diagonal and Triangles use rows and columns of dots; Radial, Mandala and Web use circular layouts, so even at the same size they look and play differently.
60-Second Rush
Solve as many boards as you can in 60 seconds. The first few are small and easy, then they grow as you go. You can Skip a board, so if the start is not obvious, moving on is often better for your score.
In the app
Endless settings
In OneTrail’s Endless, choose the board shape, size (Small, Medium, Large, Huge), difficulty (Easy, Normal, Hard, Expert) and Return to the start, then tap New puzzle. A fresh board is built every time.
60-Second Rush
60-Second Rush shows the seconds left and boards solved at the top, with Undo, Restart and Skip at the bottom.
The Journey difficulty curve
Journey has 8 worlds of 30 stages, 240 boards in all. The board shape changes and difficulty rises world by world, and the last world, Labyrinth, sits in the Expert band.
FAQ
Some boards on the same difficulty feel much easier.
Each difficulty is a band, so “Normal” mixes boards at 18% and at 40%. Knowing the starting dot also changes how hard a board feels.
Where can I see my records?
Your best time is on the Endless settings screen. The bar-chart icon on the home screen opens totals for puzzles solved, lines drawn, time played and your Rush record.
OneTrail: One Line Draw Puzzle
No sign-up, fully offline, and every board is checked to be solvable before you see it. Free on Android.