Trail Making Test online — free Part A and Part B in your browser

Twenty-five circles scattered across the screen. In Part A you join them in order, 1 through 25. In Part B you alternate between numbers and letters — 1, A, 2, B, 3, C — all the way to 13. Both parts run in a single session and your score is the combined time, so lower is better.

A wrong tap flashes red and adds three seconds, which is roughly how the pen-and-paper version treats a mistake: it is pointed out, you carry on from where you were, and the clock never stopped. Free, no download, no sign-up, and it plays the same with a thumb as with a mouse.

How to play

• Take your first look for free. The clock does not start until you tap the first circle.
• Part A: tap 1, then 2, then 3, up to 25. A line is drawn behind you as you go.
• Part B: alternate. 1, then A, then 2, then B, and so on up to 13. The letters stop at L.
• A wrong tap costs 3 seconds and does not advance the sequence — you still need the circle you missed. The running penalty is in the header, so the total is never a surprise.
• Between the parts the clock pauses, and starts again on your first tap of Part B. Reading the new board is free.
• Your score is total seconds across both parts, plus 3 per wrong tap. Your top 5 is kept on this device.

Why Part B takes twice as long — and what the gap actually measures

The Trail Making Test is one of the oldest paper-and-pencil attention tasks still in regular use. It reached its modern form in the US Army Individual Test Battery in the 1940s and was popularised in neuropsychology by Ralph Reitan in the 1950s. Its appeal has always been that it needs nothing but a sheet, a pen and a stopwatch.

Part A is a visual search: you know the target, you sweep for it, you move on. Part B adds one thing and one thing only — you must hold two sequences at once and swap between them on every step. That single addition is usually enough to roughly double the time, which is why the gap between the two parts is the figure people actually look at. Both parts are dragged around by eyesight, by handwriting speed on paper and, here, by whether you are using a thumb or a mouse; taking the difference cancels most of that out and leaves the bit that is about switching.

The reason B is so much more expensive is that alternating is not free. Every step costs a switch: you have to suppress the sequence you were just running, load the other one, find the target, and then swap back. Psychologists call the extra time a switch cost, and it shows up in almost every task built this way. It is why "4, D" is much harder to hold than "4, 5" even though both are two symbols — you are not remembering more, you are changing rules more often.

The practical trick, and the one worth trying here, is to stop alternating in your head. Instead of thinking "number, now letter, now number", read the next two as a single unit — "4D", then "5E" — and hunt for both at once. That turns two searches with a switch between them into one search for a pair, and it is the single biggest improvement most people find. The second trick is to plan while your finger travels: the circle you want next is usually already in view while you are still moving toward the current one.

Worth saying plainly: this is a browser game, not a clinical assessment. A real Trail Making Test is administered on paper by a trained examiner who watches how you correct errors, and the norms it is scored against depend on your age and education. Nothing here diagnoses anything. Use it the way you would use a stopwatch — to race yourself, and to notice the day you finally get Part B under a minute.

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