Count Back

Three digits go up. You read them, press a key, and they vanish. Now type them in reverse: the last one you saw first, the first one you saw last. Get it right and the next run is four digits, then five, then six, all the way to nine. Get it wrong and you spend one of three lives and try that length again with a fresh run.

Saying a run of digits forwards is storage. Saying it backwards is storage plus manipulation — you have to keep the whole run intact while walking it in the opposite direction — and that second job is what a phone number read out too fast, a mental subtraction, or a spoken set of directions actually costs you. It is also why your backward number lands about two digits below your forward one. That gap is the point of the game, and the board prints both numbers at the end so you can see it rather than take it on trust.

No run you are dealt reads the same in both directions, and none of them is secretly shorter than it looks. The board checks both things before it shows you anything: a run like 5 2 5 would be the same forwards and backwards, so reversing it would cost nothing, and a run like 4 5 6 7 1 is five digits but only two things to hold. Rounds like those quietly inflate the number the task reports, so this board refuses to deal them.

It runs entirely on your device: 0 network requests, works offline. No ads, no account, nothing to buy, and no betting, money or prizes of any kind.

1. Focus the board — click it, or press Tab until it is focused.
2. Read the run while it is up. There is no timer on it. The board shows each digit separately with the position it sits in, so "4 0 7" never reads as "four hundred and seven".
3. Press Enter or Space to hide it when you have it. The digits disappear and the keypad opens.
4. Type the run backwards. The board tells you which position of the original each key answers: your first key is the last digit you saw, your second key the one before it, and so on down to position 1.
5. Move the keypad cursor with the arrow keys — the W, A, S and D keys mirror them — and press Enter or Space to enter the digit under the cursor. You can click a key with the pointer instead; one click enters one digit.
6. Press Backspace, Z or Esc to take the last digit back. A take-back is allowed, but it costs one key from the budget in the status row exactly as entering a digit does — so the keypad is not somewhere to try digits until one feels right.
7. The round closes on its own the moment you have entered as many digits as were shown. There is no submit button to hunt for. The board then shows the run, the run reversed, and what you typed, with the first place the two parted marked.
8. Press any key to move on. A correct round adds a digit to the next one. A wrong round costs a life and repeats the same length with a run you have not seen.
9. The game ends when you have cleared all seven lengths, when three rounds have gone wrong, or when the key budget is spent. It then reports your best backward span and the forward span it implies.

What is a backward digit span, and how do you test yours?

Your backward digit span is the longest run of digits you can hear or read once and then reproduce in reverse order. Testing it is a ladder, and this game is that ladder: start at three digits, add one digit every time you get a run right, and stop when you can no longer do it. The number you report is the longest length you actually completed, not the one you failed on. Two details decide whether the number means anything. First, the run must not read the same in both directions — a palindrome makes the reversal free, so a round like 5 2 5 measures nothing. Second, the run must not be built out of ladders of its own: 4 5 6 7 1 looks like five digits but you can hold it as "four-to-seven, then one", which is two things, so it belongs at a shorter length. This board tests every run against both rules before it deals it, which is why the number it gives you is comparable between rounds and between sessions.

Why is my backward span shorter than my forward span?

Because reversing is extra work done on top of remembering. Holding a run in order is one job; reading it out of your head in the opposite order while it is still there is a second job that uses the same limited space. Most people land about two digits lower backwards than forwards — a forward span of seven usually means a backward span near five. Nothing is wrong if yours drops by three, and nothing is wrong if it only drops by one; the size of the drop is largely how comfortable you are manipulating something you are also holding.

How do I make the number go up?

Chunk, and rehearse the chunks rather than the digits. Almost nobody holds seven separate digits; what they actually hold is three or four groups — "94", "27", "610" — and a group is one item however many digits are in it. Once the run is grouped, reversing it becomes reversing three things instead of seven, and reversing the digits inside each group is a much smaller job. The second habit that helps is deciding on your grouping while the run is still on screen, because regrouping after it has gone means holding the original and the new version at the same time. That is also why this game leaves the run up until you press a key: the time you spend before hiding it is the time you spend organising, and it is not wasted.

Is there any money, betting or in-app purchase in this?

None, and there never will be. There is no currency of any kind here, nothing to buy, no prizes, and no way to risk anything on the outcome. The score is a count of digits you held and lives you did not spend, and it stays in your own browser. There are no ads, no accounts and no trackers on this page.

Does it work offline, and can I play it with a keyboard or a screen reader?

Yes to all three. Once the page has loaded once, everything runs on your device — the generator that draws the runs, the checks that refuse an unfair one, and the comparison that marks your answer. No server takes any part in play, so the game behaves identically with the network off. The whole thing is playable with the arrow keys and Enter alone, and every key on the pad announces the digit printed on it. Nothing is carried by colour: each digit slot also carries a symbol and a word, the review marks right and wrong entries with a tick and a cross as well as a tint, and the live region announces the run digit by digit while it is up, then goes quiet about it the moment it is hidden.

Is this a medical or diagnostic test?

No. It uses the same shape as a long-standing memory procedure, but it is a game: it has lives, a key budget and a score, none of which belong in an assessment, and it is not administered, timed or normed the way a real one would be. Treat the number as something to compare against your own earlier attempts, not as a result about you. If memory is worrying you in daily life, that is a conversation for a clinician, and no browser page is a substitute for one.

Runs are three to nine digits, digits 0 to 9, repeats allowed. Nine is the ceiling for two reasons: almost nobody exceeds it backwards, and it is the longest length for which the board can prove its known-good fallback run is fair. Three lives, and a wrong round costs one and repeats the same length rather than ending the game — but a round is judged only on an exact match, so one transposed pair is a wrong round. The reveal is untimed on purpose, because a timer would measure reading speed as much as memory and would make the game unplayable through a screen reader; there is no scoring pressure to hide the run quickly. The key budget is generous rather than tight — it covers a perfect run, three full-length wrong rounds and three take-backs a round — so you will almost never meet it, but it exists so the game always reaches an ending. There is no hint, no pause, and no way to see a run again once it is hidden. Results are kept in this browser only, so they do not follow you to another device.

Number Span is the forward half of the same measurement — same digits, same ladder, no reversal — and running the two back to back is the cleanest way to see your own gap. Recall Grid asks the same question about places rather than digits, which is a separate span with its own ceiling. Sequence Echo and Tap Order are about order under pressure rather than length. Echo Tiles and Path Recall are the other games here that show something, hide it, and ask for it back, so they reward the same grouping habit.

Bookmark this page (Ctrl+D, or ⌘D on Mac) or install the app — it works offline the next time you need it.