Stroop Test
The word says one color, the ink is another. Your job is the ink — and that turns out to be surprisingly hard. A free online Stroop test: 24 trials, about a minute, no account, running entirely in your browser. It tells you how many milliseconds the conflicting words cost you.
Take the test
Tap the color the word is printed in. Keys 1–4 work too.
READY
0
ms on conflicting words
That gap is the Stroop effect — the cost of overriding what you read. It narrows as attention control improves, and a value at or below zero on a run this short is usually noise rather than immunity.
Too few clean answers to compare the two conditions. The run needs a couple of correct answers of each kind — worth another go.
- Matching words
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- Conflicting words
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- Correct
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Needs color vision — the task cannot be done without distinguishing the ink. Nothing is uploaded; the result stays in this tab.
What the Stroop test measures
Two things happen when a color word appears in the wrong color. Reading the word is something you have done so many times that it runs by itself; naming a color is not rehearsed to anywhere near that degree.
BLUE
Word and ink agree. Nothing to override, so the answer comes straight out.
fasterBLUE
You have already read “blue”, but the answer is red. That has to be held back first.
slowerSchematic — the distance between those two bars is exactly the number the test above gives you.
The delay is the Stroop effect. Psychologists read it as a window onto selective attention and inhibitory control: keeping a strong but unhelpful response out of the way of a weaker, correct one.
Where it comes from
- 1886
Words beat colors
James McKeen Cattell reports that people read a printed word noticeably faster than they can name a color they are shown. Nobody yet puts the two in conflict.
- 1935
Stroop makes them fight
John Ridley Stroop publishes Studies of interference in serial verbal reactions, from his doctoral work at George Peabody College. His participants read whole cards aloud; the card where words and inks disagreed took far longer than the plain one.
- Since
One of psychology’s most reproduced findings
The effect has held for ninety years across languages, age groups and display technologies that did not exist when Stroop ran it. Versions of the task sit in clinical assessment batteries to this day.
How to read your result
You get one headline number and two supporting ones. They are only worth anything read together.
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The gap
Your mean on conflicting trials minus your mean on matching ones. Subtracting removes how fast you happen to be in general, leaving only what the conflict cost.
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The two means
Shown separately so you can see which side moved. Both high means you were taking your time; only the conflicting one high is the effect in its pure form.
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Correct answers
Out of 24. A small gap earned by tapping fast and wrongly is not the same result as a small gap with everything right — only the second one means anything.
Because the gap is a difference, a quick person and a slow person can score identical interference — which is exactly why it, and not raw speed, is the number worth watching. A positive gap is the normal outcome: it is what the task is designed to produce, and seeing it means the test worked, not that you did badly. A gap near zero on a short run is more often noise than a finding; run it again before you believe it.
What this version cannot tell you
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It is short
24 trials is enough to feel the effect and get a rough number, not enough for a stable measurement. Research versions run several times as many.
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Your equipment is in the number
Touchscreen versus mouse, display latency, whatever else the browser is doing — all of it lands in the milliseconds. Compare your runs to each other on the same device, never to someone else’s.
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Buttons are not speech
The original required saying the color aloud. Choosing among four swatches adds a decision that speaking does not, so values here sit on a different scale from published card norms.
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It is not a diagnosis
The Stroop task appears in clinical batteries, but always alongside other measures and interpreted by someone qualified. A slow run here means you had a slow run here.
Questions about the Stroop test
What is a good Stroop score?
There is no single number, and anyone quoting one for a browser test is guessing. The size of the effect depends on how many trials you run, whether you answer by voice or by pressing a button, your input device, and how tired you are. What is meaningful is your own gap over several runs on the same setup: a smaller gap means the conflicting word cost you less.
Why does the conflicting word slow me down?
For a fluent reader, reading is close to automatic — the word is processed whether or not you want it to be. Naming a color is not automatic to anything like the same degree. When the two disagree, the faster, more practiced process arrives first with the wrong answer and has to be overridden, and that override takes time. The gap you measure is the price of it.
Is this the same as the original 1935 test?
No, and the difference matters. Stroop had people read whole cards aloud and timed the card. This version shows one word at a time and you answer by tapping a color, which adds a step of choosing among four buttons that speaking does not have. It reproduces the effect reliably, but the millisecond values are not comparable to published card-based norms.
Does practising make the effect go away?
The effect shrinks as you get used to the task, and most of that is you getting better at this particular test rather than at attention in general. Whether Stroop-style practice transfers to everyday concentration is genuinely debated among researchers — we would rather say that than sell you a promise.
Do I need an account?
No. Everything runs in your browser, nothing is submitted, and your result is shown to you and then gone when you close the tab.
One run is a snapshot. The trend is the point.
Stroop is one of the games in NEURA, where it is played against a difficulty that adapts to you and feeds a single Focus Index alongside thirteen other games — so what you see is your attention moving over weeks, not one number from one afternoon. That is the part a single page cannot do.