A color word appears in colored ink. Pick the ink color as fast as you can — ignore what the word says.
Choose a round. Keys 1–4 work too.Practice
Answer with the ink color
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Accuracy
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Congruent
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Incongruent
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Stroop effect
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Best average
Your Stroop effect is the incongruent average minus the congruent average (correct answers only). A bigger number means the word slowed you down more.
What the Stroop effect is
In 1935 the psychologist J. Ridley Stroop showed that people name the ink color of a word more slowly when the word spells a different color — BLUE printed in red takes longer than a row of red Xs or the word RED in red. Reading is so practised that it starts on its own, and the meaning of the word competes with the color you are trying to report. That delay is the Stroop effect, and it has become one of the most repeated findings in experimental psychology.
The test is often used as a simple window on interference control — the ability to keep responding to the relevant feature (the ink) while an automatic, irrelevant one (the word) pulls the other way. It is one of the classic tasks grouped under executive functions, alongside working-memory tasks such as the n-back.
How this version measures it
Two kinds of trial. In congruent trials the word and the ink match (GREEN in green). In incongruent trials they differ (GREEN in yellow). Each round is half and half, shuffled.
No easy repeats. The ink color and the word never repeat from one trial to the next, so you cannot gain speed just by pressing the same key again.
Timing. The clock starts when the word appears and stops at your answer, measured with the browser’s high-resolution timer. After 2.5 seconds without an answer the trial counts as a miss.
The score. Only correct answers enter the averages. Your Stroop effect is the incongruent average minus the congruent average.
Reading your result
Almost everyone is slower on incongruent trials, so a positive Stroop effect is normal, not a weakness. With button presses the difference usually lands somewhere between a few tens and a couple of hundred milliseconds; it depends heavily on the device, the number of colors and how much you have practised. Look at accuracy first: answering fast but wrongly shrinks the averages without meaning much.
The effect usually shrinks a little with practice, because you learn to look at the ink rather than read. That is useful to see, but it is practice on this task: research has not shown that getting better at the Stroop test makes people generally better at ignoring distractions in daily life. Treat the number as a snapshot of today, and compare it only with your own results on the same device.
Getting a fair measurement
Do the practice round first. The first few trials are always slow while you learn where the buttons are.
On a computer, rest four fingers on keys 1–4. On a phone, hold it the same way every time; thumbs on a phone are slower than fingers on a keyboard.
Choose 40 trials when you want a steadier number. With 20 trials, one distracted answer moves the average noticeably.
The buttons carry color names and never move, so you never have to match swatches under time pressure. The test itself still depends on seeing the ink: if two of the colors look alike to you, your result will mostly reflect that rather than the Stroop effect.
A color word such as RED or BLUE appears in colored ink. Press the button (or key 1–4) for the ink color and ignore what the word says. Start with the 8-trial practice, then choose 20 or 40 scored trials.
What is a normal Stroop effect?
There is no single norm for an online test, because devices and setups differ. With button presses most people are slower on incongruent trials by a few tens to a couple of hundred milliseconds. Compare your result with your own earlier rounds on the same device rather than with other people.
Why is the Stroop test harder than it looks?
Because reading is automatic for fluent readers. You cannot simply switch it off, so the meaning of the word arrives quickly and competes with the ink color you need to report. Holding back that answer takes a little extra time on every incongruent trial.
Does practising the Stroop test improve concentration?
Your Stroop scores usually improve with practice, but that mostly reflects getting better at this particular task. Studies have not shown that it reliably carries over to concentration in everyday life, so think of it as an interesting measurement and a short mental challenge rather than a treatment.
Is this a medical or clinical Stroop test?
No. It is a free online version for curiosity, classes and self-comparison. Clinical Stroop tests use standard materials, instructions and norms, and are given and interpreted by professionals. If you are worried about attention or memory, talk to a doctor.
Can I use the Stroop test in class?
Yes — it is a classic demonstration in psychology lessons. Students can run the practice round, then a 20-trial round, and compare their congruent and incongruent averages to see the effect in their own data. It works in the browser on school computers and tablets with no sign-up.