Color words appear in colored ink. Your job is to press the color of the ink, not the color the word names. Matching words are easy; conflicting ones slow you down. The test measures exactly how much, in milliseconds.
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Name the ink color, not the word
A color word appears in colored ink. Press the button for the color of the ink as fast as you can. Some words match their ink (BLUE), others conflict (GREEN → answer Red).
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Your Stroop effect
0ms
Keyboard: RBGP or 1–4. Press Esc to stop.
Average reaction time by trial type (correct answers)Every trial (✕ = wrong or timed out)
Your recent tests
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How to use the Stroop Test
Pick the number of trials (48 is a good default) and whether to include neutral XXXX trials, then press Start test.
Look at the + in the middle; a color word will replace it.
Press the ink color with the on-screen buttons or the keys R, B, G, P (or 1 to 4). Ignore what the word says.
Answer fast but accurately: each word disappears after the time limit.
Read your Stroop effect, check the charts, and download the CSV if you need the raw data.
Why the Stroop effect happens
For a fluent reader, recognising a written word is fast and largely automatic, while naming a color takes deliberate attention. When the two disagree, the brain has to suppress the automatic answer (the word) and select the requested one (the ink). That extra step of selective attention and response inhibition costs time and causes most of the errors you see on incongruent trials. Researchers use Stroop-type tasks to study attention, executive control and how these change with age, fatigue or practice.
How to read your results
Measure
Formula
What it tells you
Stroop effect
mean RT incongruent − mean RT congruent
Total cost of conflict between word and ink
Stroop effect %
effect ÷ mean RT congruent × 100
Cost relative to your overall speed, fairer when comparing fast and slow responders
Interference
mean RT incongruent − mean RT neutral
Slowing caused by a conflicting word (needs neutral trials)
Facilitation
mean RT neutral − mean RT congruent
Speed-up when the word agrees with the ink
Error cost
error % incongruent − error % congruent
Whether conflict makes you less accurate, not only slower
Look at speed and accuracy together. If you are very fast but make many errors on incongruent words, you are trading accuracy for speed; slowing down slightly often gives a more honest measure.
Getting reliable numbers
Use a keyboard or tap the buttons with one finger from a fixed position. Moving a mouse between buttons adds travel time.
Run 48 or 96 trials. With only a few trials, one slow answer can change your averages a lot.
Your first test includes learning the button positions. Do a second run before comparing results.
For a classroom demonstration, download the CSV from several people and compare congruent and incongruent means.
Frequently asked questions
What is the Stroop effect?
The Stroop effect is the delay in naming the ink color of a word when the word itself names a different color, for example the word GREEN printed in red ink. It was described by John Ridley Stroop in 1935. Reading is so automatic for fluent readers that the word's meaning competes with the color you are trying to report.
How is my Stroop effect calculated?
Stroop effect = mean reaction time on incongruent trials − mean reaction time on congruent trials. Only correct answers of at least 150 ms count, so slips and anticipations do not distort the averages. The percentage shown is the effect divided by your congruent mean.
What is a normal Stroop effect?
Almost everyone is slower on incongruent trials. The size depends heavily on the version of the test: number of colors, key-press versus spoken answers, practice and the number of trials. In key-press versions like this one a difference of several tens of milliseconds up to roughly 100 to 150 ms is common, and your own result can vary between sessions.
What are congruent, incongruent and neutral trials?
Congruent: the word and the ink match (BLUE in blue). Incongruent: they conflict (BLUE in red). Neutral: a non-word such as XXXX in a color, which measures color naming without any word to read. With neutral trials you can split the effect into interference (incongruent − neutral) and facilitation (neutral − congruent).
Why does the test use purple instead of yellow?
Yellow text is hard to read on a white background, which would slow down yellow trials for reasons that have nothing to do with the Stroop effect. Red, blue, green and purple are all clearly visible on white.
Can I use this Stroop test if I am color blind?
Red and green can be hard to tell apart with red-green color vision deficiency, which would make the test measure color discrimination rather than interference. If that applies to you, treat the results with care or try our color blindness test first.
Is this a medical or diagnostic test?
No. Clinical Stroop tests use standardised materials, instructions and norms. This online version is for learning, classroom demonstrations and self-curiosity, and the results stay in your browser.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.