Stroop Test online
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 — the classic color-word task: 20 trials, about a minute, no account, running entirely in your browser. It tells you how many milliseconds the conflicting words cost you, and says in plain words how large that cost is.
Take the test
Tap the color the word is printed in. Keys 1–4 work too.
Tap the digit with the higher value, whatever size it is. Keys 1–2 work too.
READY
0
ms of interference
The conflicting trials barely slowed you down. On a run this short that can be luck as easily as control — run it again before you believe it.
This is the ordinary result: the gap is what the task is built to produce, so seeing it means the test worked, not that you did badly.
The conflicting trials cost you real time. That is common when you are tired, rushed, or meeting the task for the first time.
The automatic answer ran ahead of you on most conflicting trials. Answering a little more deliberately usually shrinks this more than trying to go faster.
Every conflicting trial had to be fought down. One distracted patch moves this a long way, so it is worth another run before reading much into it.
Too few clean answers to compare the two conditions. The run needs a couple of correct answers of each kind — worth another go.
ms = milliseconds, from the stimulus appearing to your tap. This is the interference cost: your average on conflicting trials minus matching ones.
- Matching
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- Conflicting
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- Correct
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Needs color vision — the task cannot be done without distinguishing the ink. When a run ends it is sent to us — its times, which conflict, whether each answer was right, the input device, the language of this page — so the chart of everyone’s runs can exist; nothing that identifies you goes with it.
No color vision needed and no words on screen — the digits are the whole task. When a run ends it is sent to us — its times, which conflict, whether each answer was right, the input device, the language of this page — so the chart of everyone’s runs can exist; nothing that identifies you goes with it.
That was a single run. In the app it becomes a short daily session, with a Focus Index to show for it.
Point your camera at the code — the App Store opens.
What the Stroop color-word 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.
Two conflicts: color or numerical
The switch above the test changes what fights what. The measurement does not change at all: the same 20 trials, the same two conditions, the same gap in milliseconds.
Color is Stroop's own task — the word says one color, the ink is another, and reading gets in the way of naming. Numerical swaps the words for two digits printed at different physical sizes, and asks which digit is worth more. On matching trials the higher value is also the physically bigger one; on conflicting trials the bigger digit is the smaller number, and the size has to be held back the way the word does in the color version. It is the size–value variant psychologists call the numerical Stroop.
Two things make it worth having. It needs no color vision, so it is playable by anyone for whom the color version is not a fair test in the first place. And it puts no words on screen — the entire task is two digits and two arrows — so it is the one version of this test that looks identical in every language we ship. Switching conflicts clears the board: a run half-played under one conflict is not a result under the other.
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 20. 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.
Under the number the test also names the size of the effect — from minimal to very strong, on five steps. That is a description of this run and nothing else: it says how big your own gap was, never how you compare to anybody. The comparison we do publish is the shape of everyone’s runs, not a place in a queue — see the callout below for why that distinction is the honest one here.
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
20 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.
What is the numerical Stroop task?
It is the same interference, with size standing in for ink. Two digits appear at different physical sizes and you tap the one with the higher value; on conflicting trials the physically bigger digit is the smaller number, so its size has to be overridden the way a word does in the color version. The switch above the test runs it: same 20 trials, same two condition means, same gap. It needs no color vision, and it puts no words on screen at all — just two digits and two arrows — so what you see is identical in any language.
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 practicing 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.
How do you do the Stroop test?
A color word appears, printed in an ink that usually disagrees with it, and you answer with the ink — not the word. Tap one of the four color buttons, or press keys 1 to 4 if you are on a keyboard. There is nothing to set up and no practice block: the run is 20 trials long, takes about a minute, and the result appears the moment the last one is answered.
Is the Stroop test used to screen for ADHD?
No, and a version in a browser tab least of all. Stroop tasks do appear in clinical and research batteries where attention is being assessed, but always next to other measures, administered under controlled conditions and interpreted by someone qualified — and a large gap on its own does not identify any condition. If you are worried about your attention, this page is not the place to find an answer; a clinician is.
What are the emotional and numerical Stroop variants?
Both keep the idea and change what is in conflict. The emotional Stroop replaces color words with emotionally loaded ones and asks for the ink anyway, on the theory that a word you care about is harder to ignore. The numerical Stroop puts quantity against size — a small 8 beside a large 3 — and asks which is numerically larger. This page runs the classic color-word version and the numerical one, under the mode switch above. The emotional variant is the one we do not ship: loading words with distress to measure attention is not something a page you opened on your own should do to you.
Do I need an account?
No, and there is nothing to sign up for. The test itself runs in your browser; when a run ends, the run is sent so that the chart of everyone’s runs can exist. What goes with it is the run and only the run — its times, which conflict, whether each answer was right, the input device and the language of this page. Nothing that identifies you goes with it, and nothing about you outlives the tab.
One run is a snapshot. The trend is the point.
Stroop is one of NEURA's 19 games, played there against a difficulty that adapts to you, with every run feeding a single Focus Index — 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.
