pymetrics Stop Game Explained: Red and Green Circles

In the pymetrics Stop game, circles appear one at a time in the middle of the screen. You press the spacebar when a red circle appears and do nothing when a green one appears. Red comes far more often, so pressing turns into a habit, and the game looks at whether you can hold back in time when green shows up.

pymetrics is owned by Harver, which completed the acquisition in August 2022 and now sells the games as its gamified assessments. This guide explains what you see, the research task behind the game, what it is thought to measure and how to approach it.

The short answer

Red circle: press the spacebar as fast as you can.
Green circle: do nothing and let it pass.
Red is far more common, so the challenge is stopping a press that has become automatic.
There is no feedback during the game, and pymetrics publishes no pass mark.

What you see and do

Official (pymetrics' patent): a red circle asks you to press the spacebar, and a green circle asks you to press nothing.
Prep sites report: one circle at a time in the centre of the screen, each shown for about 1 second. Counts vary from about 70 to 80 circles in roughly 2 minutes. Red is the frequent colour, so runs of red circles build a habit of pressing. Nothing tells you during the game whether you were right.
Not known: the exact number of circles, the share of green ones, the gap between circles and whether every version uses the same colours. pymetrics has not published them.

Red meaning "press" can feel backwards, because red usually means stop. Follow the instructions on screen, whichever way round they are.

Most prep sites describe a go/no-go game, not a stop-signal game where a stop cue follows the go cue after a changing delay. One site describes the stop-signal version, out of line with the patent and the others.

The research task behind it

Stop follows the go/no-go task, a standard test of response inhibition. A meta-analysis by Simmonds, Pekar and Mostofsky (2008) describes the classic design:

Two stimuli: one means respond (go) and one means hold back (no-go).
Go is more frequent. Weighting the task towards go stimuli builds a strong tendency to respond.
Holding back takes effort. Because responding has become the default, each no-go trial calls for active inhibition, and successfully withheld responses are the measure of it.

Researchers usually record three things:

False presses (commission errors): pressing on a no-go stimulus.
Misses (omission errors): not pressing on a go stimulus.
Reaction time on go stimuli.

What it is thought to measure

Harver lists attention and focus among the nine trait areas its games cover, alongside areas such as decision making and risk tolerance, but does not say which game feeds which. In research terms, the Stop game looks at:

Impulse control: holding back on green when pressing has become a habit.
Sustained attention: not missing red circles as the game goes on.
Speed: how quickly you press on red.

pymetrics compares your game measures with those of people who do well in the job. It does not publish how it scores Stop or how it weighs speed against accuracy.

Is there a right answer?

For each circle, yes: pressing on red and holding back on green are the responses the instructions ask for, so misses and false presses can be counted. In that sense Stop is one of the pymetrics games with measurable accuracy, like Digits and Arrows. But pymetrics says its games have no right or wrong answers overall, and it publishes no target for accuracy or reaction time. A sensible aim is quick presses on red with few presses on green.

How long it takes

Prep sites report about 2 minutes. pymetrics says each game takes 1 to 3 minutes and cannot be paused once started, so two minutes of steady attention is the whole game.

A worked example

These numbers are for illustration only. Suppose the game shows 80 circles: 64 red and 16 green.

You miss 2 red circles.
You press on 3 green circles.
Your median reaction time on red is 410 milliseconds.

You responded as asked on 75 of 80 circles, about 94%. Looking at the run in quarters, two of the three false presses came in the first quarter, before you settled into the rhythm, and both misses came in the last quarter, when your attention started to drift. One plausible reading: the early slips came from rushing and the late ones from tiredness. None of it is a verdict; it is simply what the game records.

Tips

Rest a finger lightly on the spacebar so a press costs no movement.
Keep your eyes on the centre of the screen, where every circle appears.
Let the colour register before you press. A fast press only helps if it is on red.
If you press on green, let it go and focus on the next circle. There is no feedback to dwell on.
Play somewhere quiet. The game is short, but it needs your full attention throughout.

Common mistakes

Pressing as soon as anything appears, before the colour has registered.
Slowing right down out of fear of green circles, which turns red circles into misses.
Looking away or down at the keyboard during the run.
Holding the spacebar down instead of pressing it.
Playing on a phone when a computer is available; prep sites advise a keyboard.

Practising the format

Candidate Falcon's Stop practice is an independent version built from the patent and prep-site descriptions. It uses the patent's colours: press for red, hold back on green. A run has 80 circles, each on screen for 1 second with a half-second gap, after a short get-ready pause. One circle in five is green, the first few circles are always red, and two greens never come back to back. You press the spacebar or tap a large Press button; each circle counts once, and there is no feedback until the end.

The review shows your accuracy, misses on red, false presses on green and median reaction time, overall and in four blocks of 20 circles, so you can see whether slips crept in early or late. It is not a pymetrics score or trait report.

It is not pymetrics' game, and it uses original wording and art. Playing needs a plan that includes Harver, which comes with the pymetrics-style games; see pricing. The Arrows game also tests attention, and the free pymetrics guide covers all 12 games.

FAQs

What is the pymetrics stop game?

It is a go/no-go task: press the spacebar for a red circle and do nothing for a green one. Red comes far more often, so the game looks at how well you hold back a response that has become a habit.

Do you press for red or green in the pymetrics stop game?

The patent and prep sites describe pressing for red and holding back on green. Always follow the instructions on your screen.

How many circles are in the Stop game?

pymetrics does not publish a count. Prep sites report about 70 to 80 circles in roughly 2 minutes.

Does the Stop game tell you when you are wrong?

Prep sites say there is no feedback during the game. pymetrics' 2018 FAQ says candidates get a report at the end, although one prep site says some employers share only the outcome.

Is it better to be fast or accurate?

pymetrics does not publish how it weighs the two. Aim to press quickly on red while keeping presses on green rare.

Sources

pymetrics patent WO2015200880A1: the red and green circle task.
Wilson et al. (2021), Building and Auditing Fair Algorithms, with pymetrics co-authors: how game measures are compared with high performers.
Harver: gamified assessments (read October 2026): trait areas and the games after the acquisition.
pymetrics candidate FAQ, employer-hosted copy (2018): no right or wrong answer and timing.
Simmonds, D. J., Pekar, J. J. and Mostofsky, S. H. (2008). Meta-analysis of Go/No-go tasks demonstrating that fMRI activation associated with response inhibition is task-dependent. Neuropsychologia, 46(1), 224–232.
Prep sites (descriptions, not official): MBB Prep and JobTestPrep.

Candidate Falcon is independent and not affiliated with pymetrics, Harver or any employer.