The episode follows Cooper (Wyatt Russell), an American who playtests an upcoming augmented reality game in London while travelling.

The episode was inspired by an idea Brooker had for an augmented reality Whac-A-Mole game which increased in speed until the subject went crazy.

After his father dies from Alzheimer's disease, Cooper (Wyatt Russell) travels the world, ignoring phone calls from his mother.

He is forced to stay with her after his bank account is drained when he becomes victim to identity theft, but finds a paid offer to playtest a game for SaitoGemu.

Cooper was in fact killed within 0.04 seconds by a phone call from his mother causing signal interference with the device, the subsequent experience existing only in his head.

[11] Brooker then conceived of adding a haunted house concept, where the augmented reality technology would dynamically change what the person saw in response to their fears.

Brooker compared the last twist to a "punch line" ending of a Twilight Zone episode, initially concerned that it would be too humorous, but finding it "harrowing and horrifying" in the edit.

[11] Alternate scenes were a key concept of the later interactive film Black Mirror: Bandersnatch, which incorporated viewer decisions into the story.

Brooker noted that they were initially going to have the song John-Kamen sang in "Fifteen Million Merits" playing on the radio in one scene but were unable due to a licensing issue.

[5][17] Other roles include Wunmi Mosaku as Katie, who runs the experiment, and Ken Yamamura as Shou, the video game company owner.

Initially, production would have taken place in Tokyo, a key hub for video game development, with mansion scenes filmed in the United Kingdom, but the writers found it difficult to explain in-story why such a house would exist in or near Japan.

Instead, they decided to make the episode take place in London, a location they had ready access to but had not prominently featured in the series before.

[19] The sets for SaitoGemu were created from an abandoned school building, while scenes in Harlech House were filmed in the home of an elderly woman.

[11] The animation company Framestore worked on the effects, tasked with making the small realistic spider that Cooper first sees and the deformed version that later appears.

[12] Trachtenberg wanted the penultimate scene, with Cooper returning home, as a one-shot take, given the drastic change in tone it gave the episode.

[11] The episode is a work of psychological horror;[20] Adam Chitwood of Collider found it "genuinely terrifying", while Chancellor Agard of Entertainment Weekly believed it to contain "one of the show's most viscerally disturbing scenes".

"[24] In relation to the mushroom drawing inspiration from Cooper's fears, Roxanne Sancto of Paste wrote that people have aimed to explore "this confrontation with the darkest corners of our subconscious" before modern technology, such as with dream analysis, hallucinogens or hypnosis.

[25] The character Katie says that the experimental technology adds "layers on top of reality", with Bramesco commenting that the episode's construction is this in reverse.

[23] Bryan Bishop of The Verge found that other themes covered include the ethics of experiments on human beings and the importance of resolving family issues.

Abad-Santos further said that though viewers may expect characters to be revealed as evil, none are, and concluded that "the greatest threat to yourself isn't the strangers you meet through your phone, but rather your own dishonesty".

[27] The episode shows futuristic technology at the headquarters of SaitoGemu, Bishop describing the setting as "full of all-white rooms and silent worker bees tapping away dutifully behind minimalist visor displays".

[29] To hint that most of the episode takes place inside Cooper's mind, features from early scenes were incorporated as background elements later on.

[14] Cooper's method of killing Sonja by slamming her head onto the knife through his shoulder evokes the position in which the pair woke up that morning.

[26] Cooper also sits next to a girl whose face is used for a creepy portrait and sees a SaitoGemu employee designing a costume which later appears on Josh Peters.

The site's summary describes that its "psychologically horrifying world ... is nicely counterbalanced by the sheer likability of the episode's protagonist".

[20][21] Bramesco wrote that he "pulls off a difficult performance",[23] whilst Mullane said that Russell was "so convincingly terrified and frazzled throughout that you'll forget you're watching a piece of fiction".

IndieWire authors ranked the 22 Black Mirror instalments excluding Bandersnatch by quality, giving "Playtest" a position of 10th.

[40] Meanwhile, Brian Tallerico of Vulture rated Russell's performance the sixth best of Black Mirror, praising him as "a truly charismatic and engaging actor".

[49][50][51] The episode was also submitted for consideration alongside "Nosedive" and "San Junipero" for an Art Directors Guild award for Excellence in Production Design for a Television Movie or Limited Series, for which it was nominated.