The team switched to Unity to simplify development, adding their own rendering routines, later released as open source, to create a signature look.

The player character is an unnamed boy or young man who explores a surreal and mostly monochromatic environment presented as a 2.5D platform game.

The game is mostly silent, with the exception of occasional musical cues, the boy's vocals, dogs barking, equipment and sound effects.

The player controls the boy who walks, runs, swims, climbs, and uses objects to overcome obstacles and progress in the game.

[4] The boy or young man can die in a multitude of ways, including drowning, being shot with a gun or tranquilizer dart, mauled by dogs, ensnared by security machines, being blown apart by shockwaves, and others.

The boy uses the farm animals and equipment to escape to a seemingly abandoned city where lines of zombie-like people are moved through mind control.

Beyond the city is a large factory of flooded rooms, a shock wave atrium, and a laboratory environment where scientists perform underwater experiments on bodies.

There are some who believe that in the world of Inside, humanity has almost been destroyed because of some ultimate biological catastrophe and that the scientists are making experiments with the Huddle so it can control minds very far away to free itself.

[8] The act of pulling the plug in the final area is similar to the concept of The Matrix, as described by PC Gamer's Tim Clark.

[23] Bramsen's drawing of the Huddle served to guide much of the visual nature and art style for the rest of the game.

[23] To animate it, Grøntved took inspiration from the motion of Nago the demon form of the boar god from Princess Mononoke, the squishiness of the main character of the game Gish, and human behavior during crowd surfing.

[23] Grøntved developed initial animations using what he called the Huddle Potato that simplified the geometries to demonstrate how the being would move and interact with the environment.

[23] Whereas most of the other game animations were based on a combination of pre-set skeletal movements along with the physics engine, the Huddle had to be animated predominantly by a custom physics model developed by Thomas Krog, and implemented by Lasse Jon Fulgsang Pedersen, Søren Trautner Madsen, and Mikkel Bøgeskov Svendsen.

[24] Martin Stig Andersen, with SØS Gunver Ryberg, composed and designed Inside's soundtrack, returning from Limbo.

This enabled additional visual elements tied to the audio; Andersen noted that the boy's chest movements related to breathing are tied to the sound effects he created for his breathing, which themselves are influenced by where the character is in the game, with differences being calm and panicked emotions depending on location.

[25] Andersen collaborated with the design team on the game's general structure and pacing to provide scenes where the music builds up atmospheric tension.

[15] IGN's Ryan McCaffrey wrote that the announcement was a sign of Microsoft's commitment to indie game development[26] and said it was his biggest surprise of the year.

[29] With the delay, Playdead only planned for initial release on Windows and Xbox One,[12] but had expressed interest in other consoles in the future.

[35] 505 Games published Inside and Limbo as a dual-game retail package for Xbox One and PlayStation 4, which was released in September 2017.

[36] Playdead partnered with iam8bit and Abyss Creations (the manufacturers of RealDoll) to create a special release edition of the game for the PlayStation 4 which includes a silicone recreation of the Huddle, along with additional art.