Definition
A time loop is a mechanic in which the state of the world returns to its initial value after a fixed span of time, and only the player's knowledge carries over. The player's verb is "go round again". What changes from lap to lap is not the position of a piece or a door, but how much the player knows about the world.
The win condition has two layers. The needed facts must have been gathered, and they must then be spent in the right order inside a single lap. Progress lives in the player's head rather than in a save file, and doors are opened by knowledge rather than by items. Because the world state is thrown away every lap, an unrecoverable dead end is structurally hard to produce.
Origins and lineage
The earliest well-known digital model is The Legend of Zelda: Majora's Mask, which Nintendo released for the Nintendo 64 in Japan on 27 April 2000 and in North America on 26 October the same year. The seventy-two hours before the moon falls, about fifty-four minutes of real time, can be rewound with the Song of Time. The rewind costs consumables and errands in progress, but masks, learned songs and proof of cleared dungeons remain. The Bombers' Notebook, which records the townspeople's daily schedules, was there from the start as a tool for keeping knowledge outside the player's head.
Outer Wilds (2019) pared the skeleton down the furthest. Every piece of equipment is present on the first lap, and there are no upgrades at all. What blocks the way inward is ignorance rather than ability, so a player who already knew everything could in theory reach the ending in the first twenty-two minutes.
The name came later. This family is informally called a metroidbrainia, and the earliest recorded use is a post of 18 September 2015 in which Nick Suttner applied the word to The Witness. It covers knowledge-gated design in general, not time loops alone.
The same skeleton exists on the table. In T.I.M.E Stories (2015, Space Cowboys, designed by Manuel Rozoy and Peggy Chassenet), running out of Temporal Units sends the agents back to the start of the same case. The board resets; the players' memory does not. As a narrative shape the film Groundhog Day (1993) is the widely known reference, but the first game to use it cannot be pinned down.
Variations
The length of one lap decides the feel. Twelve Minutes runs twelve minutes, Outer Wilds twenty-two, The Sexy Brutale twelve in-game hours, Majora's Mask three days. The shorter the lap, the cheaper one experiment is and the faster hypotheses can be tried. The longer it is, the thicker the world becomes, but the heavier the re-run needed to reach the one thing you wanted to check.
Change how knowledge is gathered and the same mechanic becomes a different game. The Sexy Brutale turns a whole mansion into clockwork and makes the player watch the procedure through keyholes. The Forgotten City leans on dialogue, so that a fact drawn out of a resident becomes the next conversation option. Twelve Minutes shrinks the world to one apartment, where knowing a particular word turns the same conversation into a different door.
The loop can be joined to things other than exploration and deduction. Minit (2018) makes a sixty-second death-and-reset continuous with the exploration of a wide landscape. Overboard! (2021, inkle) reverses the position and puts the player on the culprit's side. What is collected is not the truth, but the sequence of moves needed to hang one's own crime on somebody else.
Design pitfalls
The largest pitfall is that re-running a procedure you already understand becomes dull. Quality shows in how much known repetition the design manages to subtract. Majora's Mask skips time with songs, The Sexy Brutale rewinds to noon with a pocket watch, and The Forgotten City supplies shortcuts and summaries of conversations already heard. A loop whose re-runs are heavy stalls on the second lap, however beautiful the world.
Second, a stretch that tests execution rather than knowledge breaks the rule the mechanic set for itself. The counter-take on Outer Wilds points out that failing the endgame procedure burns ten minutes or more while adding no knowledge at all. Waiting is friction of the same kind. Time spent sitting until something happens is time in which nothing is learned.
Third, the design can fail to make the player form a question. A knowledge gate has to be built as a device that provokes questions, not one that hides answers. A player released into a wide world with no question in mind is driven into brute-force interrogation. Where the notes are kept is the same problem: as the design of in-game notebooks argues, a game whose progress exists only in the player's head can have hours of it overwritten by a single spoiler.
How to tell it apart
The difference from time manipulation is who moves time. In time manipulation the player uses rewind or pause as a tool and assembles causality from the back. In a time loop the player cannot move time at all; time resets itself to its initial value. The two can overlap: the Song of Time in Majora's Mask is a single piece of time manipulation placed inside a loop.
Deduction and searching the archive overlap here, because knowledge is the progress in all three. The test is whether the world state periodically returns to its initial value. In the record-reading games the world does not return; the player simply catches up late. What escape rooms and puzzle boxes close off is space, whereas what this mechanic closes off is time.
Further reading
On this site. The overview is Solving the time loop — when knowledge is the only save file. For a critical reading, the counter-take on Outer Wilds. On where the player is made to write things down, the design of in-game notebooks.
Neighbouring questions. On whether choice means anything in a world you can redo, does choice matter when you can undo?; on the weight of knowing, if you looked it up, did you solve it?; on showing dead ends, legible failure. From the music side, the soundtracks of The Sexy Brutale and Minit; for a short introduction, drawer of the day #17; from the market side, the map of Mystlike that Thinky Games draws.
Outside sources. The release dates, the seventy-two-hour cycle and the list of items carried across resets in Majora's Mask follow the English Wikipedia article. The first use of metroidbrainia is the 18 September 2015 post by Nick Suttner, cited in Kate Gray's Nintendo Life feature of 20 May 2022. The Temporal Unit and "run" structure of T.I.M.E Stories follows the Meeple Mountain review.
See also
Time Manipulation / Deduction / Searching the Archive / Environmental Observation / Escape Rooms & Puzzle Boxes
