On many laptops the function keys need the Fn key as well, so the combination becomes Fn + F3 + G.
Find your chunk on the debug screen
Press F3 on its own to open the debug screen. The Chunk line shows your position inside the chunk and the chunk coordinates. The Block line shows the whole-number block you’re standing on, which is the number to use in the Chunk Calculator.
Build machines inside one chunk
The game loads and unloads whole chunks. When a player moves away, one chunk can unload while its neighbour stays loaded for a moment longer. Anything that crosses the border is at risk:
- Redstone clocks and contraptions can stop half-way and get stuck.
- Item sorters and hopper lines can back up when part of the line unloads.
- Farms that rely on pistons or water flow can break mid-cycle.
With borders visible, it is easy to keep a compact machine within a single 16 × 16 area.
Chunks for slime farms
Slimes spawn below Y 40 in slime chunks, which are chosen by the world seed in Java Edition. Once you have found one, show the borders so the spawning platforms cover exactly that chunk and nothing outside it.
Without F3
Bedrock Edition has no chunk border display. Divide your X and Z by 16 and round down, or enter the coordinates in the Chunk Calculator, which also lists the chunk’s first and last block in both directions.
The guide to how chunks work explains what keeps chunks loaded now that Java Edition 1.21.9 has removed spawn chunks.