Minecraft wiki entry for Spawner, associated text: The spawner attempts to spawn 4 mobs at randomly chosen points within the spawning volume, then wait anywhere from 200 to 799 ticks (10 to 39.95 seconds) before spawning again. As it waits, the mob inside the block spins faster and faster. Except for spawning on a solid block, all of the usual requirements for spawning must be met (not in a solid block, correct light level, etc.), so the spawner often produces fewer than 4 mobs. When it does spawn, it emits a "poof", and more flame particles temporarily appear around it. If the spawner fails to spawn any mobs because it did not pick any suitable locations, it repeats this process every tick until it succeeds. It starts waiting for the next cycle after it spawns at least one mob. If, at the time of spawning, 6 or more mobs of the spawner's type are present within a 9×9×9 volume centered on the spawner block (in Java Edition) or a 16×10×16 volume centered on the lower northwest corner of the spawner block (in Bedrock Edition), the spawner "poofs" without creating any mobs and then waits for the next cycle.