Minecraft seeds: reproducing a world correctly

A seed is the value used to generate a world. It does not contain buildings created by players. If you want an already built city or an adventure, look for a downloadable map rather than a seed.

Record the seed together with the edition, game version and generation settings. A world generated with mods or a custom datapack may look different when the same seed is used in an unmodified game.

Check interesting locations in a separate test world before starting a long survival project. Note the coordinates as well as the seed, and keep the generation settings unchanged if you want to reproduce the result.