Stronghold Finder
Edition
Version
Seed
On rings around 0, 0: three in the first ring, then more in each ring further out. The map works out each one's exact chunk, including the nudge every stronghold takes toward a valid biome.
It shows the stronghold's starting chunk. The portal room is somewhere in the stronghold's corridors, usually close by and deep underground.
On Java Edition, type /seed in chat (it needs cheats on, or operator rights on a server). On Bedrock, open the world's settings: the seed is listed under Game.