Minecraft Version Numbers & pack_format, Explained

Every datapack and resource pack declares a 'pack_format' — an integer that tells Minecraft which version of the data layout the pack was written for. Mojang bumps this number whenever they change the internal structure of packs (renaming a folder, changing a JSON schema, and so on). When the game's expected format and the pack's declared format don't match, you get the dreaded 'incompatible' warning, or the pack silently does nothing.

Why the number keeps changing

Think of pack_format as a compatibility contract. A pack built for an older layout might reference a folder that no longer exists, or use a JSON field the new game ignores. Rather than guess, Minecraft checks the declared format up front. This is good for stability — but it means a pack made for one version can need a small tweak to load on the next.

Modern Minecraft makes this friendlier in two ways. First, packs can declare a supported range instead of a single number, so one pack can cover several versions. Second, the game shows a clear warning instead of failing silently, so you know to update.

Best practices that avoid format headaches

• ▸Always set pack_format to match the Minecraft version you're actually playing on.
• ▸When a tool offers it, declare a supported range (a minimum and a generous maximum) so the pack survives future updates.
• ▸Keep one pack per major version line if you support very old and very new versions at once — it's cleaner than fighting one pack to cover everything.
• ▸After a Minecraft update, re-test your packs before assuming they still work; a format bump is the usual culprit when something breaks.

Let the tool handle it

Tracking pack_format numbers by hand is tedious and easy to get wrong. Mine Mod AI keeps an up-to-date map of Minecraft versions to pack_format values and writes the correct number — plus a wide compatibility range where the game supports it — into every pack it generates, so the output loads on the version you picked without you memorising a single number.