Why Won't It Spawn

# Why Won't It Spawn

Stand where a structure should be and ask why it isn't.

```
/whynot structure minecraft:pillager_outpost
```

```
--- why not minecraft:pillager_outpost ---
you are standing in: biomesoplenty:prairie
This biome is NOT in the structure's biome list. It cannot generate here.
The list comes from the tag: #minecraft:has_structure/pillager_outpost

FOUND IT: 'mod/t_and_t' declared "replace": true on that tag,
which deleted every entry the packs below it had added - including yours.
The game does not log this. Nothing crashes; the entry is simply gone.

Other mods lost entries here too (14), and were never told either:
    biomesoplenty:lush_desert
    biomesoplenty:prairie
    #terralith:reference/forest
    ... and 11 more

It also dropped 6 of vanilla's own entries.
That part is probably deliberate - redefining a vanilla list is what
"replace" is for, and the mod likely substitutes its own version. Not a bug.
```

That is a real answer from a real pack. Install **Towns & Towers**, **Biomes O' Plenty** and
**Terralith** together - all three excellent, all three perfectly correct on their own - and six BOP
biomes quietly lose every pillager outpost there is. Nothing in the log. Nothing crashes. The
structure just never appears, and you have no thread to pull.

## Why this needs a mod

A biome tag is normally *merged*: every mod adds its biomes to the pile and nobody loses. But a mod
can write `"replace": true`, and then the tag loader throws away everything the mods below it
contributed. Silently. The mod that lost its entries is not named in the replacer's file and is never
told.

By the time the game has finished loading, those entries are **gone**. There is nothing left to
inspect - which is why you cannot find this yourself. The evidence only exists in the individual
packs' files, before they are merged. That is what this reads.

## What it will NOT do

**It will not call a mod broken for redefining a vanilla list.** That is exactly what `replace` is
for, and a mod doing it usually ships its own replacement - Towns & Towers substitutes its own
per-biome outposts for the vanilla ones it removes. Vanilla losses are reported separately and
labelled as probably deliberate.

**It will not accuse anyone when your biome was simply never in the tag.** "Nobody added it" and
"somebody deleted it" are different answers, and confusing them gets innocent mods bug reports. If
your biome was never listed, it says so, and calls it what it is: a missing compat patch.

Both rules were learned the hard way. An earlier version of the sibling project reported Towns &
Towers as broken when it was not.

## Fixing what it finds

- **Tag Rescue** puts other mods' entries back, keeping the replacer's own edit intact.
- Or add your biome to the tag yourself with a data pack.
- Or ask the mod to use `"replace": false`.

Load order will **not** fix it. You want both lists merged; reordering only picks a different winner.

## Notes

- Server side (commands live on the server). Safe on a client too.
- No dependencies. No mixins. Changes no behaviour - it only reads.
- MIT licensed.