The default dimension JSON for the nether in Minecraft.

nether.json

{
  "type": "minecraft:the_nether",
  "generator": {
    "biome_source": {
      "humidity_noise": {
        "firstOctave": -7,
        "amplitudes": [
          1.0,
          1.0
        ]
      },
      "altitude_noise": {
        "firstOctave": -7,
        "amplitudes": [
          1.0,
          1.0
        ]
      },
      "weirdness_noise": {
        "firstOctave": -7,
        "amplitudes": [
          1.0,
          1.0
        ]
      },
      "seed": 0,
      "biomes": [
        {
          "parameters": {
            "altitude": 0.0,
            "weirdness": 0.0,
            "offset": 0.0,
            "temperature": 0.0,
            "humidity": 0.0
          },
          "biome": "minecraft:nether_wastes"
        },
        {
          "parameters": {
            "altitude": 0.0,
            "weirdness": 0.0,
            "offset": 0.0,
            "temperature": 0.0,
            "humidity": -0.5
          },
          "biome": "minecraft:soul_sand_valley"
        },
        {
          "parameters": {
            "altitude": 0.0,
            "weirdness": 0.0,
            "offset": 0.0,
            "temperature": 0.4,
            "humidity": 0.0
          },
          "biome": "minecraft:crimson_forest"
        },
        {
          "parameters": {
            "altitude": 0.0,
            "weirdness": 0.0,
            "offset": 0.375,
            "temperature": 0.0,
            "humidity": 0.5
          },
          "biome": "minecraft:warped_forest"
        },
        {
          "parameters": {
            "altitude": 0.0,
            "weirdness": 0.0,
            "offset": 0.175,
            "temperature": -0.5,
            "humidity": 0.0
          },
          "biome": "minecraft:basalt_deltas"
        }
      ],
      "temperature_noise": {
        "firstOctave": -7,
        "amplitudes": [
          1.0,
          1.0
        ]
      },
      "type": "minecraft:multi_noise"
    },
    "seed": 0,
    "settings": "minecraft:nether",
    "type": "minecraft:noise"
  }
}