Java Edition datapacks as a format and as a source of vanilla data
Researched 2026-10-24 against Mojang's own files: the Java Edition 26.3 server jar and its data generator (also run for 1.21.11, 26.1 and 26.2 to date one change), the piston-meta version manifest, Mojang's Java changelogs on minecraft.net, the EULA, and two republishers (misode/mcmeta, PrismarineJS/minecraft-data) for their own statements. The Bedrock side comes from bedrock-data-extraction.md and is not repeated.
Summary
- The current Java release is 26.3 (2026-09-15, data pack version 121.0, Java 25). Its data generator runs in 8 seconds and writes the full vanilla datapack (10038 files, 34 MB) plus reports. Command and hashes are in "Reproduction".
- A datapack can carry 60 element registries plus functions and structures; 95 further registries accept only tags and are defined in code.
reports/datapack.jsonis Mojang's own list of both sets. reports/blocks.jsoncarries no block properties. Stone is{"states": [{"default": true, "id": 1}]}. Thedefinitionfield (a class name such asminecraft:stairplus constructor arguments) existed from 1.20.5 through 26.2 with an always-emptypropertiesobject, and 26.3 removed it. No Mojang report has ever listed hardness, blast resistance, friction, light, map color, sound type or tool requirements per block. 26.2's lastdefinitiondump names 265 block classes for 1196 blocks.- Default item components are complete: 1658 items, one file each under
reports/minecraft/components/item/, withmax_stack_size,max_damage,tool,food,consumable,attribute_modifiers,equippable,repairable,enchantable,weaponand so on, 122 component types in the registry. - Entities have no data definitions. 161 entity types, 40 attributes, 115 memory modules and 24 sensors are code. Only variants (cat, wolf, pig, cow, chicken, frog, zombie nautilus) and biome spawn lists are data.
- Java worldgen is data in full: 7 noise settings, 55 density functions over 44 operator types (33 used), 64 noises, 67 biomes, 7594 multi-noise parameter points, 240 configured and 273 placed features over 58 feature types (47 used) and 18 placement modifiers (15 used), 4 carvers over 2 types, 52 structures over 16 types, 21 structure sets, 245 template pools, 40 processor lists, 1511 structure NBT files.
- Loot (1447 tables, 42 modifier types), recipes (2042, 22 serializers, brewing since 26.3), tags (883 files in 16 registries), advancements (1866), enchantments (43, with 31 effect component types), damage types (51), villager trades (391 trades, 68 trade sets, since 26.1), timelines and world clocks (26.1), environment attributes (1.21.11) are data.
- Identifiers: 1102 of Java's 1286 block names also exist in the Bedrock 1.26.51 palette (1477 names); 1565 of Java's 1658 item names exist in Bedrock's 2076-entry item table. The differences are systematic (Bedrock
*_double_slab,*_standing_sign,element_*,lit_*,light_block_*; Javapotted_*,*_wall_banner,*_bed,*_wall_sign). - Licensing is the same EULA as Bedrock. misode/mcmeta has no license file and says "If Mojang ever has something against this data existing here, the repository will be promptly removed." PrismarineJS/minecraft-data's README says "MIT" and has no LICENSE file at its current master commit.
- For a Bedrock server, Java datapacks are the richer format for terrain, biomes, features, structures, loot, enchantments and item components; Bedrock behavior packs are the richer format for entities (all 130 as JSON), spawn rules and the 98 data-driven blocks. Neither edition defines block behavior or block properties in data.
1. The datapack format in 26.3
Pack metadata
version.json inside the server jar (unzip -p server.jar version.json):
{"id": "26.3", "name": "26.3", "world_version": 5023, "series_id": "main", "protocol_version": 777,
"pack_version": {"resource_major": 97, "resource_minor": 1, "data_major": 121, "data_minor": 0},
"build_time": "2026-09-15T11:20:48+00:00", "java_component": "java-runtime-epsilon", "java_version": 25, "stable": true, "use_editor": false}The data pack version is 121.0. The 1.21.9 changelog (https://www.minecraft.net/en-us/article/minecraft-java-edition-1-21-9) describes the current pack.mcmeta: "The pack versions for data packs and resource packs now have minor versions. A minor version increment of the game's pack version is backwards-compatible"; "The supported_formats field has been removed"; "The pack_format field is now optional"; "Added required field min_format - specifies the minimum version supported. A full version is specified as a list of two integers, e.g. [74, 1]. Specifying a single integer is interpreted as that major version". The three built-in packs in the 26.3 jar use the integer form, for example data/minecraft/datapacks/trade_rebalance/pack.mcmeta:
{"features": {"enabled": ["minecraft:trade_rebalance"]},
"pack": {"description": {"translate": "dataPack.trade_rebalance.description"}, "max_format": 121, "min_format": 121}}The server jar carries no root pack.mcmeta for the vanilla pack itself; the three built-in packs (trade_rebalance, redstone_experiments, minecart_improvements) are the only ones. misode/mcmeta's data branch writes one as {"pack": {"description": "The default data for Minecraft", "pack_format": 125, "min_format": [125, 0], "max_format": [125, 0]}} (for the 26.4 snapshot at its head).
What a datapack can carry
reports/datapack.json lists every registry with elements (whether a datapack can add entries), tags and stable. In 26.3 it has 155 registries: 60 with elements: true, 95 with elements: false, plus two "others" (function, format mcfunction, and structure, format structure). The 60 element registries, with the vanilla file count from data/minecraft/ and what the JSON parameterizes:
| Folder | Files | What the data decides | What stays Java code |
|---|---|---|---|
advancement | 1866 (1740 under recipes/) | criteria from 58 trigger types, rewards, display | the trigger implementations |
banner_pattern, decorated_pot_pattern, trim_pattern, trim_material, painting_variant, jukebox_song, instrument | 43, 23, 18, 11, 51, 22, 8 | asset ids, translation keys, song length, horn range | rendering, playback |
block_transformer (26.3) | 3 | axe strip, shovel path, hoe till as block_state_provider rules | the interaction that invokes them |
cat_variant, wolf_variant, pig_variant, cow_variant, chicken_variant, frog_variant, zombie_nautilus_variant and *_sound_variant | 11, 9, 3, 3, 3, 3, 2 and 2 to 7 | texture ids and spawn_conditions (structure, moon_brightness, biome) | everything else about the mob |
chat_type | 7 | translation key and parameters | |
context_int_provider, context_float_provider (26.3) | 26, 4 | named numbers such as brewing uses, compost chances, looked up by loot and recipes | |
damage_type | 51 | exhaustion, message_id, scaling, effects | which code path deals which type |
dialog | 3 | server-driven UI screens | |
dimension, dimension_type | 0, 4 | height, light rules, coordinate scale, attributes, timelines, default_clock | |
enchantment, enchantment_provider | 43, 7 | cost curves, slots, exclusivity, effects over 31 effect component types (30 used) | the effect component implementations |
item_modifier, predicate | 0, 3 | loot functions and conditions as standalone files | |
loot_table | 1447 | pools, entries (9 types), 42 modifier types, 20 condition types | the implementations |
recipe | 2042 | 22 serializers including brewing (279 files, new in 26.3) | 8 crafting_special_* serializers are code with a data stub |
slot_source (26.3) | 0 | slot selection for /item | |
sulfur_cube_archetype | 12 | attribute modifiers for the 26.x sulfur cube mob | |
test_environment, test_instance | 1, 1 | GameTest setup | the test functions |
timeline, world_clock (26.1) | 4, 2 | day cycle markers and attribute tracks | |
trade_set, villager_trade (26.1) | 68, 391 | wants, gives, max_uses, reputation_discount; sets reference tags | |
trial_spawner | 28 | spawn potentials, counts per player, cooldowns | |
worldgen/* | 1144 | section 4 | the chunk generator, carvers, feature and density function implementations |
The 95 elements: false registries are code, and a datapack may only tag them: activity, attribute, block, block_entity_type, entity_type, fluid, game_event, game_rule, item, memory_module_type, mob_effect, particle_type, potion, sensor_type, sound_event, villager_profession, villager_type, every *_type registry (feature_type, density_function_type, loot_function_type, data_component_type, trigger_type and so on). Tags ship for 16 registries: block 300 files, item 236, worldgen/* 123, villager_trade 73, entity_type 49, damage_type 36, enchantment 22, banner_pattern 11, fluid 10, game_event 5, potion 5, timeline 4, instrument 3, point_of_interest_type 3, dialog 2, painting_variant 1.
Structures are NBT, not JSON: the jar has 1511 files under data/minecraft/structure/, and the generator does not re-emit them (its --all output has no structure folder).
2. Running Mojang's data generator
Finding and fetching the jar
https://net-secondary.web.minecraft-services.net/api/v1.0/download/links returns serverJar = https://piston-data.mojang.com/v1/objects/33680f5f2ac32864d6d7cf5e56a705fdb3e05f4c/server.jar. The launcher manifest https://piston-meta.mojang.com/mc/game/version_manifest_v2.json has latest.release = 26.3 and latest.snapshot = 26.4-snapshot-5; the 26.3 entry points at https://piston-meta.mojang.com/v1/packages/61fff1316bd50312624a858bbb5eb18fa45208ed/26.3.json, whose downloads.server is the same URL with sha1 33680f5f2ac32864d6d7cf5e56a705fdb3e05f4c, size 62294556, and whose javaVersion is {"component": "java-runtime-epsilon", "majorVersion": 25}. The downloaded file matched: sha1 33680f5f..., sha256 d052f14d7a173734fba553711e5b570162e2f2a313267ee31a21b975a679be64, 62294556 bytes. Earlier releases resolve the same way (1.21.11 64bb6d76..., 26.1 3872a7f0..., 26.2 823e2250..., all needing Java 21 or 25 per their manifests).
The jar is a bundler (META-INF/MANIFEST.MF: Main-Class: net.minecraft.bundler.Main, Bundler-Format: 1.0; META-INF/main-class: net.minecraft.server.Main; META-INF/versions.list: 26.3/server-26.3.jar). On first run it unpacks versions/26.3/server-26.3.jar and 39 libraries into the working directory.
Invocation
The machine had Java 21 on PATH and Oracle GraalVM 25.0.4 at /Library/Java/JavaVirtualMachines/graalvm-25.jdk/Contents/Home. With Java 25:
java -DbundlerMainClass=net.minecraft.data.Main -jar server.jar --help
Option Description
--all Include all generators
--dev Include development tools
--help Show the help menu
--input <String> Input folder
--output <String> Output folder (default: generated)
--reports Include data reports
--server Include server generators
--validate Validate inputsjava -DbundlerMainClass=net.minecraft.data.Main -jar server.jar --reports --server --all --output <dir> logged All providers took: 3997 ms and Caching: total files: 10038 ... written: 10038; wall time 8.0 s including unpacking. Adding --dev produced an identical file list. The providers are vanilla/Block List, vanilla/Default Components, vanilla/Command Syntax, vanilla/Registry Dump, vanilla/Packet Report, vanilla/Datapack Structure, vanilla/Json RPC API schema, vanilla/Biome Parameters, vanilla/Registries for world, vanilla/Registries for reloadable, 20 vanilla/Tags for *, and the pack metadata, registry and tag providers of the three built-in packs. This matches misode/mcmeta's README, which names the same command.
Output: data/ (34 MB) and reports/ (18 MB): blocks.json 7330564 B, commands.json 583592 B, registries.json 536272 B, datapack.json, packets.json (144 clientbound and 69 serverbound play packets), json-rpc-api-schema.json, biome_parameters/minecraft/{overworld,nether}.json, and minecraft/components/item/*.json (1658 files). There is no reports/items.json since 26.1: "The report generator for item components has been renamed to "Default Components" and now outputs one file for each element that has default components" (https://www.minecraft.net/en-us/article/minecraft-java-edition-26-1). 1.21.11 still wrote items.json with 1505 entries.
reports/blocks.json: states only, no properties
1286 blocks, 35723 states. Each entry has properties (name to allowed values) and states (each with id, properties, and default: true on one). Verbatim:
"minecraft:stone": {"states": [{"default": true, "id": 1}]}"minecraft:oak_stairs": {
"properties": {"facing": ["north", "south", "west", "east"], "half": ["top", "bottom"],
"shape": ["straight", "inner_left", "inner_right", "outer_left", "outer_right"], "waterlogged": ["true", "false"]},
"states": [{"id": 5463, "properties": {"facing": "north", "half": "top", "shape": "straight", "waterlogged": "true"}},
... 38 more ...
{"default": true, "id": 5474, "properties": {"facing": "north", "half": "bottom", "shape": "straight", "waterlogged": "false"}},
...]}There is no definition key in 26.3. The 26.3 changelog (https://www.minecraft.net/en-us/article/minecraft-java-edition-26-3) says: "The definition field from the blocks.json data generation report has been removed". Running the same generator on 1.21.11, 26.1 and 26.2 shows what it was:
"minecraft:stone": {"definition": {"type": "minecraft:block", "properties": {}}, "states": [...]}
"minecraft:oak_stairs": {"definition": {"type": "minecraft:stair", "base_state": {"Name": "minecraft:oak_planks"}, "properties": {}}, ...}
"minecraft:oak_door": {"definition": {"type": "minecraft:door", "block_set_type": "oak", "properties": {}}}
"minecraft:chest": {"definition": {"type": "minecraft:chest", "close_sound": "minecraft:block.chest.close", "open_sound": "minecraft:block.chest.open", "properties": {}}}
"minecraft:water": {"definition": {"type": "minecraft:liquid", "fluid": "minecraft:water", "properties": {}}}
"minecraft:sand": {"definition": {"type": "minecraft:sand", "falling_dust_color": "#00dbd3a0", "properties": {}}}
"minecraft:oak_leaves": {"definition": {"type": "minecraft:tinted_particle_leaves", "leaf_particle_chance": 0.01, "properties": {}}}In all three versions definition.properties was {} for every one of the 1166 to 1196 blocks. The report never carried hardness, explosion resistance, friction, light emission, map color, sound type or requires_correct_tool_for_drops; those are BlockBehaviour.Properties in code and no Mojang output lists them. What the definition did give was the block class and its constructor arguments: 263 distinct type values in 1.21.11, 265 in 26.2. The extra keys per class in 26.2: color 112, block_set_type 72, weathering_state 68, base_state 64, wood_type 60, potted 39, dead 20, candle 17, concrete 16, experience 16, suspicious_stew_effects 15, ticks_to_stay_pressed 14, leaf_particle_chance 11, tree 9, close_sound 9, open_sound 9, kind 9, host 7, support_blocks 6, feature 6, particle_options 6, and 26 rarer ones.
The 265 block classes of 26.2 (count of blocks using each), which is Java's inventory of block behaviors:
block 181, slab 64, stair 60, rotated_pillar 56, flower_pot 39, wall 32, candle 17, candle_cake 17, door 17, shulker_box 17, trapdoor 17, banner 16, bed 16, concrete_powder 16, drop_experience 16, glazed_terracotta 16, stained_glass 16, stained_glass_pane 16, wall_banner 16, wool_carpet 16, button 14, flower 14, pressure_plate 14, fence 13, ceiling_hanging_sign 12, fence_gate 12, shelf 12, standing_sign 12, wall_hanging_sign 12, wall_sign 12, weathering_copper_full 12, sapling 8, infested 6, iron_bars 6, lantern 6, tinted_particle_leaves 6, base_coral_fan 5, base_coral_plant 5, base_coral_wall_fan 5, chain 5, coral 5, coral_fan 5, coral_plant 5, coral_wall_fan 5, skull 5, amethyst_cluster 4, copper_bulb_block 4, copper_chest 4, copper_golem_statue 4, lightning_rod 4, tall_flower 4, untinted_particle_leaves 4, wall_skull 4, waterlogged_transparent 4, weathering_copper_bar 4, weathering_copper_bulb 4, weathering_copper_chain 4, weathering_copper_chest 4, weathering_copper_door 4, weathering_copper_golem_statue 4, weathering_copper_grate 4, weathering_copper_slab 4, weathering_copper_stair 4, weathering_copper_trapdoor 4, weathering_lantern 4, weathering_lightning_rod 4, air 3, anvil 3, command 3, double_plant 3, huge_mushroom 3, torch 3, wall_torch 3, attached_stem 2, azalea 2, beehive 2, bonemealable_feature_placer 2, brushable 2, campfire 2, eyeblossom 2, flower_bed 2, jack_o_lantern 2, layered_cauldron 2, liquid 2, mushroom 2, nether_fungus 2, nether_roots 2, nylium 2, piston_base 2, powered_rail 2, redstone_ore 2, sand 2, stem 2, tall_grass 2, weighted_pressure_plate 2, and 162 single-block classes: amethyst, bamboo_sapling, bamboo_stalk, barrel, barrier, beacon, beetroot, bell, big_dripleaf, big_dripleaf_stem, blast_furnace, brewing_stand, bubble_column, budding_amethyst, bush, cactus, cactus_flower, cake, calibrated_sculk_sensor, carpet, carrot, cartography_table, cauldron, cave_vines, cave_vines_plant, chest, chiseled_book_shelf, chorus_flower, chorus_plant, cocoa, colored_falling, comparator, composter, conduit, crafter, crafting_table, creaking_heart, crop, crying_obsidian, daylight_detector, decorated_pot, detector_rail, dirt_path, dispenser, dragon_egg, dried_ghast, dropper, dry_vegetation, enchantment_table, end_gateway, end_portal, end_portal_frame, end_rod, ender_chest, farmland, fire, firefly_bush, frogspawn, frosted_ice, furnace, glow_lichen, grass, grindstone, half_transparent, hanging_moss, hanging_roots, hay, heavy_core, honey, hopper, ice, infested_rotated_pillar, jigsaw, jukebox, kelp, kelp_plant, ladder, lava_cauldron, leaf_litter, lectern, lever, light, lily_pad, loom, magma, mangrove_leaves, mangrove_propagule, mangrove_roots, mossy_carpet, moving_piston, mud, multiface, mycelium, nether_portal, nether_sprouts, nether_wart, netherrack, note, observer, piglinwallskull, piston_head, pitcher_crop, player_head, player_wall_head, pointed_dripstone, potato, potent_sulfur, powder_snow, powered, pumpkin, rail, redstone_lamp, redstone_torch, redstone_wall_torch, redstone_wire, repeater, respawn_anchor, rooted_dirt, scaffolding, sculk, sculk_catalyst, sculk_sensor, sculk_shrieker, sculk_vein, sea_pickle, seagrass, short_dry_grass, slime, small_dripleaf, smithing_table, smoker, sniffer_egg, snow_layer, snowy_dirt, soul_fire, soul_sand, spawner, sponge, spore_blossom, stonecutter, structure, structure_void, sugar_cane, sulfur_spike, sweet_berry_bush, tall_dry_grass, tall_seagrass, target, test, test_instance, tinted_glass, tnt, torchflower_crop, transparent, trapped_chest, trial_spawner, trip_wire_hook, tripwire, turtle_egg, twisting_vines, twisting_vines_plant, vault, vine, web, weeping_vines, weeping_vines_plant, wet_sponge, wither_rose, wither_skull, wither_wall_skull.
Only 181 of 1196 blocks are the plain block class; 1015 blocks use one of 264 specialized classes. Bedrock's internal_vanilla_data.block_archetype in its 98 block files (slab_block, stair_block, wall_foliage_block) is the same idea with three public names.
Default item components: complete
1658 files, one per item in the minecraft:item registry (1658 entries). Verbatim, reports/minecraft/components/item/diamond_pickaxe.json:
{"components": {
"minecraft:attack_animation": {},
"minecraft:attribute_modifiers": [
{"type": "minecraft:attack_damage", "amount": 4.0, "id": "minecraft:base_attack_damage", "operation": "add_value", "slot": "mainhand"},
{"type": "minecraft:attack_speed", "amount": -2.799999952316284, "id": "minecraft:base_attack_speed", "operation": "add_value", "slot": "mainhand"}],
"minecraft:break_sound": "minecraft:entity.item.break",
"minecraft:damage": 0,
"minecraft:enchantable": {"value": 10},
"minecraft:enchantments": {},
"minecraft:interact_animation": {},
"minecraft:item_model": "minecraft:diamond_pickaxe",
"minecraft:item_name": {"translate": "item.minecraft.diamond_pickaxe"},
"minecraft:lore": [],
"minecraft:max_damage": 1561,
"minecraft:max_stack_size": 1,
"minecraft:rarity": "common",
"minecraft:repair_cost": 0,
"minecraft:repairable": {"items": "#minecraft:diamond_tool_materials"},
"minecraft:tool": {"rules": [
{"blocks": "#minecraft:incorrect_for_diamond_tool", "correct_for_drops": false},
{"blocks": "#minecraft:mineable/pickaxe", "correct_for_drops": true, "speed": 8.0}]},
"minecraft:tooltip_display": {},
"minecraft:use_effects": {},
"minecraft:weapon": {"item_damage_per_attack": 2}}}apple.json:
{"components": {
"minecraft:attack_animation": {}, "minecraft:attribute_modifiers": [], "minecraft:break_sound": "minecraft:entity.item.break",
"minecraft:compostable": {"layers": "minecraft:compostable/medium"},
"minecraft:consumable": {},
"minecraft:enchantments": {},
"minecraft:food": {"nutrition": 4, "saturation": 2.4},
"minecraft:interact_animation": {}, "minecraft:item_model": "minecraft:apple", "minecraft:item_name": {"translate": "item.minecraft.apple"},
"minecraft:lore": [], "minecraft:max_stack_size": 64, "minecraft:rarity": "common", "minecraft:repair_cost": 0,
"minecraft:tooltip_display": {}, "minecraft:use_effects": {}}}The data_component_type registry has 122 entries. Thirteen appear on every item (attack_animation, attribute_modifiers, break_sound, enchantments, interact_animation, item_model, item_name, lore, max_stack_size, rarity, repair_cost, tooltip_display, use_effects); the rest are present only where they apply. Tool speed is a tag lookup: tags/block/mineable/pickaxe.json has 449 values, and incorrect_for_wooden_tool is ["#minecraft:needs_diamond_tool", "#minecraft:needs_iron_tool", "#minecraft:needs_stone_tool"]. Base break time still needs the block's hardness, which is in code (above).
Everything else in reports/
registries.json has 95 registries with protocol_id per entry; minecraft:block 1286, minecraft:item 1658, minecraft:entity_type 161, minecraft:block_entity_type 49, minecraft:sound_event 1991, minecraft:particle_type 128, minecraft:mob_effect 40, minecraft:potion 46, minecraft:attribute 40, minecraft:game_rule 59. commands.json is the Brigadier tree with 94 root commands. biome_parameters/minecraft/overworld.json expands the minecraft:overworld multi-noise preset into 7594 parameter points over 56 biomes; nether.json has 5 points over 5 biomes.
misode/mcmeta as a fallback
Not needed here, but checked. git ls-remote https://github.com/misode/mcmeta on 2026-10-24: data = 991b9973a3a2930b5240dba6a39b1f2eb1f11eca, summary = f41a317b67b4e08155bf8b2ac3e853516d1fd889, registries = 0fdeca63f4a6350d84bafc9b7e00f13109f32f4e; per-version tags 26.3-data = 538b2b167248c648b2198f2c0d56eced10dfc0cf, 26.3-summary = d96c75fec200c4580dd75e033a76341521165461, 26.3-registries = 2240df2376509bfaf12becbb36e156e29f8ecb4d. The summary head's version.json is 26.4-snapshot-5 with data_pack_version 125. Its README "Sources": "Version manifest ... client and server jars by following links", "Data generator using the following commands (depending on version): java -cp server.jar net.minecraft.data.Main --reports, java -DbundlerMainClass=net.minecraft.data.Main -jar server.jar --reports", and "Slicedlime's examples repo for worldgen changes before 1.18-pre1". Its summary/blocks/data.json is a condensed state table and its summary/item_components/data.json is "The default item components added in 1.20.5"; neither adds anything the generator does not emit.
3. What is not data-driven in Java
Blocks
Block identity (the registry), block states (property names, values, order, numeric ids), and block properties (hardness, resistance, friction, light, map color, sound, tool requirement, collision shape) are code. The datapack cannot add, remove or alter a block; minecraft:block is elements: false in datapack.json. What data touches blocks: loot tables (1201 loot_table/blocks/*.json), tags (300 files, including mineable/*, needs_*_tool), block_transformer (3 files for axe, shovel, hoe), and worldgen. The client-side assets/minecraft/blockstates/*.json maps states to models and is rendering, not behavior.
Entities
minecraft:entity_type is elements: false. There is no entity folder in data/minecraft/. The AI registries are code: attribute 40 (max_health, movement_speed, attack_damage, follow_range, scale, ...), memory_module_type 115, sensor_type 24, activity 26, entity_sub_predicate_type 25. The data-side entity surface is: variant registries with spawn_conditions (for example cat_variant/all_black.json spawns at moon_brightness 0.9 or in #minecraft:cats_spawn_as_black structures), sulfur_cube_archetype (attribute modifiers for one mob), trial_spawner, biome attributes.minecraft:gameplay/natural_mob_spawns (weights, group sizes, spawn costs), and loot (109 loot_table/entities/*.json). Entity dimensions, drops-by-code (experience), goals and brains are Java.
Items
Components were introduced in snapshot 24w09a and release 1.20.5: "We are making some large changes to how Item Stack-specific properties are stored and represented in this snapshot, replacing the current NBT 'tag' with structured components" and "Default component values for items are now listed in items.json generated in reports" (https://www.minecraft.net/en-us/article/minecraft-snapshot-24w09a and https://www.minecraft.net/en-us/article/minecraft-java-edition-1-20-5). Later additions, each from the named release article on minecraft.net:
- 1.21.2 (
.../minecraft-java-edition-1-21-2), "New Item Components":consumable,use_remainder,use_cooldown,enchantable,repairable,equippable,glider,tooltip_style,death_protection,item_model;food"has been changed to become a data container which only holds the food stats";fire_resistantbecamedamage_resistantwith atypesfield. - 1.21.5 (
.../minecraft-java-edition-1-21-5):weapon("When present, the "Item Used" statistic will be incremented for each attack with the item" anditem_damage_per_attack),blocks_attacks("this item can be used like a Shield"),break_sound,provides_banner_patterns,provides_trim_material,tooltip_display,potion_duration_scale;toolgainedcan_destroy_blocks_in_creative. - 1.21.11 (
.../minecraft-java-edition-1-21-11):use_effects,minimum_attack_charge,attack_range,kinetic_weapon("a charge-type attack when using the item (primarily for Spears)"),piercing_weapon. - 26.3 (
.../minecraft-java-edition-26-3):cooking_fuel,block_transformer,compostable,villager_food,mob_visibility.
Items whose components describe nothing beyond stack size and durability, so their behavior is Java code (from the 26.3 report, listing only components outside the thirteen common ones):
| Item | Components beyond the common set |
|---|---|
bucket, water_bucket, spyglass, bone_meal, lead, name_tag, snowball, compass, map, ender_eye, minecart, armor_stand, painting, item_frame, torch | none |
bow | cooking_fuel, damage, enchantable {value: 1}, max_damage 384 |
crossbow | as bow plus charged_projectiles [], max_damage 465 |
fishing_rod | cooking_fuel, damage, enchantable, max_damage 64 |
flint_and_steel, brush, carrot_on_a_stick | damage, max_damage |
ender_pearl | use_cooldown {seconds: 1.0} |
wind_charge | use_cooldown {seconds: 0.5} |
egg | chicken/variant |
splash_potion | potion_contents {} |
filled_map | map_decorations {} |
Items whose behavior components do describe them: shield (blocks_attacks with block_delay_seconds, bypassed_by, item_damage), elytra (equippable slot chest plus glider), totem_of_undying (death_protection with effects), golden_apple, honey_bottle, milk_bucket (consumable with on_consume_effects, use_remainder), chorus_fruit (teleport_randomly consume effect), copper_spear (attack_range, kinetic_weapon, piercing_weapon, damage_type: minecraft:spear), iron_shovel and iron_hoe (block_transformer), saddle and wolf_armor (equippable with allowed_entities), goat_horn (instrument), music discs (jukebox_playable). The 8 crafting_special_* recipe serializers (firework, banner duplication, shield decoration, book cloning, map extending, repair) are code behind a one-line JSON stub.
Other code
Fluids (5 entries, elements: false), potions and effects (46, 40), game events, particles, block entities (49), creative tabs (14), villager professions and types, commands and their argument types, the *_type registries that name every implementation a JSON file can reference.
4. Java worldgen as data
Everything below is in data/minecraft/worldgen/ (1144 files) plus dimension_type/ (4 files). world_preset/normal.json is the entry point:
{"dimensions": {
"minecraft:overworld": {"type": "minecraft:overworld", "generator": {"type": "minecraft:noise", "biome_source": {"type": "minecraft:multi_noise", "preset": "minecraft:overworld"}, "settings": "minecraft:overworld"}},
"minecraft:the_end": {"type": "minecraft:the_end", "generator": {"type": "minecraft:noise", "biome_source": {"type": "minecraft:the_end"}, "settings": "minecraft:end"}},
"minecraft:the_nether": {"type": "minecraft:the_nether", "generator": {"type": "minecraft:noise", "biome_source": {"type": "minecraft:multi_noise", "preset": "minecraft:nether"}, "settings": "minecraft:nether"}}}}Chunk generators: noise, flat, debug. Biome sources: fixed, multi_noise, checkerboard, the_end. 7 world presets, 9 flat presets.
noise_settings (7 files: overworld, amplified, large_biomes, caves, floating_islands, nether, end)
overworld.json top-level keys in 26.3: aquifers, debug_functions, default_block (minecraft:stone), default_fluid (minecraft:water), disable_mob_generation (false), legacy_random_source (false), material_rule ("minecraft:overworld", a reference), noise ({"height": 384, "min_y": -64}), noise_router, sea_level (63), spawn_target. 26.3 renamed and restructured this file; the changelog says "The surface_rule field has been renamed to material_rule. Format: inline Material Rule or Material Rule ID reference", "The final_density field no longer has the beardifier Density Function implicitly added to the final result", "Renamed preliminary_surface_level to chunk_surface_level. This Density Function is no longer implicitly interpolated across the entire chunk", and "The aquifers_enabled field has been replaced by an optional aquifers object: If not present, no aquifers will be generated". ore_veins_enabled is gone; ore veins are now a material_rule type (ore_vein) fed by the overworld/ore_vein/* density functions.
noise_routerhas eight entries, all references:chunk_surface_level,continents,depth,erosion,final_density,ridges,temperature,vegetation, eachminecraft:overworld/<name>.aquifershasbarrier,exclusion,fluid_level_floodedness,fluid_level_spread,lava,surface_level, each a density function (barrieris{"type": "minecraft:noise", "noise": "minecraft:aquifer_barrier", "xz_scale": 1.0, "y_scale": 0.5}).spawn_targetis a list of two parameter boxes overcontinents,erosion,ridges,temperature,vegetation(for exampleridges [-1.0, -0.16]and[0.16, 1.0]).debug_functionslabels functions for the F3 screen.- The material rule for the overworld is
worldgen/material_rule/overworld.json(388 bytes): asequencewith aconditiononabove_preliminary_surfacethat references theoverworld/subfolder. 42material_rulefiles and 8material_conditionfiles exist because 26.3 made both referenceable registries. Rule types:block,bandlands,sequence,condition,ore_vein. Condition types (11):biome,noise_threshold,vertical_gradient,y_above,water,temperature,steep,not,hole,above_preliminary_surface,stone_depth.
Density functions
55 files: overworld/ 27 (base_3d_noise, caves/{entrances,noodle,pillars,spaghetti_2d,spaghetti_2d_thickness_modulator,spaghetti_roughness_function}, chunk_surface_level, continents, depth, erosion, factor, final_density, jaggedness, offset, ore_vein/{copper_density,gap,iron_density,mask,richness,toggle}, preliminary_surface_level, ridges, ridges_folded, sloped_cheese, temperature, vegetation), overworld_amplified/ 8, overworld_large_biomes/ 12, nether/ 1, end/ 3, root 4 (shift_x, shift_z, y, zero). 64 noise/ files supply the octave definitions they reference.
The density_function_type registry has 44 operators: constant, blend_alpha, blend_offset, beardifier, noise, end_outer_islands, distance_to_point, gradient, shift_a, shift_b, shift, abs, square, cube, sqrt, half_negative, quarter_negative, reciprocal, negate, squeeze, log, sign, floor, round, ceil, truncate, add, sub, mul, div, min, max, pow, spline, lerp, clamp, range_choice, interval_select, cache, blend_density, interpolated, slice, find_top_surface, old_blended_noise. Vanilla uses 33 of them (counts across all files: add 70, noise 65, mul 64, cache 32, gradient 29, lerp 29, range_choice 21, sub 19, min 18, clamp 18, interpolated 17, abs 12, max 11, blend_alpha 9, spline 9, squeeze 7, blend_density 7, beardifier 7, quarter_negative 6, square 3, find_top_surface 3, div 3, blend_offset 3, half_negative 3, old_blended_noise 3, interval_select 3, cube 2, shift_a, shift_b, negate, slice, distance_to_point, end_outer_islands 1 each). spline carries the terrain shape as cubic splines over continents, erosion, ridges_folded; old_blended_noise is the 3D terrain noise. 26.2 added interval_select and removed weird_scaled_sampler; 1.21.9 added find_top_surface and made the surface level a 2D function.
Biomes and the multi-noise source
67 biome files. plains.json keys: attributes, carvers, downfall, effects, features, has_precipitation, temperature. carvers is ["minecraft:cave", "minecraft:cave_extra_underground", "minecraft:canyon"]; features is 11 lists, one per decoration step (plains: 0, 2, 1, 2, 0, 0, 29, 0, 2, 11, 1 placed features); effects is {"water_color": "#3f76e4"}. Mob spawns moved in 26.3 from spawners/spawn_costs to attributes["minecraft:gameplay/natural_mob_spawns"] (changelog: "Removed the spawners, spawn_costs, and creature_spawn_probability fields. These values have been moved to the new Environment Attributes"). Plains spawns, verbatim shape: {"argument": {"spawn_costs": {}, "spawns_by_category": {"ambient": [{"type": "minecraft:bat", "count": 8, "weight": 10}], "creature": [{"type": "minecraft:sheep", "count": 4, "weight": 12}, ...], "monster": [...], "underground_water_creature": [...]}}, "modifier": "overlay"}. Attribute keys used across the 67 biomes: gameplay/natural_mob_spawns 67, visual/sky_color 57, audio/background_music 43, visual/water_fog_color 9, visual/fog_color 9, gameplay/increased_fire_burnout 8, gameplay/snow_golem_melts 7, gameplay/creature_world_gen_spawn_probability 5, audio/ambient_sounds 5, visual/ambient_particles 4, and three rarer. The environment_attribute registry has 51 attributes (1.21.11: "Environment Attributes provide a data-driven way to control a variety of visual and gameplay systems").
multi_noise_biome_source_parameter_list/overworld.json is {"preset": "minecraft:overworld"}; the preset is code, and reports/biome_parameters/minecraft/overworld.json expands it to 7594 entries of the form {"biome": "minecraft:mushroom_fields", "parameters": {"continentalness": [-1.2, -1.05], "depth": 0.0, "erosion": [-1.0, 1.0], "humidity": [-1.0, 1.0], "offset": 0.0, "temperature": [-1.0, 1.0], "weirdness": [-1.0, 1.0]}}. A datapack may supply an inline biomes list in the same shape. dimension_type/overworld.json has ambient_light, attributes (11 keys), coordinate_scale, default_clock, has_ceiling, has_ender_dragon_fight, has_skylight, height, infiniburn, logical_height, min_y, monster_spawn_block_light_limit, monster_spawn_light_level, timelines.
Carvers
Registry: cave, canyon. Vanilla files: cave.json, cave_extra_underground.json, nether_cave.json (type cave), canyon.json. cave.json: probability 0.15, y, yScale, lava_level, horizontal_radius_multiplier, vertical_radius_multiplier, floor_level, thickness, weird_thickness_bias, room_vertical_radius_multiplier, count (very_biased_to_bottom 0 to 14). The parameters are data; the tunnel walk is code.
Features and placement
feature_type registry, 58 entries: bamboo, block_blob, block_column, block_pile, blue_ice, bonus_chest, chorus_plant, coral_claw, coral_tree, delta_feature, disk, end_gateway, end_island, end_platform, end_podium, end_spike, fallen_tree, fill_layer, fossil, freeze_top_layer, geode, huge_brown_mushroom, huge_fungus, huge_red_mushroom, iceberg, lake, large_dripstone, monster_room, multiface_growth, netherrack_replace_blobs, no_op, ore, overlay, projected_random_patchy_square, random_boolean_selector, random_neighbor_spread, random_selector, replace_single_block, root_system, scattered_ore, sculk_patch, sequence, simple_block, simple_random_selector, single_block_pillar, speleothem, speleothem_cluster, spike, spring_feature, stepped_column_cluster, template, tree, underwater_magma, vegetation_patch, vines, void_start_platform, waterlogged_vegetation_patch, weighted_random_selector. The 240 vanilla feature/ files use 47 of them (tree 45, simple_block 37, ore 30, random_selector 21, overlay 10, weighted_random_selector 8, ...). Trees compose 10 trunk placers, 12 foliage placers, 11 tree decorators, 1 root placer and 2 feature sizes; block choice uses 10 block_state_provider types; ore targets use 10 rule_test types.
placement_modifier_type registry, 18 entries: block_predicate_filter, rarity_filter, random_chance, surface_relative_threshold_filter, surface_water_depth_filter, biome, count, noise_based_count, noise_threshold_count, count_on_every_layer, cuboid, environment_scan, heightmap, height_range, in_square, offset, randomly_selected, fixed_placement. The 273 placed_feature/ files use 15 (biome 211, count 201, in_square 198, block_predicate_filter 155, heightmap 111, offset 93, height_range 86, rarity_filter 55, surface_water_depth_filter 26, environment_scan 12, count_on_every_layer 8, noise_threshold_count 6, noise_based_count 4, surface_relative_threshold_filter 3, fixed_placement 1), with 16 block_predicate_types, 6 height providers, 8 int providers and 4 float providers. placed_feature/ore_diamond.json, verbatim:
{"feature": "minecraft:ore_diamond_small", "placement": [
{"type": "minecraft:count", "count": 7}, {"type": "minecraft:in_square"},
{"type": "minecraft:height_range", "height": {"type": "minecraft:trapezoid", "max_inclusive": {"above_bottom": 80}, "min_inclusive": {"above_bottom": -80}}},
{"type": "minecraft:biome"}]}Structures
structure_type registry, 16 entries: buried_treasure, desert_pyramid, end_city, fortress, igloo, jigsaw, jungle_temple, mineshaft, nether_fossil, ocean_monument, ocean_ruin, ruined_portal, shipwreck, stronghold, swamp_hut, woodland_mansion. The 52 structure/ files: jigsaw 28 (villages, bastions, pillager outposts, ancient city, trail ruins, trial chambers, abandoned camp), ruined_portal 7, mineshaft 2, ocean_ruin 2, shipwreck 2, one each of the rest. village_plains.json: {"type": "minecraft:jigsaw", "biomes": "#minecraft:has_structure/village_plains", "max_distance_from_center": 80, "project_start_to_heightmap": "WORLD_SURFACE_WG", "size": 6, "spawn_overrides": {}, "start_height": {"absolute": 0}, "start_pool": "minecraft:village/plains/town_centers", "step": "surface_structures", "terrain_adaptation": "beard_thin", "use_expansion_hack": true}. The 15 non-jigsaw types are code with a biome tag and a few fields each; worldgen/structure_piece has 56 code-defined piece types.
21 structure_set/ files; structure_placement types concentric_rings (strongholds), dimension_origin, random_spread (the other 20). villages.json: {"placement": {"type": "minecraft:random_spread", "salt": 10387312, "separation": 8, "spacing": 34}, "structures": [{"structure": "minecraft:village_plains", "weight": 1}, ...]}.
245 template_pool/ files with 2281 elements: legacy_single_pool_element 1663, single_pool_element 527, feature_pool_element 57, empty_pool_element 31, list_pool_element 3. 40 processor_list/ files using 4 of the 11 structure_processor types (rule 35, protected_blocks 7, block_rot 6, capped 4; unused: blackstone_replace, block_age, block_ignore, gravity, jigsaw_replacement, lava_submerged_block, nop), with 10 rule_test, 3 pos_rule_test and 4 rule_block_entity_modifier types. 3 pool_alias_binding types.
What a server must implement to run this
The noise chunk generator (cell interpolation, the noise_router contract, aquifers, the material rule evaluator, beardifier and blend_* against structures and legacy chunks), the 44 density function operators including splines and old_blended_noise, the multi-noise lookup, the two carver algorithms, the 58 feature algorithms with their placers and decorators, the 18 placement modifiers, 16 structure algorithms plus jigsaw assembly with 5 element types and 11 processors, 3 structure placement algorithms, and the height, int, float, block-state-provider and block-predicate providers. Vanilla exercises 33 density operators, 47 features, 15 modifiers, 2 carvers, 16 structure types, 4 processors. Mojang publishes no specification of any of these beyond the JSON schema implied by the files and the changelog prose; the reference is the decompiled client.
5. Licensing of the Java data
Not legal advice. Texts as published.
EULA (https://www.minecraft.net/en-us/eula): "When you buy our games, that means you can download, install, and play them. For the server version of Minecraft: Java Edition, you can install it on a server and host online play. However, you must not distribute anything we've made unless we specifically agree to it. By "distribute anything we've made" what we mean is: give copies of our game software or content to anyone else; make commercial use of anything we've made; ..." and "In order to ensure the integrity of our games, we need all game downloads and updates to come from a source that we authorize." The Bedrock note already quotes the "USING mods" section and the Usage Guidelines; the same texts govern the Java jar and its generated output.
misode/mcmeta (https://github.com/misode/mcmeta): no LICENSE file on master, summary or data (raw fetch returns 404). README "Disclaimer", verbatim: "mcmeta is not an official Minecraft product, and is not endorsed by or associated with Mojang Studios. All data and assets were obtained through Mojang's internal data generator and public API. If Mojang ever has something against this data existing here, the repository will be promptly removed."
PrismarineJS/minecraft-data (https://github.com/PrismarineJS/minecraft-data, master = 5e063fa99cfe8ded065ec6788b66696b7e4ef143): README section "License", verbatim: "MIT. Some of the data was extracted manually or automatically from wiki.vg and minecraft.gamepedia.com. If required by one of the sources the license might change to something more appropriate." No LICENSE, LICENSE.md, LICENCE or LICENSE.txt exists at that commit's root (all 404 on raw.githubusercontent.com). Its README credits "burger with burger-extractor ... minecraft server jar ... used to provide items, blocks, biomes and recipes", the "Minecraft data generator" for commands, and "minecraft-data-generator ... minecraft client" (a Fabric mod) for "biomes, block collision shapes, blocks, effects, enchantments, entities, foods, items, particles, tints". The CC0 republishers named in the Bedrock note (pmmp/BedrockData, AllayMC/BedrockData) are Bedrock projects; minecraft-data is MIT by its own statement.
6. Fit for a Bedrock server
Bedrock column from bedrock-data-extraction.md sections 2 to 4 (BDS 1.26.51.1, bedrock-samples v1.26.50.4).
| Category | Java datapack (26.3) | Bedrock behavior pack (1.26.51) | Richer |
|---|---|---|---|
| Blocks | none; 1286 blocks are code, properties never reported | 98 of 1463 as JSON with mining time, resistance, map color, loot, archetype; the rest code | Bedrock, slightly |
| Block states | reports/blocks.json: names, values, ids for 35723 states (generated, read-only) | mojang-blocks.json names and global domains; per-block domains only from a saved world | Java (complete per-block domains) |
| Items | 1658 default-component files, 122 component types, behavior for food, tools, armor, weapons, shields, elytra, totems, spears | 74 items as JSON (foods, bundles, spears, seeds); 46 documented components; tools, armor, bows, shields, buckets, elytra are code | Java |
| Entities | none; 161 types, attributes, brains, sensors are code; variants and spawn lists are data | 130 entities as JSON: 379 component keys, 174 behavior.* goals, component groups, events | Bedrock |
| Loot | 1447 tables, 9 entry types, 42 modifiers, 20 conditions, predicates and item modifiers as files; block loot for all 1201 drop-bearing blocks | 309 tables; block loot only for the 98 data-driven blocks | Java |
| Recipes | 2042, 22 serializers, brewing as data since 26.3 | 1892, 6 types including recipe_brewing_mix | Java |
| Tags | 883 files over 16 registries, referenced by tools, loot, worldgen, trades | tags inside entity, item and block files plus query.any_tag in Molang; no tag files | Java |
| Biomes | 67 files: climate, effects, carvers, 11 feature steps, spawns, attributes | 89 files: climate, surface builder, tags, nether multinoise weights; overworld placement components marked unused | Java |
| Terrain | noise settings, density functions, splines, aquifers, material rules, multi-noise parameters | engine code, no parameters ("The terrain generation pass doesn't offer much customization") | Java |
| Carvers | 4 configured carvers over 2 types | 3 carver feature definitions under definitions/features/, algorithm engine | Java |
| Features | 240 configured + 273 placed over 58 types and 18 modifiers | 210 features + 241 feature rules over 25 types, Molang distributions | Java (more types, modifiers as a stack); Bedrock has Molang |
| Structures | 52 structures over 16 types, 21 sets, 245 pools, 40 processor lists, 1511 NBT | 1311 NBT pieces, jigsaw JSON for trail ruins and abandoned camps only; other assembly engine | Java |
| Spawning | per-biome weights, counts, costs under natural_mob_spawns; caps and light rules in code and dimension_type | 60 spawn rules with brightness, difficulty, herds, biome filters; pool caps engine | Bedrock (per-mob conditions), Java (per-biome lists) |
| Trading | 391 trades, 68 trade sets, tags, since 26.1 | 27 trade tables | Java |
| Enchantments | 43 with cost curves and 31 effect component types | 42 names in mojang-enchantments.json, no definitions ("Max enchantment levels are hard-coded") | Java |
| Damage types | 51 files with scaling and exhaustion, tags | none as files (damage causes are enum values in entity JSON) | Java |
| Advancements | 1866 with 58 triggers | none (achievements are code) | Java |
Identifier differences
Checked Java's minecraft:block and minecraft:item registries against this repository's Bedrock captures: packages/minecraft/datagen/snapshot/v2193/block-palette.json (states, 1477 block names from BDS 1.26.51.1) and packages/bedrock-data/src/jsp/required_item_list.json (2076 item names from ItemRegistryPacket). A third file read at the time, block_id_map.json (553 pre-flattening names such as minecraft:wool, minecraft:concrete, minecraft:stonebrick), was the legacy table and was never usable for name matching; it has since been deleted as unreferenced.
Blocks: 1102 of 1286 Java names exist in the Bedrock palette; 184 are Java-only and 375 Bedrock-only. The Java-only names are one block in Java where Bedrock has none or has several: 16 *_bed (Bedrock bed), 32 *_banner and *_wall_banner (Bedrock standing_banner, wall_banner), 39 potted_* (Bedrock flower_pot with a block entity), 13 *_sign and 13 *_wall_hanging_sign (Bedrock *_standing_sign), oak_wall_sign and dark_oak_wall_sign (Bedrock wall_sign, darkoak_wall_sign), 7 *_wall_head and *_wall_skull, wall_torch, redstone_wall_torch, soul_wall_torch, comparator, repeater, piston_head, moving_piston, cave_air, void_air, water_cauldron, lava_cauldron, powder_snow_cauldron, kelp_plant, cave_vines_plant, twisting_vines_plant, weeping_vines_plant, tall_seagrass, plus renamed singles. Bedrock-only names are 93 *_double_slab, 120 element_*, 16 light_block_*, 34 hard_*glass*, 13 *standing_sign, lit_furnace, lit_blast_furnace, lit_smoker, lit_redstone_ore, lit_deepslate_redstone_ore, lit_redstone_lamp, lit_pumpkin, unlit_redstone_torch, powered_repeater, unpowered_repeater, powered_comparator, unpowered_comparator, flowing_water, flowing_lava, daylight_detector_inverted, piston_arm_collision, sticky_piston_arm_collision, moving_block, invisible_bedrock, allow, deny, border_block, camera, chalkboard, portal, info_update, reserved6, unknown, and the education chemistry blocks.
Renames between the two, found in that pass: Java cobweb / Bedrock web; dead_bush / deadbush; dirt_path / grass_path; lily_pad / waterlily; magma_block / magma; slime_block / slime; spawner / mob_spawner; note_block / noteblock; melon / melon_block; bricks / brick_block; nether_bricks / nether_brick; red_nether_bricks / red_nether_brick; end_stone_bricks / end_bricks; end_stone_brick_stairs / end_brick_stairs; prismarine_brick_stairs / prismarine_bricks_stairs; nether_quartz_ore / quartz_ore; nether_portal / portal; powered_rail / golden_rail; sugar_cane / reeds; snow_block / snow and snow / snow_layer; stone_slab / normal_stone_slab; cobblestone_stairs / stone_stairs; jack_o_lantern / lit_pumpkin; terracotta / hardened_clay; light_gray_glazed_terracotta / silver_glazed_terracotta; rooted_dirt / dirt_with_roots; small_dripleaf / small_dripleaf_block; frogspawn / frog_spawn; flowering_azalea_leaves / azalea_leaves_flowered; shulker_box / undyed_shulker_box; waxed_copper_block / waxed_copper; tripwire / trip_wire; oak_door / wooden_door; oak_trapdoor / trapdoor; oak_fence_gate / fence_gate; oak_button / wooden_button; oak_pressure_plate / wooden_pressure_plate; beetroots / beetroot; light / light_block_<n>; oak_sign + oak_wall_sign / standing_sign + wall_sign; dark_oak_* signs / darkoak_*. Names that match on both sides include grass_block, short_grass, tall_grass, oak_log, oak_stairs, oak_slab, white_wool, white_concrete, white_carpet, oak_leaves, oak_fence, stone_bricks, cobblestone_wall, red_sandstone_wall, dandelion, poppy, wheat, carrots, potatoes, furnace, redstone_torch, water, smooth_stone_slab, cave_vines (Bedrock adds cave_vines_body_with_berries and cave_vines_head_with_berries). State axes differ even where names match: Java oak_log has axis, oak_stairs has facing, half, shape, waterlogged, and oak_slab has type, waterlogged; in the Bedrock palette oak_log has pillar_axis, oak_stairs has minecraft:corner, upside_down_bit, weirdo_direction, and oak_slab has minecraft:vertical_half. No Bedrock block in the palette has a waterlogged state (water is a separate layer). So a shared identifier does not give a shared state space, and the double-slab, lit, powered and flowing families mean one Java block often maps to two Bedrock blocks.
Items: 1565 of 1658 Java item names exist in the Bedrock table. The 93 Java-only are the 16 *_bed and 16 *_banner items (Bedrock bed, banner), map and 16 *_map explorer maps (Bedrock uses empty_map and filled_map with data), block items named differently (bricks, cobweb, dirt_path, lily_pad, magma_block, melon, nether_bricks, note_block, oak_door, powered_rail, slime_block, snow_block, spawner, stone_slab, terracotta, waxed_copper_block), spectral_arrow, tipped_arrow (Bedrock arrow with data), knowledge_book, debug_stick, glow_item_frame and item_frame (Bedrock frame, glow_frame), furnace_minecart, zombified_piglin_spawn_egg (Bedrock zombie_pigman_spawn_egg), test_block, test_instance_block. The 511 Bedrock-only are 120 element_*, 93 *_double_slab, 24 sign block items, 18 item.* aliases, 16 *_candle_cake, 16 light_block_*, 10 *coral_wall_fan, education items (balloon, bleach, compound, ice_bomb, glow_stick), legacy flattened names (banner, bed, boat, carpet, concrete, concrete_powder, coral, coral_block, coral_fan, dye, fence, double_plant, empty_map), and technical blocks exposed as items (bubble_column, fire, flowing_water, end_gateway, end_portal, frosted_ice).
What this means for the format question
Java datapacks are a complete, Mojang-maintained, generator-verifiable description of vanilla terrain, decoration, structures, loot, recipes, tags, enchantments, trades and item components, and the only one of the two editions with any of the first three in data. They say nothing about blocks (the one place where Bedrock's 98 files and block_archetype say a little more) and nothing about entities (where Bedrock's 130 files say almost everything). A server that wants vanilla Bedrock parity from data would take entities, spawn rules and the block archetype idea from Bedrock's format, and could take loot, recipe, tag, enchantment and worldgen structure from Java's, with a name and state mapping between the two palettes for every block reference inside worldgen and loot files. The mapping has 184 plus 375 exceptions on the block side and differing state axes on all stairs, logs, slabs and waterloggable blocks, so it is a table the project must own, not a rename rule. Loading Java files unmodified at runtime would also import 26.3-specific renames (material_rule, modifier, condition, natural_mob_spawns) that change every few releases; the Java changelogs show one breaking datapack rename per release through 1.21.9, 1.21.11, 26.1, 26.2 and 26.3.
Open questions
- Why 26.3 removed
definitionfromblocks.jsonand whether anything will replace it is not stated in the changelog beyond the one sentence quoted. 26.2's dump is the last public list of Java block classes. - Bedrock's
mojang-blocks.jsonwas not re-read here; the per-block state axis comparison relies on the Bedrock note's examples and should be run over all 1102 shared names before any mapping table is built. - Java's multi-noise preset (
minecraft:overworld) is code; the 7594-point expansion inreports/biome_parameters/is complete for lookup, but the spline and parameter semantics (for example theoffsetfield) are not documented anywhere by Mojang. - The
--devflag produced no additional files in 26.3; whether--validateor--inputcan be used to run Mojang's own validation on a third-party pack was not tried. - Whether misode/mcmeta's
databranch is byte-identical to the generator output for 26.3 was not diffed; its README claims it is the generator output. - The GitHub REST API rate-limited unauthenticated requests during this pass; branch heads were taken from
git ls-remoteinstead, which is equally authoritative.
Reproduction
# Where the current Java server jar is
curl -sS https://net-secondary.web.minecraft-services.net/api/v1.0/download/links | python3 -I -m json.tool
curl -sS https://piston-meta.mojang.com/mc/game/version_manifest_v2.json -o version_manifest_v2.json
curl -sS https://piston-meta.mojang.com/v1/packages/61fff1316bd50312624a858bbb5eb18fa45208ed/26.3.json -o 26.3.json
# Download into an empty directory and verify
mkdir -p /tmp/bds-research-java/jar /tmp/bds-research-java/out /tmp/bds-research-java/tools
cd /tmp/bds-research-java/jar
curl -sS -L -o server.jar https://piston-data.mojang.com/v1/objects/33680f5f2ac32864d6d7cf5e56a705fdb3e05f4c/server.jar
shasum -a 1 server.jar # 33680f5f2ac32864d6d7cf5e56a705fdb3e05f4c
shasum -a 256 server.jar # d052f14d7a173734fba553711e5b570162e2f2a313267ee31a21b975a679be64
unzip -p server.jar version.json
# Run the data generator (needs Java 25; macOS: /usr/libexec/java_home -V)
JAVA=/Library/Java/JavaVirtualMachines/graalvm-25.jdk/Contents/Home/bin/java
cd /tmp/bds-research-java/out
$JAVA -DbundlerMainClass=net.minecraft.data.Main -jar /tmp/bds-research-java/jar/server.jar --help
$JAVA -DbundlerMainClass=net.minecraft.data.Main -jar /tmp/bds-research-java/jar/server.jar \
--reports --server --all --output /tmp/bds-research-java/out/generated
# Counts used above
cd /tmp/bds-research-java/out/generated
for d in data/minecraft/*/ data/minecraft/worldgen/*/ data/minecraft/tags/*/; do printf "%s\t%s\n" "$(find "$d" -type f | wc -l)" "$d"; done
ls reports; ls reports/minecraft/components/item | wc -l
python3 -I -c 'import json;b=json.load(open("reports/blocks.json"));print(len(b),sum(len(v["states"]) for v in b.values()));print(json.dumps(b["minecraft:stone"]))'
python3 -I -c 'import json;r=json.load(open("reports/registries.json"));[print(len(v["entries"]),k) for k,v in sorted(r.items())]'
python3 -I -c 'import json;d=json.load(open("reports/datapack.json"));print(sum(v["elements"] for v in d["registries"].values()),len(d["registries"]))'
cat reports/minecraft/components/item/diamond_pickaxe.json reports/minecraft/components/item/apple.json
unzip -l /tmp/bds-research-java/out/versions/26.3/server-26.3.jar | grep -c 'data/minecraft/structure/.*\.nbt$'
unzip -p /tmp/bds-research-java/out/versions/26.3/server-26.3.jar data/minecraft/datapacks/trade_rebalance/pack.mcmeta
# Dating the removal of blocks.json "definition": same command with the 1.21.11, 26.1 and 26.2 jars
# (sha1 64bb6d763bed0a9f1d632ec347938594144943ed, 3872a7f07a1a595e651aef8b058dfc2bb3772f46, 823e2250d24b3ddac457a60c92a6a941943fcd6a)
# each in its own /tmp/bds-research-java/jar-<v>/ and /tmp/bds-research-java/out-<v>/, with --reports only.
# Republishers
git ls-remote https://github.com/misode/mcmeta refs/heads/summary refs/heads/data refs/heads/registries
git ls-remote --tags https://github.com/misode/mcmeta | grep 'refs/tags/26.3-'
curl -sS -L https://raw.githubusercontent.com/misode/mcmeta/master/README.md
curl -sS -L https://raw.githubusercontent.com/PrismarineJS/minecraft-data/master/README.md | sed -n '/## License/,/## Related/p'
# Changelogs (served as HTML; strip tags and grep)
for a in minecraft-snapshot-24w09a minecraft-java-edition-1-20-5 minecraft-java-edition-1-21-2 minecraft-java-edition-1-21-5 \
minecraft-java-edition-1-21-9 minecraft-java-edition-1-21-11 minecraft-java-edition-26-1 minecraft-java-edition-26-2 minecraft-java-edition-26-3; do
curl -sS -L -A "Mozilla/5.0" -o "$a.html" "https://www.minecraft.net/en-us/article/$a"; done
# Identifier comparison against this repository's Bedrock captures
# packages/minecraft/datagen/snapshot/v2193/block-palette.json ("states" keys) and packages/bedrock-data/src/jsp/required_item_list.json (keys)
# versus reports/registries.json "minecraft:block" and "minecraft:item" entries.