It's a series of JSON files.

advancements/chest_recipe.json

{ "rewards": { "recipes": ["minecraft:chest"] }, "criteria": { "slightly_full_inventory": { "trigger": "minecraft:inventory_changed", "conditions": { "slots": { "occupied": 9 } } }, "already_has_recipe": { "trigger": "minecraft:recipe_unlocked", "conditions": { "recipe": "minecraft:chest" } } }, "requirements": [["slightly_full_inventory"], ["already_has_recipe"]] } 

advancements/upgrade_tools.json

{ "display": { "icon": "minecraft:stone_pickaxe", "title": "Upgrade tools" }, "parent": "minecraft:story/mine_stone", "criteria": { "stone_pickaxe": { "trigger": "minecraft:inventory_changed", "conditions": { "items": [ { "item": "minecraft:stone_pickaxe" } ] } } } } 

recipes/book.json

{ "type": "crafting_shapeless", "ingredients": [ { "item": "minecraft:paper" }, { "item": "minecraft:paper" }, { "item": "minecraft:paper" }, { "item": "minecraft:leather" } ], "result": { "item": "minecraft:book" } } 

recipes/golden_axe.json

{ "type": "crafting_shaped", "pattern": [ "XX", "X#", " #" ], "key": { "#": { "item": "minecraft:stick" }, "X": { "item": "minecraft:gold_ingot" } }, "result": { "item": "minecraft:golden_axe" } }