【Rails】Scaffoldで生成したcontrollerにあるjsonって何？

class DiariesController < ApplicationController
  before_action :set_diary, only: %i[ show edit update destroy ]

  省略

  def create
    @diary = Diary.new(diary_params)

    respond_to do |format|
      if @diary.save
        format.html { redirect_to @diary, notice: "Diary was successfully created." }
        format.json { render :show, status: :created, location: @diary }
      else
        format.html { render :new, status: :unprocessable_entity }
        format.json { render json: @diary.errors, status: :unprocessable_entity }
      end
    end
  end

  省略

end

format.json { render :show, status: :created, location: @diary }

json.partial! "diaries/diary", diary: @diary

json.extract! diary, :id, :title, :body, :created_at, :updated_at
json.url diary_url(diary, format: :json)