Replace § colors in the display tags with the normal json color format (§c -> "color":"red"). (Or vice versa, to reduce the weight of the item)
Remove unnecessary tags like "underlined":"false" from some items that were created using some plugins via /setname /setlore
Fix broken display in items like this: Name:'{"text":"{\\"extra\\":[{\\"bold\\":true,\\"color\\":\\"dark_green\\",\\"text\\":\\"Broken \\"},{\\"bold\\":true,\\"color\\":\\"dark_green\\",\\"text\\":\\"Name\\"}],\\"text\\":\\"\\"}"}'
(remove \\, delete {"text":" at the start and "} at the end)
Replace "text":"\\u0442\\u0435\\u0441\\u0442" to "text":"тест" in books that generated with https://minecraft.tools/book.php (unicode characters formatting issue)
The NBT Beautifier functions:
Name:'{"text":"{\\"extra\\":[{\\"bold\\":true,\\"color\\":\\"dark_green\\",\\"text\\":\\"Broken \\"},{\\"bold\\":true,\\"color\\":\\"dark_green\\",\\"text\\":\\"Name\\"}],\\"text\\":\\"\\"}"}'(remove\\, delete{"text":"at the start and"}at the end)"text":"\\u0442\\u0435\\u0441\\u0442"to"text":"тест"in books that generated with https://minecraft.tools/book.php (unicode characters formatting issue)