Ritual Converter (5e Feat)
From D&D Wiki
Prerequisites: Ability to cast spells, ritual casting and a book
After long and extensive studies of spells, you have learned to use them as rituals, which take longer to cast than usual.
You can add the ritual tag onto a 1st level or higher spell in your book, of any kind, and you can cast these spells as rituals. For each level of the spell, the process to add the ritual tag takes 10 days and cost 200 gp, which can be accomplished while traveling as well as during downtime. This cost represents the material components you expend as you experiment with the spell to master it as a ritual, as well as the fine inks you need to record it. You do not need to have these spells in this book prepared to use them as a ritual and they do not count against the number of spells you know.
On your adventures, if you come across a 1st level or higher spell that does not have a ritual tag on it in written from, such as a magical scroll or a wizard's spellbook, you can add it to your book if the spell is not higher than half your level (rounded up) and you have the time to transcribe the spell. For each level of the spell, the transcription process takes 2 hours and costs 50 gp for the rare inks needed to transcribe it. You can't cast the spells that you have transcribed this way except as rituals, unless you've learned them by some other means.