[RPG] How to calculate the chance of failure when copying spells in Adventurers League


In a recent D&D 5e Adventurers League adventure, two of our characters attempted to copy spells from each-other's spellbooks. The DM told us that each character would need to roll an Arcana check to determine success or failure in the copying of the spell.

Rules on copying spells can be found in the Player's Handbook on page 114 as well as in the most recent Adventurer's League Player's Guide (Version 6.0, effective March 24, 2017) on page 5. Here is the link.

In the AL Guide, it stipulates (emphasis mine):

Downtime: Copying Spells

If you wish to copy spells into your spellbook, you must do so using
this downtime activity—even if it occurs during an adventure.

For each downtime day spent copying spells, a character may spend
eight hours copying spells into their spellbook. Two or more
characters participating in the same adventure together at the same
table that choose to perform this downtime activity may allow one
another access to their spellbook; effectively “trading” spells
between everyone involved to copy as normal. Both parties to the trade
must perform this downtime activity to trade spells.

As there may sometimes be a chance of failure when copying spells, you must perform this downtime activity in the presence of the table’s

Here are my questions:

  1. As the text says there "may sometimes be" a chance of failure, can the DM ultimately decide if a roll is required or not, or is there a written rule somewhere that requires it?

  2. Are there any written rules on how this chance of failure is to be calculated?

Best Answer

You always succeed if your source is a spellbook. None of the rules about that contain anything about an ability check or a chance to fail. Failure matters only when you use a scroll, as it will be lost regardless of the success of your attempt.

A wizard spell on a spell scroll can be copied just as spells in spellbooks can be copied. When a spell is copied from a spell scroll, the copier must succeed on an Intelligence (Arcana) check with a DC equal to 10 + the spell's level. [...] Whether the check succeeds or fails, the spell scroll is destroyed. (DMG 200)