Library of Leng — ruling 1

If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then put Library of Leng onto the battlefield, you'll have no maximum hand size. However, if those permanents entered in the opposite order, your maximum hand size would be two.

Library of Leng — ruling 2

You can't use the Library of Leng ability to place a discarded card on top of your library when you discard a card as a cost, because costs aren't effects.

Library of Leng — ruling 3

The discard triggers anything else that triggers on discards.

Library of Leng — ruling 4

You can look at a randomly discarded card before deciding where it goes.

Library of Leng — ruling 5

This effect has no effect on the cards being put into the graveyard from a library, because they are not "discarded".

Library of Leng — ruling 6

If more than one card is discarded due to a single effect, the Library allows you to decide whether or not to use it on each of the cards. You get to decide the order the cards are placed on the library if more than one goes there.

Library of Leng — ruling 7

Since the card goes directly to the library, the card is not revealed unless the spell or ability requiring the discard specifically says it is.

Library of Leng — ruling 8

The ability replaces the normal discard action with a discard action that puts the card on the library instead of the graveyard.

Library of Leng : règles, fonctionnement et interactions (MTG)

Library of Leng is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

You have no maximum hand size. If an effect causes you to discard a card, discard it, but you may put it on top of your library instead of into your graveyard.

Complete guide

Library of Leng is a classic utility artifact that offers both hand-size freedom and a unique way to protect your resources. By allowing you to bypass the graveyard when discarding to effects, it keeps your most valuable cards within reach.

Endless Possibilities

The first ability of Library of Leng is straightforward: you have no maximum hand size. This means during your cleanup step, you do not have to discard down to seven cards. Note that if other cards like Null Profusion are in play, you must apply their effects in timestamp order to determine your actual hand size.

How the Replacement Effect Resolves

The second ability is a replacement effect that applies when an effect, such as a spell or ability, causes you to discard. Instead of the card going to the graveyard, you may choose to put it on top of your library. This happens as part of the discard action itself, meaning the card never actually touches the graveyard. If multiple cards are discarded at once, you choose whether to apply this to each card individually and determine their order on top of your library.

Costs vs. Effects

The most common mistake with Library of Leng is trying to use it while paying a cost. If a card says 'Discard a card: [Effect],' the discard is a cost, and the Library cannot save that card. It only works when a spell or ability’s resolution forces a discard, such as an opponent's discard spell or your own draw-and-discard effect.

Strategic Timing

Play Library of Leng early to establish hand-size immunity. It is particularly effective in decks that use 'looting' effects (drawing then discarding) to filter through the deck, as it allows you to 'redraw' the same powerful card next turn instead of losing it to the graveyard.

Interaction examples

Basic Utility with Mana Rocks

Sol Ring

Arcane Signet

Step 1: You cast Sol Ring and Arcane Signet to accelerate your mana production. Step 2: You cast Library of Leng. From this point forward, you no longer need to worry about discarding during your cleanup step, regardless of how many cards you draw with your excess mana. If an opponent casts a spell that forces you to discard, you can use the Library to put your best card back on top of your deck.

Handling Random Discard

If an effect forces you to discard a card at random, you first determine which card is being discarded. Once the card is chosen, you are allowed to look at it. You then decide whether to let it go to the graveyard or use Library of Leng to place it on top of your library. This ensures that even random effects cannot permanently strip away your win conditions.

Guide written with AI from the official text and rulings. Official English text prevails.

How it works : Library of Leng

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
If multiple effects modify your hand size, apply them in timestamp order. For example, if you put Null Profusion (an enchantment that says your maximum hand size is two) onto the battlefield and then put Library of Leng onto the battlefield, you'll have no maximum hand size. However, if those permanents entered in the opposite order, your maximum hand size would be two.
No other card is named in this ruling.
#2October 4, 2004· Wizards of the Coast
You can't use the Library of Leng ability to place a discarded card on top of your library when you discard a card as a cost, because costs aren't effects.
No other card is named in this ruling.
#3October 4, 2004· Wizards of the Coast
The discard triggers anything else that triggers on discards.
No other card is named in this ruling.
#4October 4, 2004· Wizards of the Coast
You can look at a randomly discarded card before deciding where it goes.
No other card is named in this ruling.
#5October 4, 2004· Wizards of the Coast
This effect has no effect on the cards being put into the graveyard from a library, because they are not "discarded".
No other card is named in this ruling.
#6October 4, 2004· Wizards of the Coast
If more than one card is discarded due to a single effect, the Library allows you to decide whether or not to use it on each of the cards. You get to decide the order the cards are placed on the library if more than one goes there.
No other card is named in this ruling.
#7October 4, 2004· Wizards of the Coast
Since the card goes directly to the library, the card is not revealed unless the spell or ability requiring the discard specifically says it is.
No other card is named in this ruling.
#8October 4, 2004· Wizards of the Coast
The ability replaces the normal discard action with a discard action that puts the card on the library instead of the graveyard.
No other card is named in this ruling.
#9October 4, 2004· Wizards of the Coast
The ability applies any time a spell or ability has you discard as part of its effect. It does not matter if you or your opponent control the spell or ability. The discard is forced because it is an effect.
No other card is named in this ruling.