Sigarda, Font of Blessings — ruling 1

Sigarda lets you look at the top card of your library whenever you want (with one restriction—see below), even if you don't have priority. This action doesn't use the stack. Knowing what that card is becomes part of the information you have access to, just like you can look at the cards in your hand.

Sigarda, Font of Blessings — ruling 2

If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so. This means that if you cast the top card of your library, you can't look at the next one until you're done paying for that spell.

Sigarda, Font of Blessings : règles, fonctionnement et interactions (MTG)

Sigarda, Font of Blessings 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

Flying Other permanents you control have hexproof. You may look at the top card of your library any time. You may cast Angel spells and Human spells from the top of your library.

How it works : Sigarda, Font of Blessings

Original English text — Wizards of the Coast / Scryfall

#1May 12, 2023· Wizards of the Coast
Sigarda lets you look at the top card of your library whenever you want (with one restriction—see below), even if you don't have priority. This action doesn't use the stack. Knowing what that card is becomes part of the information you have access to, just like you can look at the cards in your hand.
No other card is named in this ruling.
#2May 12, 2023· Wizards of the Coast
If the top card of your library changes while you're casting a spell, playing a land, or activating an ability, you can't look at the new top card until you finish doing so. This means that if you cast the top card of your library, you can't look at the next one until you're done paying for that spell.
No other card is named in this ruling.