Intermediate Gameplay FAQ: Introduction to Speed Spells

Spell Speed refers to how "fast" card effect resolves after activation. There are 3 Spell Speeds:
Spell Speed 1
Spell Speed 1 is the slowest of all Spell Speeds. These card effects cannot be chained in response to any other Spell Speed effects. Typically, these effects cannot be Chain Link 2 or higher, unless multiple Spell Speed 1 effects are activated simultaneously.

The following are all Spell Speed 1:

-Normal/Field/Continuous/Equip & Ritual Spell Cards
-Flip/Ignition and Trigger Effects
-Ignition-like & Trigger-like Effects

Rules
Non-Quick-Play Spell Cards, Ignition Effects and Ignition-like Effects can only be used if the game state is open in your Main Phase, unless stated on the card itself (such as "Curse of Fiend").

Spell Speed 1 effects cannot be chained in response to any other effects e.g. When you activate "Storm"; you cannot then activate "Pot of Greed" in response to draw cards before using "Storm" effect, since "Pot of Greed" is a Normal Spell Card, and is therefore Spell Speed 1.

The only case in which Spell Speed 1 effects can be chained against each other, is when they activate simultaneously e.g. 2 "Mystic Tomatos" attacking each other, or 2 "Sangans" attacking each other, with each effect activating in the Graveyard.

Spell Speed 2
Spell Speed 2 card effects can be used in response to Spell Speed 1 and other Spell Speed 2 effects, but cannot used in response to Spell Speed 3 effects. Spell Speed 2 effects are also called "Fast Effects".
The following are all Spell Speed 2:

-Quick-Play Spell Cards
-Normal & Continuous Trap Cards
-Quick Effects
-Quick-like Effect

Spell Speed 3
Spell Speed 3 card effects can be used in response to Spell Speed 1, Spell Speed 2, and other Spell Speed 3 effects. Spell Speed 3 effects can only be countered with other Spell Speed 3 effects. Spell Speed 3 effects are also called "Fast Effects".

The only cards that have Spell Speed 3 effects are Counter Trap Cards.

Each Spell Speed can only be countered with one that is greater, or equal. The exception to this is Spell Speed 1, which cannot be used against each other in normal play, unless special situations allow it. See "Simultaneous Effects Go On Chain" for more explanation on this.

Summoning a monster and declaring an attack are actions that do not have a Spell Speed, and therefore cannot be "chained" to. However, if the action in question was the last action to have resolved on the field, you may activate a card in response, which then becomes Chain Link 1. For example, using "Bottomless Trap Hole" when a monster is Summoned, or using "Mirror Force" when your opponent's monster declares an attack, and all considered to be "activated in response".