Chain Timing And Activation Windows

Chain timing is the part of a script that decides when an activated effect can be offered to a player, when it can respond to another Chain Link, and which checks still have to pass before the activation is legal.

The most important beginner habit is to separate the prompt from the legality. SetHintTiming can help the client ask at useful moments, but it does not make the effect legal by itself. The real permission still comes from the effect type, event code, range, condition, cost, and target check.

Three Layers

Read activated timing in layers:

Layer	Script pieces	Job
Broad window	SetType, SetCode, SetRange, SetProperty	Describes the kind of activation and the event or open window it belongs to.
Prompt timing	SetHintTiming, TIMING_*, TIMINGS_CHECK_MONSTER	Helps the client decide when to offer or highlight optional effects.
Legality	condition, cost, target, chk==0	Decides whether this activation is actually allowed right now.

A script usually needs all three. A good prompt with no legal target still should not activate. A legal Quick Effect with no useful hint timing may still exist, but it may be less comfortable for the player to find at the right window.

Free Chain Windows

Many Spell/Trap activations use EVENT_FREE_CHAIN. This means the effect is not waiting for a specific event such as a monster being destroyed. It can be offered in open response windows if its type, card type, range, and legality checks allow it.

Book of Moon (c14087893.lua) is the clean local pattern:

local e1=Effect.CreateEffect(c)
e1:SetCategory(CATEGORY_POSITION+CATEGORY_MSET)
e1:SetType(EFFECT_TYPE_ACTIVATE)
e1:SetProperty(EFFECT_FLAG_CARD_TARGET)
e1:SetCode(EVENT_FREE_CHAIN)
e1:SetHintTiming(TIMING_BATTLE_PHASE,TIMINGS_CHECK_MONSTER+TIMING_BATTLE_PHASE)
e1:SetTarget(c14087893.target)
e1:SetOperation(c14087893.activate)
c:RegisterEffect(e1)

The hint timing says when the prompt is useful. The target callback decides whether there is a legal face-up monster to Set:

function c14087893.target(e,tp,eg,ep,ev,re,r,rp,chk,chkc)
    if chkc then
        return chkc:IsLocation(LOCATION_MZONE) and c14087893.filter(chkc)
    end
    if chk==0 then
        return Duel.IsExistingTarget(c14087893.filter,tp,LOCATION_MZONE,LOCATION_MZONE,1,nil)
    end
    Duel.Hint(HINT_SELECTMSG,tp,HINTMSG_FACEUP)
    local g=Duel.SelectTarget(tp,c14087893.filter,tp,LOCATION_MZONE,LOCATION_MZONE,1,1,nil)
    Duel.SetOperationInfo(0,CATEGORY_POSITION,g,1,0,0)
end

If no matching monster exists, chk==0 returns false. The client prompt did not create permission by itself.

Responding To A Chain Link

Effects that respond to an activated effect usually use EVENT_CHAINING. Their condition receives the Chain Link being answered through the normal callback arguments. In local scripts, ev is commonly passed to Duel.IsChainNegatable, Duel.NegateActivation, or other Chain functions.

Cyber Dragon Infinity (c10443957.lua) shows the shape:

e3:SetCategory(CATEGORY_NEGATE+CATEGORY_DESTROY)
e3:SetType(EFFECT_TYPE_QUICK_O)
e3:SetCode(EVENT_CHAINING)
e3:SetCountLimit(1)
e3:SetProperty(EFFECT_FLAG_DAMAGE_STEP+EFFECT_FLAG_DAMAGE_CAL)
e3:SetRange(LOCATION_MZONE)
e3:SetCondition(c10443957.discon)
e3:SetCost(c10443957.discost)
e3:SetTarget(c10443957.distg)
e3:SetOperation(c10443957.disop)

function c10443957.discon(e,tp,eg,ep,ev,re,r,rp)
    return not e:GetHandler():IsStatus(STATUS_BATTLE_DESTROYED)
        and Duel.IsChainNegatable(ev)
end

This is a response effect, so EVENT_CHAINING is the event. The condition also checks that the handler is not already marked as battle-destroyed.

MDPro4/YGOPro source note: the current local binding for Duel.IsChainNegatable returns true for any chain count. Local scripts still call it because it documents the intended pattern and keeps compatibility with scripts that expect a chain-negatable check. Do not treat that one call as a complete condition. Keep real card-specific checks around it.

Spell Speed

The local core derives response speed from the effect type and the handler card type:

Script shape	Local speed
Trigger effects and Ignition effects	1
Monster Quick Effects	2
Quick-Play Spell activation	2
Other Spell activation	1
Normal or Continuous Trap activation	2
Counter Trap activation	3

Use the right shape for the card. A monster "(Quick Effect)" is normally an EFFECT_TYPE_QUICK_O or EFFECT_TYPE_QUICK_F effect, not a Counter Trap. A Counter Trap is still a Trap Card activation with EFFECT_TYPE_ACTIVATE; the Trap card type gives it Spell Speed 3.

Damage Step And Damage Calculation

Damage Step legality has two pieces:

Need	Script piece
Open the broad Damage Step window	EFFECT_FLAG_DAMAGE_STEP
Open the damage calculation window	EFFECT_FLAG_DAMAGE_CAL
Decide whether this exact effect should activate there	condition, cost, target checks

The local core filters most activations in the Damage Step unless the effect has EFFECT_FLAG_DAMAGE_STEP. It filters most activations during damage calculation unless the effect has EFFECT_FLAG_DAMAGE_CAL. These flags open the broad window; they do not prove the card's text allows every point inside that window.

Cyber Dragon Infinity uses both flags because its negation effect can be used through those windows:

e3:SetProperty(EFFECT_FLAG_DAMAGE_STEP+EFFECT_FLAG_DAMAGE_CAL)
e3:SetCondition(c10443957.discon)

For effects that are only safe before damage calculation, local scripts often pair a Damage Step property with a condition such as aux.dscon. Keep the condition close to the card text.

Hint Timing Masks

Effect.SetHintTiming stores two timing masks:

e1:SetHintTiming(s_time)
e1:SetHintTiming(s_time,o_time)

The first mask is for the handler controller. The second mask is for the opponent side. If the second argument is omitted, the local core copies the first mask to both sides. When prompts are checked, those two masks are interpreted relative to the handler's current controller.

Common masks include:

Timing	Typical use
TIMING_MAIN_END	Prompt near the end of a Main Phase.
TIMING_BATTLE_PHASE	Prompt during Battle Phase windows.
TIMING_DAMAGE_STEP	Prompt in the Damage Step.
TIMING_DAMAGE_CAL	Prompt during damage calculation.
TIMING_CHAIN_END	Prompt after a Chain finishes resolving.
TIMING_END_PHASE	Prompt near the End Phase.
TIMINGS_CHECK_MONSTER	Prompt around visible monster checks, defined locally as 0x1c0.

Duel.CheckTiming checks whether a timing mask appears in either player's current core hint timing. It is a low-level prompt-window helper, not a replacement for activation legality. No indexed local card script currently calls it directly, so prefer ordinary phase, event, target, and cost checks unless you are writing a helper that really needs the current hint mask.

Opponent-Side Prompts

The two-argument form is useful when a card should mostly prompt the opponent after they do something. Infinite Impermanence (c10045474.lua) uses this:

local e1=Effect.CreateEffect(c)
e1:SetCategory(CATEGORY_DISABLE)
e1:SetType(EFFECT_TYPE_ACTIVATE)
e1:SetProperty(EFFECT_FLAG_CARD_TARGET)
e1:SetCode(EVENT_FREE_CHAIN)
e1:SetHintTiming(0,TIMINGS_CHECK_MONSTER)
e1:SetTarget(c10045474.target)
e1:SetOperation(c10045474.activate)
c:RegisterEffect(e1)

The target callback still checks for a legal opponent monster:

if chk==0 then
    return Duel.IsExistingTarget(aux.NegateMonsterFilter,tp,0,LOCATION_MZONE,1,nil)
end

Its hand activation is not hidden inside hint timing. The script registers a separate effect with EFFECT_TRAP_ACT_IN_HAND and a field-empty condition. That is a good rule of thumb: use hint timing for prompts, and use separate effects or conditions for real exceptions.

Watching Chain Solving

Responding to a Chain Link and watching a Chain Link resolve are different patterns.

EVENT_CHAINING is used before the Chain Link resolves, usually for effects that negate activations. EVENT_CHAIN_SOLVING is used by continuous watcher effects during Chain resolution.

Infinite Impermanence uses EVENT_CHAIN_SOLVING for the temporary column negation it creates after it resolves:

local e5=Effect.CreateEffect(c)
e5:SetType(EFFECT_TYPE_FIELD+EFFECT_TYPE_CONTINUOUS)
e5:SetCode(EVENT_CHAIN_SOLVING)
e5:SetOperation(c10045474.disop)
e5:SetReset(RESET_PHASE+PHASE_END)
e5:SetLabel(c:GetSequence())
Duel.RegisterEffect(e5,tp)

The operation reads Chain information for the resolving Chain Link:

local controller,loc,seq=Duel.GetChainInfo(ev,
    CHAININFO_TRIGGERING_CONTROLER,
    CHAININFO_TRIGGERING_LOCATION,
    CHAININFO_TRIGGERING_SEQUENCE)

Use Duel.GetChainInfo when the script needs data about the specific Chain Link. Do not use a continuous watcher when the card text is supposed to activate as a response.

Common Mistakes

Mistake	Better pattern
Treating SetHintTiming as permission to activate.	Keep legality in type/code/range, condition, cost, and chk==0 target checks.
Using EVENT_FREE_CHAIN for an effect that should answer a Chain Link.	Use EVENT_CHAINING and inspect ev, re, rp, and related Chain data.
Adding Damage Step flags and no Damage Step condition.	Add flags only when needed, then keep the exact timing check in the condition.
Forgetting EFFECT_FLAG_DAMAGE_CAL for damage calculation text.	Use EFFECT_FLAG_DAMAGE_STEP+EFFECT_FLAG_DAMAGE_CAL only when the card is legal there.
Treating Duel.IsChainNegatable as the whole condition in MDPro4.	Add real checks for handler state, card text, player, type, cost, and target rules.
Making a hand-activation exception with hint timing only.	Register the proper exception effect, such as EFFECT_TRAP_ACT_IN_HAND, with its own condition.
Using Duel.CheckTiming instead of a legality check.	Use it only for current hint-mask tests; still check phase, event, action availability, and targets.

Useful API Pages

• Effect.SetType
• Effect.SetCode
• Effect.SetRange
• Effect.SetProperty
• Effect.SetHintTiming
• Duel.CheckTiming
• Duel.GetCurrentPhase
• Duel.IsDamageCalculated
• Duel.IsChainNegatable
• Duel.GetChainInfo
• Duel.NegateActivation
• Duel.NegateEffect
• Duel.SetOperationInfo

Related lessons:

• Activated Effects
• Activation Legality
• Categories, Properties, And Hint Timing
• Client UI And Prompt Behavior
• Cost, Target, And Operation Lifecycle
• Negation and Immunity