diff --git a/sim/core/apl.go b/sim/core/apl.go
index 73f09312ca..2e14e8eadc 100644
--- a/sim/core/apl.go
+++ b/sim/core/apl.go
@@ -24,6 +24,10 @@ type APLRotation struct {
 	curWarnings          []string
 	prepullWarnings      [][]string
 	priorityListWarnings [][]string
+
+	// Used for detecting infinite loops.
+	prevTime                time.Duration
+	actionsWithoutAdvancing int
 }
 
 func (rot *APLRotation) validationWarning(message string, vals ...interface{}) {
@@ -141,6 +145,8 @@ func (rot *APLRotation) allPrepullActions() []*APLAction {
 
 func (rot *APLRotation) reset(sim *Simulation) {
 	rot.strictSequence = nil
+	rot.actionsWithoutAdvancing = 0
+	rot.prevTime = 0
 	for _, action := range rot.allAPLActions() {
 		action.impl.Reset(sim)
 	}
@@ -157,6 +163,18 @@ func (apl *APLRotation) DoNextAction(sim *Simulation) {
 				if apl.unit.GCD.IsReady(sim) {
 					apl.unit.WaitUntil(sim, sim.CurrentTime)
 				}
+
+				// Detect infinite loops.
+				if sim.CurrentTime == apl.prevTime {
+					apl.actionsWithoutAdvancing++
+					if apl.actionsWithoutAdvancing > 1000 {
+						panic(fmt.Sprintf("[USER_ERROR] Infinite loop detected, current action:\n%s", action))
+					}
+				} else {
+					apl.prevTime = sim.CurrentTime
+					apl.actionsWithoutAdvancing = 0
+				}
+
 				return
 			}
 		}
diff --git a/sim/core/apl_action.go b/sim/core/apl_action.go
index b3f34c53b9..3e18d6f78b 100644
--- a/sim/core/apl_action.go
+++ b/sim/core/apl_action.go
@@ -1,6 +1,8 @@
 package core
 
 import (
+	"fmt"
+
 	"github.com/wowsims/wotlk/sim/core/proto"
 )
 
@@ -24,6 +26,14 @@ func (action *APLAction) GetAllActions() []*APLAction {
 	return actions
 }
 
+func (action *APLAction) String() string {
+	if action.condition == nil {
+		return fmt.Sprintf("ACTION = %s", action.impl)
+	} else {
+		return fmt.Sprintf("IF = %s\nACTION = %s", action.condition, action.impl)
+	}
+}
+
 type APLActionImpl interface {
 	// Returns all inner Actions.
 	GetInnerActions() []*APLAction
@@ -39,8 +49,19 @@ type APLActionImpl interface {
 
 	// Performs the action.
 	Execute(*Simulation)
+
+	// Pretty-print string for debugging.
+	String() string
+}
+
+// Provides empty implementations for the action impl interface functions.
+type defaultAPLActionImpl struct {
 }
 
+func (impl defaultAPLActionImpl) GetInnerActions() []*APLAction { return nil }
+func (impl defaultAPLActionImpl) Finalize(*APLRotation)         {}
+func (impl defaultAPLActionImpl) Reset(*Simulation)             {}
+
 func (rot *APLRotation) newAPLAction(config *proto.APLAction) *APLAction {
 	if config == nil {
 		return nil
diff --git a/sim/core/apl_actions_core.go b/sim/core/apl_actions_core.go
index 4635751263..fdbf80dc7f 100644
--- a/sim/core/apl_actions_core.go
+++ b/sim/core/apl_actions_core.go
@@ -1,10 +1,13 @@
 package core
 
 import (
+	"fmt"
+
 	"github.com/wowsims/wotlk/sim/core/proto"
 )
 
 type APLActionCastSpell struct {
+	defaultAPLActionImpl
 	spell  *Spell
 	target UnitReference
 }
@@ -23,17 +26,18 @@ func (rot *APLRotation) newActionCastSpell(config *proto.APLActionCastSpell) APL
 		target: target,
 	}
 }
-func (action *APLActionCastSpell) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionCastSpell) Finalize(*APLRotation)         {}
-func (action *APLActionCastSpell) Reset(*Simulation)             {}
 func (action *APLActionCastSpell) IsReady(sim *Simulation) bool {
 	return action.spell.CanCast(sim, action.target.Get())
 }
 func (action *APLActionCastSpell) Execute(sim *Simulation) {
 	action.spell.Cast(sim, action.target.Get())
 }
+func (action *APLActionCastSpell) String() string {
+	return fmt.Sprintf("Cast Spell(%s)", action.spell.ActionID)
+}
 
 type APLActionMultidot struct {
+	defaultAPLActionImpl
 	spell      *Spell
 	maxDots    int32
 	maxOverlap APLValue
@@ -67,8 +71,6 @@ func (rot *APLRotation) newActionMultidot(config *proto.APLActionMultidot) APLAc
 		maxOverlap: maxOverlap,
 	}
 }
-func (action *APLActionMultidot) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionMultidot) Finalize(*APLRotation)         {}
 func (action *APLActionMultidot) Reset(*Simulation) {
 	action.nextTarget = nil
 }
@@ -88,8 +90,12 @@ func (action *APLActionMultidot) IsReady(sim *Simulation) bool {
 func (action *APLActionMultidot) Execute(sim *Simulation) {
 	action.spell.Cast(sim, action.nextTarget)
 }
+func (action *APLActionMultidot) String() string {
+	return fmt.Sprintf("Multidot(%s)", action.spell.ActionID)
+}
 
 type APLActionAutocastOtherCooldowns struct {
+	defaultAPLActionImpl
 	character *Character
 
 	nextReadyMCD *MajorCooldown
@@ -101,8 +107,6 @@ func (rot *APLRotation) newActionAutocastOtherCooldowns(config *proto.APLActionA
 		character: unit.Env.Raid.GetPlayerFromUnit(unit).GetCharacter(),
 	}
 }
-func (action *APLActionAutocastOtherCooldowns) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionAutocastOtherCooldowns) Finalize(*APLRotation)         {}
 func (action *APLActionAutocastOtherCooldowns) Reset(*Simulation) {
 	action.nextReadyMCD = nil
 }
@@ -114,8 +118,12 @@ func (action *APLActionAutocastOtherCooldowns) Execute(sim *Simulation) {
 	action.nextReadyMCD.tryActivateHelper(sim, action.character)
 	action.character.UpdateMajorCooldowns()
 }
+func (action *APLActionAutocastOtherCooldowns) String() string {
+	return fmt.Sprintf("Autocast Other Cooldowns")
+}
 
 type APLActionWait struct {
+	defaultAPLActionImpl
 	unit     *Unit
 	duration APLValue
 }
@@ -127,12 +135,12 @@ func (rot *APLRotation) newActionWait(config *proto.APLActionWait) APLActionImpl
 		duration: rot.coerceTo(rot.newAPLValue(config.Duration), proto.APLValueType_ValueTypeDuration),
 	}
 }
-func (action *APLActionWait) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionWait) Finalize(*APLRotation)         {}
-func (action *APLActionWait) Reset(*Simulation)             {}
 func (action *APLActionWait) IsReady(sim *Simulation) bool {
 	return action.duration != nil
 }
 func (action *APLActionWait) Execute(sim *Simulation) {
 	action.unit.WaitUntil(sim, sim.CurrentTime+action.duration.GetDuration(sim))
 }
+func (action *APLActionWait) String() string {
+	return fmt.Sprintf("Wait(%s)", action.duration)
+}
diff --git a/sim/core/apl_actions_misc.go b/sim/core/apl_actions_misc.go
index 8aa7e9c8c9..52b64233bd 100644
--- a/sim/core/apl_actions_misc.go
+++ b/sim/core/apl_actions_misc.go
@@ -1,10 +1,13 @@
 package core
 
 import (
+	"fmt"
+
 	"github.com/wowsims/wotlk/sim/core/proto"
 )
 
 type APLActionChangeTarget struct {
+	defaultAPLActionImpl
 	unit      *Unit
 	newTarget UnitReference
 }
@@ -18,9 +21,6 @@ func (rot *APLRotation) newActionChangeTarget(config *proto.APLActionChangeTarge
 		newTarget: newTarget,
 	}
 }
-func (action *APLActionChangeTarget) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionChangeTarget) Finalize(*APLRotation)         {}
-func (action *APLActionChangeTarget) Reset(*Simulation)             {}
 func (action *APLActionChangeTarget) IsReady(sim *Simulation) bool {
 	return action.unit.CurrentTarget != action.newTarget.Get()
 }
@@ -30,8 +30,12 @@ func (action *APLActionChangeTarget) Execute(sim *Simulation) {
 	}
 	action.unit.CurrentTarget = action.newTarget.Get()
 }
+func (action *APLActionChangeTarget) String() string {
+	return fmt.Sprintf("Change Target(%s)", action.newTarget.Get().Label)
+}
 
 type APLActionCancelAura struct {
+	defaultAPLActionImpl
 	aura *Aura
 }
 
@@ -44,9 +48,6 @@ func (rot *APLRotation) newActionCancelAura(config *proto.APLActionCancelAura) A
 		aura: aura.Get(),
 	}
 }
-func (action *APLActionCancelAura) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionCancelAura) Finalize(*APLRotation)         {}
-func (action *APLActionCancelAura) Reset(*Simulation)             {}
 func (action *APLActionCancelAura) IsReady(sim *Simulation) bool {
 	return action.aura.IsActive()
 }
@@ -56,8 +57,12 @@ func (action *APLActionCancelAura) Execute(sim *Simulation) {
 	}
 	action.aura.Deactivate(sim)
 }
+func (action *APLActionCancelAura) String() string {
+	return fmt.Sprintf("Cancel Aura(%s)", action.aura.ActionID)
+}
 
 type APLActionTriggerICD struct {
+	defaultAPLActionImpl
 	aura *Aura
 }
 
@@ -70,9 +75,6 @@ func (rot *APLRotation) newActionTriggerICD(config *proto.APLActionTriggerICD) A
 		aura: aura.Get(),
 	}
 }
-func (action *APLActionTriggerICD) GetInnerActions() []*APLAction { return nil }
-func (action *APLActionTriggerICD) Finalize(*APLRotation)         {}
-func (action *APLActionTriggerICD) Reset(*Simulation)             {}
 func (action *APLActionTriggerICD) IsReady(sim *Simulation) bool {
 	return action.aura.IsActive()
 }
@@ -82,3 +84,6 @@ func (action *APLActionTriggerICD) Execute(sim *Simulation) {
 	}
 	action.aura.Icd.Use(sim)
 }
+func (action *APLActionTriggerICD) String() string {
+	return fmt.Sprintf("Trigger ICD(%s)", action.aura.ActionID)
+}
diff --git a/sim/core/apl_actions_sequences.go b/sim/core/apl_actions_sequences.go
index df66c2c93a..f36b587c64 100644
--- a/sim/core/apl_actions_sequences.go
+++ b/sim/core/apl_actions_sequences.go
@@ -1,10 +1,14 @@
 package core
 
 import (
+	"fmt"
+	"strings"
+
 	"github.com/wowsims/wotlk/sim/core/proto"
 )
 
 type APLActionSequence struct {
+	defaultAPLActionImpl
 	unit    *Unit
 	name    string
 	actions []*APLAction
@@ -41,8 +45,12 @@ func (action *APLActionSequence) Execute(sim *Simulation) {
 	action.actions[action.curIdx].Execute(sim)
 	action.curIdx++
 }
+func (action *APLActionSequence) String() string {
+	return "Sequence(" + strings.Join(MapSlice(action.actions, func(subaction *APLAction) string { return fmt.Sprintf("(%s)", subaction) }), "+") + ")"
+}
 
 type APLActionResetSequence struct {
+	defaultAPLActionImpl
 	unit     *Unit
 	name     string
 	sequence *APLActionSequence
@@ -58,7 +66,6 @@ func (rot *APLRotation) newActionResetSequence(config *proto.APLActionResetSeque
 		name: config.SequenceName,
 	}
 }
-func (action *APLActionResetSequence) GetInnerActions() []*APLAction { return nil }
 func (action *APLActionResetSequence) Finalize(rot *APLRotation) {
 	for _, otherAction := range rot.allAPLActions() {
 		if sequence, ok := otherAction.impl.(*APLActionSequence); ok && sequence.name == action.name {
@@ -68,15 +75,18 @@ func (action *APLActionResetSequence) Finalize(rot *APLRotation) {
 	}
 	rot.validationWarning("No sequence with name: '%s'", action.name)
 }
-func (action *APLActionResetSequence) Reset(*Simulation) {}
 func (action *APLActionResetSequence) IsReady(sim *Simulation) bool {
 	return action.sequence != nil
 }
 func (action *APLActionResetSequence) Execute(sim *Simulation) {
 	action.sequence.curIdx = 0
 }
+func (action *APLActionResetSequence) String() string {
+	return fmt.Sprintf("Reset Sequence(name = '%s')", action.name)
+}
 
 type APLActionStrictSequence struct {
+	defaultAPLActionImpl
 	unit    *Unit
 	actions []*APLAction
 	curIdx  int
@@ -128,3 +138,6 @@ func (action *APLActionStrictSequence) Execute(sim *Simulation) {
 		action.unit.Rotation.strictSequence = nil
 	}
 }
+func (action *APLActionStrictSequence) String() string {
+	return "Strict Sequence(" + strings.Join(MapSlice(action.actions, func(subaction *APLAction) string { return fmt.Sprintf("(%s)", subaction) }), "+") + ")"
+}
diff --git a/sim/core/apl_helpers.go b/sim/core/apl_helpers.go
index 0a7443effb..f5f3e8a740 100644
--- a/sim/core/apl_helpers.go
+++ b/sim/core/apl_helpers.go
@@ -21,6 +21,10 @@ func (ur UnitReference) Get() *Unit {
 	}
 }
 
+func (ur *UnitReference) String() string {
+	return ur.Get().Label
+}
+
 func NewUnitReference(ref *proto.UnitReference, contextUnit *Unit) UnitReference {
 	if ref == nil || ref.Type == proto.UnitReference_Unknown {
 		return UnitReference{}
@@ -70,6 +74,10 @@ func (ar *AuraReference) Get() *Aura {
 	}
 }
 
+func (ar *AuraReference) String() string {
+	return ar.Get().ActionID.String()
+}
+
 func newAuraReferenceHelper(sourceUnit UnitReference, auraId *proto.ActionID, auraGetter func(*Unit, ActionID) *Aura) AuraReference {
 	if sourceUnit.Get() == nil {
 		return AuraReference{}
diff --git a/sim/core/apl_value.go b/sim/core/apl_value.go
index 6c229351d1..202d9feb90 100644
--- a/sim/core/apl_value.go
+++ b/sim/core/apl_value.go
@@ -17,6 +17,9 @@ type APLValue interface {
 	GetFloat(*Simulation) float64
 	GetDuration(*Simulation) time.Duration
 	GetString(*Simulation) string
+
+	// Pretty-print string for debugging.
+	String() string
 }
 
 // Provides empty implementations for the GetX() value interface functions.
diff --git a/sim/core/apl_values_aura.go b/sim/core/apl_values_aura.go
index 5db388d062..0e61b89197 100644
--- a/sim/core/apl_values_aura.go
+++ b/sim/core/apl_values_aura.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -26,6 +27,9 @@ func (value *APLValueAuraIsActive) Type() proto.APLValueType {
 func (value *APLValueAuraIsActive) GetBool(sim *Simulation) bool {
 	return value.aura.Get().IsActive()
 }
+func (value *APLValueAuraIsActive) String() string {
+	return fmt.Sprintf("Aura Is Active(%s)", value.aura.String())
+}
 
 type APLValueAuraRemainingTime struct {
 	defaultAPLValueImpl
@@ -47,6 +51,9 @@ func (value *APLValueAuraRemainingTime) Type() proto.APLValueType {
 func (value *APLValueAuraRemainingTime) GetDuration(sim *Simulation) time.Duration {
 	return value.aura.Get().RemainingDuration(sim)
 }
+func (value *APLValueAuraRemainingTime) String() string {
+	return fmt.Sprintf("Aura Remaining Time(%s)", value.aura.String())
+}
 
 type APLValueAuraNumStacks struct {
 	defaultAPLValueImpl
@@ -72,6 +79,9 @@ func (value *APLValueAuraNumStacks) Type() proto.APLValueType {
 func (value *APLValueAuraNumStacks) GetInt(sim *Simulation) int32 {
 	return value.aura.Get().GetStacks()
 }
+func (value *APLValueAuraNumStacks) String() string {
+	return fmt.Sprintf("Aura Num Stacks(%s)", value.aura.String())
+}
 
 type APLValueAuraInternalCooldown struct {
 	defaultAPLValueImpl
@@ -93,3 +103,6 @@ func (value *APLValueAuraInternalCooldown) Type() proto.APLValueType {
 func (value *APLValueAuraInternalCooldown) GetDuration(sim *Simulation) time.Duration {
 	return value.aura.Get().Icd.TimeToReady(sim)
 }
+func (value *APLValueAuraInternalCooldown) String() string {
+	return fmt.Sprintf("Aura ICD(%s)", value.aura.String())
+}
diff --git a/sim/core/apl_values_auto_attacks.go b/sim/core/apl_values_auto_attacks.go
index bf5dde3bb2..31be9710e6 100644
--- a/sim/core/apl_values_auto_attacks.go
+++ b/sim/core/apl_values_auto_attacks.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -22,3 +23,6 @@ func (value *APLValueAutoTimeToNext) Type() proto.APLValueType {
 func (value *APLValueAutoTimeToNext) GetDuration(sim *Simulation) time.Duration {
 	return MaxDuration(0, value.unit.AutoAttacks.NextAttackAt()-sim.CurrentTime)
 }
+func (value *APLValueAutoTimeToNext) String() string {
+	return fmt.Sprintf("Auto Time To Next")
+}
diff --git a/sim/core/apl_values_core.go b/sim/core/apl_values_core.go
index 08d85a4289..ea477a6b84 100644
--- a/sim/core/apl_values_core.go
+++ b/sim/core/apl_values_core.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -26,6 +27,9 @@ func (value *APLValueDotIsActive) Type() proto.APLValueType {
 func (value *APLValueDotIsActive) GetBool(sim *Simulation) bool {
 	return value.dot.IsActive()
 }
+func (value *APLValueDotIsActive) String() string {
+	return fmt.Sprintf("Dot Is Active(%s)", value.dot.Spell.ActionID)
+}
 
 type APLValueDotRemainingTime struct {
 	defaultAPLValueImpl
@@ -47,3 +51,6 @@ func (value *APLValueDotRemainingTime) Type() proto.APLValueType {
 func (value *APLValueDotRemainingTime) GetDuration(sim *Simulation) time.Duration {
 	return value.dot.RemainingDuration(sim)
 }
+func (value *APLValueDotRemainingTime) String() string {
+	return fmt.Sprintf("Dot Remaining Time(%s)", value.dot.Spell.ActionID)
+}
diff --git a/sim/core/apl_values_encounter.go b/sim/core/apl_values_encounter.go
index 29c1b8737e..250a5f9a52 100644
--- a/sim/core/apl_values_encounter.go
+++ b/sim/core/apl_values_encounter.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -19,6 +20,9 @@ func (value *APLValueCurrentTime) Type() proto.APLValueType {
 func (value *APLValueCurrentTime) GetDuration(sim *Simulation) time.Duration {
 	return sim.CurrentTime
 }
+func (value *APLValueCurrentTime) String() string {
+	return fmt.Sprintf("Current Time")
+}
 
 type APLValueCurrentTimePercent struct {
 	defaultAPLValueImpl
@@ -33,6 +37,9 @@ func (value *APLValueCurrentTimePercent) Type() proto.APLValueType {
 func (value *APLValueCurrentTimePercent) GetFloat(sim *Simulation) float64 {
 	return sim.CurrentTime.Seconds() / sim.Duration.Seconds()
 }
+func (value *APLValueCurrentTimePercent) String() string {
+	return fmt.Sprintf("Current Time %%")
+}
 
 type APLValueRemainingTime struct {
 	defaultAPLValueImpl
@@ -47,6 +54,9 @@ func (value *APLValueRemainingTime) Type() proto.APLValueType {
 func (value *APLValueRemainingTime) GetDuration(sim *Simulation) time.Duration {
 	return sim.GetRemainingDuration()
 }
+func (value *APLValueRemainingTime) String() string {
+	return fmt.Sprintf("Remaining Time")
+}
 
 type APLValueRemainingTimePercent struct {
 	defaultAPLValueImpl
@@ -61,6 +71,9 @@ func (value *APLValueRemainingTimePercent) Type() proto.APLValueType {
 func (value *APLValueRemainingTimePercent) GetFloat(sim *Simulation) float64 {
 	return sim.GetRemainingDurationPercent()
 }
+func (value *APLValueRemainingTimePercent) String() string {
+	return fmt.Sprintf("Remaining Time %%")
+}
 
 type APLValueNumberTargets struct {
 	defaultAPLValueImpl
@@ -75,6 +88,9 @@ func (value *APLValueNumberTargets) Type() proto.APLValueType {
 func (value *APLValueNumberTargets) GetInt(sim *Simulation) int32 {
 	return sim.GetNumTargets()
 }
+func (value *APLValueNumberTargets) String() string {
+	return fmt.Sprintf("Num Targets")
+}
 
 type APLValueIsExecutePhase struct {
 	defaultAPLValueImpl
@@ -103,3 +119,6 @@ func (value *APLValueIsExecutePhase) GetBool(sim *Simulation) bool {
 		panic("Should never reach here")
 	}
 }
+func (value *APLValueIsExecutePhase) String() string {
+	return fmt.Sprintf("Is Execute Phase")
+}
diff --git a/sim/core/apl_values_gcd.go b/sim/core/apl_values_gcd.go
index 5f185b98ef..2c0bb71be3 100644
--- a/sim/core/apl_values_gcd.go
+++ b/sim/core/apl_values_gcd.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -22,6 +23,9 @@ func (value *APLValueGCDIsReady) Type() proto.APLValueType {
 func (value *APLValueGCDIsReady) GetBool(sim *Simulation) bool {
 	return value.unit.GCD.IsReady(sim)
 }
+func (value *APLValueGCDIsReady) String() string {
+	return fmt.Sprintf("GCD Is Ready")
+}
 
 type APLValueGCDTimeToReady struct {
 	defaultAPLValueImpl
@@ -39,3 +43,6 @@ func (value *APLValueGCDTimeToReady) Type() proto.APLValueType {
 func (value *APLValueGCDTimeToReady) GetDuration(sim *Simulation) time.Duration {
 	return value.unit.GCD.TimeToReady(sim)
 }
+func (value *APLValueGCDTimeToReady) String() string {
+	return fmt.Sprintf("GCD Time To Ready")
+}
diff --git a/sim/core/apl_values_operators.go b/sim/core/apl_values_operators.go
index 11ce6d94dd..577f8c1d2e 100644
--- a/sim/core/apl_values_operators.go
+++ b/sim/core/apl_values_operators.go
@@ -3,6 +3,7 @@ package core
 import (
 	"fmt"
 	"strconv"
+	"strings"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -74,6 +75,9 @@ func (value *APLValueConst) GetDuration(sim *Simulation) time.Duration {
 func (value *APLValueConst) GetString(sim *Simulation) string {
 	return value.stringVal
 }
+func (value *APLValueConst) String() string {
+	return value.stringVal
+}
 
 type APLValueCoerced struct {
 	valueType proto.APLValueType
@@ -166,6 +170,9 @@ func (value APLValueCoerced) GetString(sim *Simulation) string {
 	}
 	return ""
 }
+func (value *APLValueCoerced) String() string {
+	return value.inner.String()
+}
 
 // Wraps a value so that it is converted into a Boolean.
 func (rot *APLRotation) coerceTo(value APLValue, newType proto.APLValueType) APLValue {
@@ -310,6 +317,9 @@ func (value *APLValueCompare) GetBool(sim *Simulation) bool {
 	}
 	return false
 }
+func (value *APLValueCompare) String() string {
+	return fmt.Sprintf("%s %s %s", value.lhs, value.op, value.rhs)
+}
 
 type APLValueMath struct {
 	defaultAPLValueImpl
@@ -404,6 +414,9 @@ func (value *APLValueMath) GetDuration(sim *Simulation) time.Duration {
 	}
 	return 0
 }
+func (value *APLValueMath) String() string {
+	return fmt.Sprintf("%s %s %s", value.lhs, value.op, value.rhs)
+}
 
 type APLValueAnd struct {
 	defaultAPLValueImpl
@@ -433,6 +446,9 @@ func (value *APLValueAnd) GetBool(sim *Simulation) bool {
 	}
 	return true
 }
+func (value *APLValueAnd) String() string {
+	return strings.Join(MapSlice(value.vals, func(subvalue APLValue) string { return fmt.Sprintf("(%s)", subvalue) }), " AND ")
+}
 
 type APLValueOr struct {
 	defaultAPLValueImpl
@@ -462,6 +478,9 @@ func (value *APLValueOr) GetBool(sim *Simulation) bool {
 	}
 	return false
 }
+func (value *APLValueOr) String() string {
+	return strings.Join(MapSlice(value.vals, func(subvalue APLValue) string { return fmt.Sprintf("(%s)", subvalue) }), " OR ")
+}
 
 type APLValueNot struct {
 	defaultAPLValueImpl
@@ -483,3 +502,6 @@ func (value *APLValueNot) Type() proto.APLValueType {
 func (value *APLValueNot) GetBool(sim *Simulation) bool {
 	return !value.val.GetBool(sim)
 }
+func (value *APLValueNot) String() string {
+	return fmt.Sprintf("Not(%s)", value.val)
+}
diff --git a/sim/core/apl_values_resources.go b/sim/core/apl_values_resources.go
index 9e2f02fa10..dbafec7cde 100644
--- a/sim/core/apl_values_resources.go
+++ b/sim/core/apl_values_resources.go
@@ -1,6 +1,8 @@
 package core
 
 import (
+	"fmt"
+
 	"github.com/wowsims/wotlk/sim/core/proto"
 )
 
@@ -28,6 +30,9 @@ func (value *APLValueCurrentHealth) Type() proto.APLValueType {
 func (value *APLValueCurrentHealth) GetFloat(sim *Simulation) float64 {
 	return value.unit.Get().CurrentHealth()
 }
+func (value *APLValueCurrentHealth) String() string {
+	return fmt.Sprintf("Current Health")
+}
 
 type APLValueCurrentHealthPercent struct {
 	defaultAPLValueImpl
@@ -53,6 +58,9 @@ func (value *APLValueCurrentHealthPercent) Type() proto.APLValueType {
 func (value *APLValueCurrentHealthPercent) GetFloat(sim *Simulation) float64 {
 	return value.unit.Get().CurrentHealthPercent()
 }
+func (value *APLValueCurrentHealthPercent) String() string {
+	return fmt.Sprintf("Current Health %%")
+}
 
 type APLValueCurrentMana struct {
 	defaultAPLValueImpl
@@ -78,6 +86,9 @@ func (value *APLValueCurrentMana) Type() proto.APLValueType {
 func (value *APLValueCurrentMana) GetFloat(sim *Simulation) float64 {
 	return value.unit.Get().CurrentMana()
 }
+func (value *APLValueCurrentMana) String() string {
+	return fmt.Sprintf("Current Mana")
+}
 
 type APLValueCurrentManaPercent struct {
 	defaultAPLValueImpl
@@ -103,6 +114,9 @@ func (value *APLValueCurrentManaPercent) Type() proto.APLValueType {
 func (value *APLValueCurrentManaPercent) GetFloat(sim *Simulation) float64 {
 	return value.unit.Get().CurrentManaPercent()
 }
+func (value *APLValueCurrentManaPercent) String() string {
+	return fmt.Sprintf("Current Mana %%")
+}
 
 type APLValueCurrentRage struct {
 	defaultAPLValueImpl
@@ -125,6 +139,9 @@ func (value *APLValueCurrentRage) Type() proto.APLValueType {
 func (value *APLValueCurrentRage) GetFloat(sim *Simulation) float64 {
 	return value.unit.CurrentRage()
 }
+func (value *APLValueCurrentRage) String() string {
+	return fmt.Sprintf("Current Rage")
+}
 
 type APLValueCurrentEnergy struct {
 	defaultAPLValueImpl
@@ -147,6 +164,9 @@ func (value *APLValueCurrentEnergy) Type() proto.APLValueType {
 func (value *APLValueCurrentEnergy) GetFloat(sim *Simulation) float64 {
 	return value.unit.CurrentEnergy()
 }
+func (value *APLValueCurrentEnergy) String() string {
+	return fmt.Sprintf("Current Energy")
+}
 
 type APLValueCurrentComboPoints struct {
 	defaultAPLValueImpl
@@ -169,6 +189,9 @@ func (value *APLValueCurrentComboPoints) Type() proto.APLValueType {
 func (value *APLValueCurrentComboPoints) GetInt(sim *Simulation) int32 {
 	return value.unit.ComboPoints()
 }
+func (value *APLValueCurrentComboPoints) String() string {
+	return fmt.Sprintf("Current Combo Points")
+}
 
 type APLValueCurrentRunicPower struct {
 	defaultAPLValueImpl
@@ -191,3 +214,6 @@ func (value *APLValueCurrentRunicPower) Type() proto.APLValueType {
 func (value *APLValueCurrentRunicPower) GetInt(sim *Simulation) int32 {
 	return int32(value.unit.CurrentRunicPower())
 }
+func (value *APLValueCurrentRunicPower) String() string {
+	return fmt.Sprintf("Current Runic Power")
+}
diff --git a/sim/core/apl_values_runes.go b/sim/core/apl_values_runes.go
index 8048855cc8..66d6627ac1 100644
--- a/sim/core/apl_values_runes.go
+++ b/sim/core/apl_values_runes.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -39,6 +40,9 @@ func (value *APLValueCurrentRuneCount) GetInt(sim *Simulation) int32 {
 	}
 	return 0
 }
+func (value *APLValueCurrentRuneCount) String() string {
+	return fmt.Sprintf("Current Rune Count(%s)", value.runeType)
+}
 
 type APLValueCurrentNonDeathRuneCount struct {
 	defaultAPLValueImpl
@@ -71,6 +75,9 @@ func (value *APLValueCurrentNonDeathRuneCount) GetInt(sim *Simulation) int32 {
 	}
 	return 0
 }
+func (value *APLValueCurrentNonDeathRuneCount) String() string {
+	return fmt.Sprintf("Current Non-Death Rune Count(%s)", value.runeType)
+}
 
 type APLValueCurrentRuneActive struct {
 	defaultAPLValueImpl
@@ -95,6 +102,9 @@ func (value *APLValueCurrentRuneActive) Type() proto.APLValueType {
 func (value *APLValueCurrentRuneActive) GetBool(sim *Simulation) bool {
 	return value.unit.RuneIsActive(value.runeSlot)
 }
+func (value *APLValueCurrentRuneActive) String() string {
+	return fmt.Sprintf("Current Rune Active(%d)", value.runeSlot)
+}
 
 type APLValueCurrentRuneDeath struct {
 	defaultAPLValueImpl
@@ -119,6 +129,9 @@ func (value *APLValueCurrentRuneDeath) Type() proto.APLValueType {
 func (value *APLValueCurrentRuneDeath) GetBool(sim *Simulation) bool {
 	return value.unit.RuneIsDeath(int8(value.runeSlot))
 }
+func (value *APLValueCurrentRuneDeath) String() string {
+	return fmt.Sprintf("Current Rune Death(%d)", value.runeSlot)
+}
 
 type APLValueRuneCooldown struct {
 	defaultAPLValueImpl
@@ -151,6 +164,9 @@ func (value *APLValueRuneCooldown) GetDuration(sim *Simulation) time.Duration {
 	}
 	return 0
 }
+func (value *APLValueRuneCooldown) String() string {
+	return fmt.Sprintf("Rune Cooldoean(%s)", value.runeType)
+}
 
 type APLValueNextRuneCooldown struct {
 	defaultAPLValueImpl
@@ -183,3 +199,6 @@ func (value *APLValueNextRuneCooldown) GetDuration(sim *Simulation) time.Duratio
 	}
 	return 0
 }
+func (value *APLValueNextRuneCooldown) String() string {
+	return fmt.Sprintf("Next Rune Cooldoean(%s)", value.runeType)
+}
diff --git a/sim/core/apl_values_spell.go b/sim/core/apl_values_spell.go
index 316f360133..81a8e03031 100644
--- a/sim/core/apl_values_spell.go
+++ b/sim/core/apl_values_spell.go
@@ -1,6 +1,7 @@
 package core
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/wowsims/wotlk/sim/core/proto"
@@ -26,6 +27,9 @@ func (value *APLValueSpellCanCast) Type() proto.APLValueType {
 func (value *APLValueSpellCanCast) GetBool(sim *Simulation) bool {
 	return value.spell.CanCast(sim, value.spell.Unit.CurrentTarget)
 }
+func (value *APLValueSpellCanCast) String() string {
+	return fmt.Sprintf("Can Cast(%s)", value.spell.ActionID)
+}
 
 type APLValueSpellIsReady struct {
 	defaultAPLValueImpl
@@ -47,6 +51,9 @@ func (value *APLValueSpellIsReady) Type() proto.APLValueType {
 func (value *APLValueSpellIsReady) GetBool(sim *Simulation) bool {
 	return value.spell.IsReady(sim)
 }
+func (value *APLValueSpellIsReady) String() string {
+	return fmt.Sprintf("Is Ready(%s)", value.spell.ActionID)
+}
 
 type APLValueSpellTimeToReady struct {
 	defaultAPLValueImpl
@@ -68,6 +75,9 @@ func (value *APLValueSpellTimeToReady) Type() proto.APLValueType {
 func (value *APLValueSpellTimeToReady) GetDuration(sim *Simulation) time.Duration {
 	return value.spell.TimeToReady(sim)
 }
+func (value *APLValueSpellTimeToReady) String() string {
+	return fmt.Sprintf("Time To Ready(%s)", value.spell.ActionID)
+}
 
 type APLValueSpellCastTime struct {
 	defaultAPLValueImpl
@@ -89,6 +99,9 @@ func (value *APLValueSpellCastTime) Type() proto.APLValueType {
 func (value *APLValueSpellCastTime) GetDuration(sim *Simulation) time.Duration {
 	return value.spell.Unit.ApplyCastSpeedForSpell(value.spell.DefaultCast.CastTime, value.spell)
 }
+func (value *APLValueSpellCastTime) String() string {
+	return fmt.Sprintf("Cast Time(%s)", value.spell.ActionID)
+}
 
 type APLValueSpellChannelTime struct {
 	defaultAPLValueImpl
@@ -110,6 +123,9 @@ func (value *APLValueSpellChannelTime) Type() proto.APLValueType {
 func (value *APLValueSpellChannelTime) GetDuration(sim *Simulation) time.Duration {
 	return value.spell.Unit.ApplyCastSpeedForSpell(value.spell.DefaultCast.ChannelTime, value.spell)
 }
+func (value *APLValueSpellChannelTime) String() string {
+	return fmt.Sprintf("Channel Time(%s)", value.spell.ActionID)
+}
 
 type APLValueSpellTravelTime struct {
 	defaultAPLValueImpl
@@ -131,3 +147,6 @@ func (value *APLValueSpellTravelTime) Type() proto.APLValueType {
 func (value *APLValueSpellTravelTime) GetDuration(sim *Simulation) time.Duration {
 	return time.Duration(float64(time.Second) * value.spell.Unit.DistanceFromTarget / value.spell.MissileSpeed)
 }
+func (value *APLValueSpellTravelTime) String() string {
+	return fmt.Sprintf("Travel Time(%s)", value.spell.ActionID)
+}
diff --git a/ui/core/sim_ui.ts b/ui/core/sim_ui.ts
index 0d18515918..c99ef34915 100644
--- a/ui/core/sim_ui.ts
+++ b/ui/core/sim_ui.ts
@@ -277,6 +277,12 @@ export abstract class SimUI extends Component {
 		}
 
 		const errorStr = (error as SimError).errorStr;
+		if (errorStr.startsWith('[USER_ERROR] ')) {
+			const alertStr = errorStr.substring('[USER_ERROR] '.length);
+			alert(alertStr);
+			return;
+		}
+
 		if (window.confirm('Simulation Failure:\n' + errorStr + '\nPress Ok to file crash report')) {
 			// Splice out just the line numbers
 			const hash = this.hashCode(errorStr);