diff --git a/internal/flag/error_code.go b/internal/flag/error_code.go
new file mode 100644
index 00000000000..b177f39924e
--- /dev/null
+++ b/internal/flag/error_code.go
@@ -0,0 +1,12 @@
+package flag
+
+// ErrorCode is an enum following the open-feature specs about error code.
+type ErrorCode = string
+
+const (
+	ErrorCodeProviderNotReady ErrorCode = "PROVIDER_NOT_READY"
+	ErrorCodeFlagNotFound     ErrorCode = "FLAG_NOT_FOUND"
+	ErrorCodeParseError       ErrorCode = "PARSE_ERROR"
+	ErrorCodeTypeMismatch     ErrorCode = "TYPE_MISMATCH"
+	ErrorCodeGeneral          ErrorCode = "GENERAL"
+)
diff --git a/internal/flag/evaluation_context.go b/internal/flag/evaluation_context.go
new file mode 100644
index 00000000000..e453957aaf2
--- /dev/null
+++ b/internal/flag/evaluation_context.go
@@ -0,0 +1,11 @@
+package flag
+
+type EvaluationContext struct {
+	// Environment is the name of your current env
+	// this value will be added to the custom information of your user and,
+	// it will allow to create rules based on this environment,
+	Environment string
+
+	// DefaultSdkValue is the default value of the SDK when calling the variation.
+	DefaultSdkValue interface{}
+}
diff --git a/internal/flag/flag.go b/internal/flag/flag.go
index 74974d60428..f6369445188 100644
--- a/internal/flag/flag.go
+++ b/internal/flag/flag.go
@@ -5,9 +5,8 @@ import (
 )
 
 type Flag interface {
-	// Value is returning the Value associate to the flag (True / False / Default ) based
-	// if the flag apply to the user and environment or not.
-	Value(flagName string, user ffuser.User, environment string) (interface{}, string)
+	// Value is returning the Value associate to the flag (True / False / Default )
+	Value(flagName string, user ffuser.User, evaluationCtx EvaluationContext) (interface{}, ResolutionDetails)
 
 	// String display correctly a flag with the right formatting
 	String() string
diff --git a/internal/flag/resolution_detail.go b/internal/flag/resolution_detail.go
new file mode 100644
index 00000000000..66f50cc8139
--- /dev/null
+++ b/internal/flag/resolution_detail.go
@@ -0,0 +1,12 @@
+package flag
+
+type ResolutionDetails struct {
+	// Variant indicates the name of the variant used when evaluating the flag
+	Variant string
+
+	// Reason indicates the reason of the decision
+	Reason ResolutionReason
+
+	// ErrorCode indicates the error code for this evaluation
+	ErrorCode string
+}
diff --git a/internal/flag/resolution_reason.go b/internal/flag/resolution_reason.go
new file mode 100644
index 00000000000..38ae6a50c5c
--- /dev/null
+++ b/internal/flag/resolution_reason.go
@@ -0,0 +1,36 @@
+package flag
+
+// ResolutionReason is an enum following the open-feature specs about resolution reasons.
+type ResolutionReason = string
+
+const (
+	// ReasonTargetingMatch Indicates that the feature flag is targeting
+	// 100% of the targeting audience,
+	// e.g. 100% rollout percentage
+	ReasonTargetingMatch ResolutionReason = "TARGETING_MATCH"
+
+	// ReasonSplit Indicates that the feature flag is targeting
+	// a subset of the targeting audience,
+	// e.g. less than 100% rollout percentage
+	ReasonSplit ResolutionReason = "SPLIT"
+
+	// ReasonDisabled Indicates that the feature flag is disabled
+	ReasonDisabled ResolutionReason = "DISABLED"
+
+	// ReasonDefault Indicates that the feature flag evaluated to the default value
+	ReasonDefault ResolutionReason = "DEFAULT"
+
+	// ReasonStatic	Indicates that the feature flag evaluated to a
+	// static value, for example, the default value for the flag
+	//
+	// Note: Typically means that no dynamic evaluation has been
+	// executed for the feature flag
+	ReasonStatic ResolutionReason = "STATIC"
+
+	// ReasonUnknown Indicates an unknown issue occurred during evaluation
+	ReasonUnknown ResolutionReason = "UNKNOWN"
+
+	// ReasonError Indicates that an error occurred during evaluation
+	// Note: The `errorCode`-field contains the details of this error
+	ReasonError ResolutionReason = "ERROR"
+)
diff --git a/internal/flagstate/flag_state.go b/internal/flagstate/flag_state.go
index 9d8325fbe1f..b66fe88691f 100644
--- a/internal/flagstate/flag_state.go
+++ b/internal/flagstate/flag_state.go
@@ -1,30 +1,16 @@
 package flagstate
 
 import (
-	"time"
+	"github.com/thomaspoignant/go-feature-flag/internal/flag"
 )
 
-// NewFlagState is creating a state for a flag.
-func NewFlagState(
-	trackEvents bool,
-	value interface{},
-	variationType string,
-	failed bool,
-) FlagState {
-	return FlagState{
-		Value:         value,
-		Timestamp:     time.Now().Unix(),
-		VariationType: variationType,
-		Failed:        failed,
-		TrackEvents:   trackEvents,
-	}
-}
-
 // FlagState represents the state of an individual feature flag, with regard to a specific user, when it was called.
 type FlagState struct {
-	Value         interface{} `json:"value"`
-	Timestamp     int64       `json:"timestamp"`
-	VariationType string      `json:"variationType"`
-	TrackEvents   bool        `json:"trackEvents"`
-	Failed        bool        `json:"-"`
+	Value         interface{}           `json:"value"`
+	Timestamp     int64                 `json:"timestamp"`
+	VariationType string                `json:"variationType"`
+	TrackEvents   bool                  `json:"trackEvents"`
+	Failed        bool                  `json:"-"`
+	ErrorCode     flag.ErrorCode        `json:"errorCode"`
+	Reason        flag.ResolutionReason `json:"reason"`
 }
diff --git a/internal/flagv1/flag_data.go b/internal/flagv1/flag_data.go
index b72eb2edf27..83f43ec9543 100644
--- a/internal/flagv1/flag_data.go
+++ b/internal/flagv1/flag_data.go
@@ -7,6 +7,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/thomaspoignant/go-feature-flag/internal/flag"
+
 	"github.com/nikunjy/rules/parser"
 	"github.com/thomaspoignant/go-feature-flag/ffuser"
 	"github.com/thomaspoignant/go-feature-flag/internal/utils"
@@ -56,24 +58,56 @@ type FlagData struct {
 
 // Value is returning the Value associate to the flag (True / False / Default ) based
 // if the toggle apply to the user or not.
-func (f *FlagData) Value(flagName string, user ffuser.User, environment string) (interface{}, string) {
+func (f *FlagData) Value(
+	flagName string,
+	user ffuser.User,
+	evaluationCtx flag.EvaluationContext,
+) (interface{}, flag.ResolutionDetails) {
 	f.updateFlagStage()
 	if f.isExperimentationOver() {
 		// if we have an experimentation that has not started or that is finished we use the default value.
-		return f.getDefault(), VariationDefault
+		return f.getDefault(), flag.ResolutionDetails{
+			Variant: VariationDefault,
+			Reason:  flag.ReasonDefault,
+		}
 	}
 
-	if f.evaluateRule(user, environment) {
+	// Flag disable we cannot apply it.
+	if f.GetDisable() {
+		return evaluationCtx.DefaultSdkValue, flag.ResolutionDetails{
+			Variant: flag.VariationSDKDefault,
+			Reason:  flag.ReasonDisabled,
+		}
+	}
+
+	// we are targeting all users
+	if f.getRule() == "" && f.getPercentage() == 100 {
+		return f.getTrue(), flag.ResolutionDetails{
+			Variant: VariationTrue,
+			Reason:  flag.ReasonTargetingMatch,
+		}
+	}
+
+	if f.evaluateRule(user, evaluationCtx.Environment) {
 		if f.isInPercentage(flagName, user) {
 			// Rule applied and user in the cohort.
-			return f.getTrue(), VariationTrue
+			return f.getTrue(), flag.ResolutionDetails{
+				Variant: VariationTrue,
+				Reason:  flag.ReasonSplit,
+			}
 		}
 		// Rule applied and user not in the cohort.
-		return f.getFalse(), VariationFalse
+		return f.getFalse(), flag.ResolutionDetails{
+			Variant: VariationFalse,
+			Reason:  flag.ReasonSplit,
+		}
 	}
 
-	// Default value is used if the rule does not applied to the user.
-	return f.getDefault(), VariationDefault
+	// Default value is used if the rule does not apply to the user.
+	return f.getDefault(), flag.ResolutionDetails{
+		Variant: VariationDefault,
+		Reason:  flag.ReasonDefault,
+	}
 }
 
 func (f *FlagData) isExperimentationOver() bool {
@@ -103,11 +137,6 @@ func (f *FlagData) isInPercentage(flagName string, user ffuser.User) bool {
 
 // evaluateRule is checking if the rule can apply to a specific user.
 func (f *FlagData) evaluateRule(user ffuser.User, environment string) bool {
-	// Flag disable we cannot apply it.
-	if f.GetDisable() {
-		return false
-	}
-
 	// No rule means that all user can be impacted.
 	if f.getRule() == "" {
 		return true
diff --git a/internal/flagv1/flag_priv_test.go b/internal/flagv1/flag_priv_test.go
index c9fcf626c11..f1989e9146d 100644
--- a/internal/flagv1/flag_priv_test.go
+++ b/internal/flagv1/flag_priv_test.go
@@ -28,16 +28,6 @@ func TestFlag_evaluateRule(t *testing.T) {
 		args   args
 		want   bool
 	}{
-		{
-			name: "Disabled toggle",
-			fields: fields{
-				Disable: true,
-			},
-			args: args{
-				user: ffuser.NewAnonymousUser("random-key"),
-			},
-			want: false,
-		},
 		{
 			name: "Toggle enabled and no rule",
 			fields: fields{
diff --git a/internal/flagv1/flag_pub_test.go b/internal/flagv1/flag_pub_test.go
index ec6cb38a38c..5b92d25130c 100644
--- a/internal/flagv1/flag_pub_test.go
+++ b/internal/flagv1/flag_pub_test.go
@@ -24,12 +24,13 @@ func TestFlag_value(t *testing.T) {
 		Rollout    flagv1.Rollout
 	}
 	type args struct {
-		flagName string
-		user     ffuser.User
+		flagName   string
+		user       ffuser.User
+		sdkDefault string
 	}
 	type want struct {
-		value         interface{}
-		variationType string
+		value             interface{}
+		resolutionDetails flag.ResolutionDetails
 	}
 	tests := []struct {
 		name   string
@@ -38,7 +39,7 @@ func TestFlag_value(t *testing.T) {
 		want   want
 	}{
 		{
-			name: "Rule disable get default value",
+			name: "Flag disable get default value",
 			fields: fields{
 				Disable: true,
 				True:    "true",
@@ -46,12 +47,17 @@ func TestFlag_value(t *testing.T) {
 				Default: "default",
 			},
 			args: args{
-				flagName: "test_689483",
-				user:     ffuser.NewUser("test_689483"),
+				flagName:   "test_689483",
+				user:       ffuser.NewUser("test_689483"),
+				sdkDefault: "defaultSDK",
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "defaultSDK",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flag.VariationSDKDefault,
+					Reason:    flag.ReasonDisabled,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -68,8 +74,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(), // combined hash is 9
 			},
 			want: want{
-				value:         "true",
-				variationType: flagv1.VariationTrue,
+				value: "true",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationTrue,
+					Reason:    flag.ReasonSplit,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -92,8 +102,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
 			},
 			want: want{
-				value:         "true",
-				variationType: flagv1.VariationTrue,
+				value: "true",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationTrue,
+					Reason:    flag.ReasonSplit,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -116,8 +130,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("user66").AddCustom("name", "john").Build(), // combined hash is 9
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "default",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationDefault,
+					Reason:    flag.ReasonDefault,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -140,8 +158,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
 			},
 			want: want{
-				value:         "true",
-				variationType: flagv1.VariationTrue,
+				value: "true",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationTrue,
+					Reason:    flag.ReasonSplit,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -164,8 +186,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("user66").AddCustom("name", "john").Build(), // combined hash is 9
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "default",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationDefault,
+					Reason:    flag.ReasonDefault,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -188,8 +214,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("user66").AddCustom("name", "john").Build(), // combined hash is 9
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "default",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationDefault,
+					Reason:    flag.ReasonDefault,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -212,8 +242,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("user66").AddCustom("name", "john").Build(), // combined hash is 9
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "default",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationDefault,
+					Reason:    flag.ReasonDefault,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -236,8 +270,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
 			},
 			want: want{
-				value:         "true",
-				variationType: flagv1.VariationTrue,
+				value: "true",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationTrue,
+					Reason:    flag.ReasonSplit,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -260,8 +298,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
 			},
 			want: want{
-				value:         "true",
-				variationType: flagv1.VariationTrue,
+				value: "true",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationTrue,
+					Reason:    flag.ReasonSplit,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -284,8 +326,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("user66").AddCustom("name", "john").Build(), // combined hash is 9
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "default",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationDefault,
+					Reason:    flag.ReasonDefault,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -302,8 +348,12 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
 			},
 			want: want{
-				value:         "default",
-				variationType: flagv1.VariationDefault,
+				value: "default",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationDefault,
+					Reason:    flag.ReasonDefault,
+					ErrorCode: "",
+				},
 			},
 		},
 		{
@@ -320,8 +370,33 @@ func TestFlag_value(t *testing.T) {
 				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
 			},
 			want: want{
-				value:         "false",
-				variationType: flagv1.VariationFalse,
+				value: "false",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationFalse,
+					Reason:    flag.ReasonSplit,
+					ErrorCode: "",
+				},
+			},
+		},
+		{
+			name: "Flag target everyone",
+			fields: fields{
+				True:       "true",
+				False:      "false",
+				Default:    "default",
+				Percentage: 100,
+			},
+			args: args{
+				flagName: "test-flag2",
+				user:     ffuser.NewUserBuilder("7e50ee61-06ad-4bb0-9034-38ad7cdea9f5").AddCustom("name", "john").Build(),
+			},
+			want: want{
+				value: "true",
+				resolutionDetails: flag.ResolutionDetails{
+					Variant:   flagv1.VariationTrue,
+					Reason:    flag.ReasonTargetingMatch,
+					ErrorCode: "",
+				},
 			},
 		},
 	}
@@ -337,9 +412,10 @@ func TestFlag_value(t *testing.T) {
 				Rollout:    &tt.fields.Rollout,
 			}
 
-			got, variationType := f.Value(tt.args.flagName, tt.args.user, "")
+			got, resolutionDetails := f.Value(tt.args.flagName, tt.args.user,
+				flag.EvaluationContext{DefaultSdkValue: tt.args.sdkDefault})
 			assert.Equal(t, tt.want.value, got)
-			assert.Equal(t, tt.want.variationType, variationType)
+			assert.Equal(t, tt.want.resolutionDetails, resolutionDetails)
 		})
 	}
 }
@@ -362,15 +438,15 @@ func TestFlag_ProgressiveRollout(t *testing.T) {
 	flagName := "test-flag"
 
 	// We evaluate the same flag multiple time overtime.
-	v, _ := f.Value(flagName, user, "")
+	v, _ := f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, f.GetVariationValue(flagv1.VariationFalse), v)
 
 	time.Sleep(1 * time.Second)
-	v2, _ := f.Value(flagName, user, "")
+	v2, _ := f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, f.GetVariationValue(flagv1.VariationFalse), v2)
 
 	time.Sleep(1 * time.Second)
-	v3, _ := f.Value(flagName, user, "")
+	v3, _ := f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, f.GetVariationValue(flagv1.VariationTrue), v3)
 }
 
@@ -447,43 +523,43 @@ func TestFlag_ScheduledRollout(t *testing.T) {
 	flagName := "test-flag"
 
 	// We evaluate the same flag multiple time overtime.
-	v, _ := f.Value(flagName, user, "")
+	v, _ := f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, f.GetVariationValue(flagv1.VariationFalse), v)
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, "True", v)
 	assert.Equal(t, 1.1, f.GetVersion())
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, "Default2", v)
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, "True2", v)
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{DefaultSdkValue: "Default2"})
 	assert.Equal(t, "Default2", v)
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, "Default2", v)
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, "True2", v)
 
 	time.Sleep(1 * time.Second)
 
-	v, _ = f.Value(flagName, user, "")
+	v, _ = f.Value(flagName, user, flag.EvaluationContext{})
 	assert.Equal(t, "Default2", v)
 }
 
diff --git a/internal/model/variation_result.go b/internal/model/variation_result.go
index 41bc712af8b..43a3c908605 100644
--- a/internal/model/variation_result.go
+++ b/internal/model/variation_result.go
@@ -1,10 +1,14 @@
 package model
 
+import "github.com/thomaspoignant/go-feature-flag/internal/flag"
+
 type VariationResult struct {
-	TrackEvents   bool    `json:"trackEvents"`
-	VariationType string  `json:"variationType"`
-	Failed        bool    `json:"failed"`
-	Version       float64 `json:"version"`
+	TrackEvents   bool                  `json:"trackEvents"`
+	VariationType string                `json:"variationType"`
+	Failed        bool                  `json:"failed"`
+	Version       float64               `json:"version"`
+	Reason        flag.ResolutionReason `json:"reason"`
+	ErrorCode     flag.ErrorCode        `json:"errorCode"`
 }
 
 // BoolVarResult is the internal result format of a bool variation.
diff --git a/testdata/ffclient/all_flags/marshal_json/error_in_flag_0.json b/testdata/ffclient/all_flags/marshal_json/error_in_flag_0.json
index 224ef76ecc3..cd308ff4f65 100644
--- a/testdata/ffclient/all_flags/marshal_json/error_in_flag_0.json
+++ b/testdata/ffclient/all_flags/marshal_json/error_in_flag_0.json
@@ -4,19 +4,25 @@
       "value": false,
       "timestamp": 1622206239,
       "variationType": "Default",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"ERROR",
+      "errorCode": "TYPE_MISMATCH"
     },
     "test-flag1": {
       "value": "true",
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag2": {
       "value": 1,
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag3": {
       "value": [
@@ -25,7 +31,9 @@
       ],
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag4": {
       "value": {
@@ -33,13 +41,17 @@
       },
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag5": {
       "value": 1.1,
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": false
+      "trackEvents": false,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     }
   },
   "valid": false
diff --git a/testdata/ffclient/all_flags/marshal_json/valid_multiple_types.json b/testdata/ffclient/all_flags/marshal_json/valid_multiple_types.json
index 87933074513..94ff9bf786e 100644
--- a/testdata/ffclient/all_flags/marshal_json/valid_multiple_types.json
+++ b/testdata/ffclient/all_flags/marshal_json/valid_multiple_types.json
@@ -4,19 +4,25 @@
       "value": true,
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag1": {
       "value": "true",
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag2": {
       "value": 1,
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag3": {
       "value": [
@@ -25,7 +31,9 @@
       ],
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag4": {
       "value": {
@@ -33,13 +41,17 @@
       },
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": true
+      "trackEvents": true,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     },
     "test-flag5": {
       "value": 1.1,
       "timestamp": 1622206239,
       "variationType": "True",
-      "trackEvents": false
+      "trackEvents": false,
+      "reason":"TARGETING_MATCH",
+      "errorCode": ""
     }
   },
   "valid": true
diff --git a/variation.go b/variation.go
index a1c49c8f978..ec28b5fa496 100644
--- a/variation.go
+++ b/variation.go
@@ -1,7 +1,9 @@
+//nolint:,dupl
 package ffclient
 
 import (
 	"fmt"
+	"time"
 
 	"github.com/thomaspoignant/go-feature-flag/exporter"
 	"github.com/thomaspoignant/go-feature-flag/ffuser"
@@ -153,16 +155,36 @@ func (g *GoFeatureFlag) AllFlagsState(user ffuser.User) flagstate.AllFlags {
 
 	allFlags := flagstate.NewAllFlags()
 	for key, currentFlag := range flags {
-		flagValue, varType := currentFlag.Value(key, user, g.config.Environment)
+		flagValue, varType := currentFlag.Value(key, user, flag.EvaluationContext{
+			Environment:     g.config.Environment,
+			DefaultSdkValue: nil,
+		})
 		switch v := flagValue; v.(type) {
 		case int, float64, bool, string, []interface{}, map[string]interface{}:
-			allFlags.AddFlag(key, flagstate.NewFlagState(currentFlag.GetTrackEvents(), v, varType, false))
+			allFlags.AddFlag(key, flagstate.FlagState{
+				Value:         v,
+				Timestamp:     time.Now().Unix(),
+				VariationType: varType.Variant,
+				TrackEvents:   currentFlag.GetTrackEvents(),
+				Failed:        varType.ErrorCode != "",
+				ErrorCode:     varType.ErrorCode,
+				Reason:        varType.Reason,
+			})
 
 		default:
 			defaultVariationName := currentFlag.GetDefaultVariation()
 			defaultVariationValue := currentFlag.GetVariationValue(defaultVariationName)
 			allFlags.AddFlag(
-				key, flagstate.NewFlagState(currentFlag.GetTrackEvents(), defaultVariationValue, defaultVariationName, true))
+				key,
+				flagstate.FlagState{
+					Value:         defaultVariationValue,
+					Timestamp:     time.Now().Unix(),
+					VariationType: defaultVariationName,
+					TrackEvents:   currentFlag.GetTrackEvents(),
+					Failed:        true,
+					ErrorCode:     flag.ErrorCodeTypeMismatch,
+					Reason:        flag.ReasonError,
+				})
 		}
 	}
 	return allFlags
@@ -186,27 +208,37 @@ func (g *GoFeatureFlag) boolVariation(flagKey string, user ffuser.User, sdkDefau
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		return model.BoolVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res, ok := flagValue.(bool)
 	if !ok {
 		return model.BoolVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f,
+				flag.ResolutionDetails{
+					Variant:   flag.VariationSDKDefault,
+					Reason:    flag.ReasonError,
+					ErrorCode: flag.ErrorCodeTypeMismatch,
+				}),
 		}, fmt.Errorf(errorWrongVariation, flagKey)
 	}
 	return model.BoolVarResult{
 		Value:           res,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}, nil
 }
 
 // intVariation is the internal func that handle the logic of a variation with an int value
-// the result will always contains a valid model.IntVarResult
+// the result will always contain a valid model.IntVarResult
 func (g *GoFeatureFlag) intVariation(flagKey string, user ffuser.User, sdkDefaultValue int,
 ) (model.IntVarResult, error) {
 	if g.config.Offline {
@@ -216,30 +248,39 @@ func (g *GoFeatureFlag) intVariation(flagKey string, user ffuser.User, sdkDefaul
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		return model.IntVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res, ok := flagValue.(int)
 	if !ok {
 		// if this is a float64 we convert it to int
 		if resFloat, okFloat := flagValue.(float64); okFloat {
 			return model.IntVarResult{
 				Value:           int(resFloat),
-				VariationResult: computeVariationResult(f, variationType, false),
+				VariationResult: computeVariationResult(f, resolutionDetails),
 			}, nil
 		}
 
 		return model.IntVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeTypeMismatch,
+			}),
 		}, fmt.Errorf(errorWrongVariation, flagKey)
 	}
 	return model.IntVarResult{
 		Value:           res,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}, nil
 }
 
@@ -254,22 +295,31 @@ func (g *GoFeatureFlag) float64Variation(flagKey string, user ffuser.User, sdkDe
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		return model.Float64VarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res, ok := flagValue.(float64)
 	if !ok {
 		return model.Float64VarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeTypeMismatch,
+			}),
 		}, fmt.Errorf(errorWrongVariation, flagKey)
 	}
 	return model.Float64VarResult{
 		Value:           res,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}, nil
 }
 
@@ -284,22 +334,31 @@ func (g *GoFeatureFlag) stringVariation(flagKey string, user ffuser.User, sdkDef
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		return model.StringVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res, ok := flagValue.(string)
 	if !ok {
 		return model.StringVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeTypeMismatch,
+			}),
 		}, fmt.Errorf(errorWrongVariation, flagKey)
 	}
 	return model.StringVarResult{
 		Value:           res,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}, nil
 }
 
@@ -314,22 +373,31 @@ func (g *GoFeatureFlag) jsonArrayVariation(flagKey string, user ffuser.User, sdk
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		return model.JSONArrayVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res, ok := flagValue.([]interface{})
 	if !ok {
 		return model.JSONArrayVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeTypeMismatch,
+			}),
 		}, fmt.Errorf(errorWrongVariation, flagKey)
 	}
 	return model.JSONArrayVarResult{
 		Value:           res,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}, nil
 }
 
@@ -344,30 +412,41 @@ func (g *GoFeatureFlag) jsonVariation(flagKey string, user ffuser.User, sdkDefau
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		return model.JSONVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res, ok := flagValue.(map[string]interface{})
 	if !ok {
 		return model.JSONVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeTypeMismatch,
+			}),
 		}, fmt.Errorf(errorWrongVariation, flagKey)
 	}
 	return model.JSONVarResult{
 		Value:           res,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}, nil
 }
 
 // computeVariationResult is creating a model.VariationResult
-func computeVariationResult(flag flag.Flag, variationType string, failed bool) model.VariationResult {
+func computeVariationResult(flag flag.Flag, resolutionDetails flag.ResolutionDetails) model.VariationResult {
 	varResult := model.VariationResult{
-		VariationType: variationType,
-		Failed:        failed,
+		VariationType: resolutionDetails.Variant,
+		Failed:        resolutionDetails.ErrorCode != "",
+		Reason:        resolutionDetails.Reason,
+		ErrorCode:     resolutionDetails.ErrorCode,
 	}
 
 	if flag != nil {
@@ -392,17 +471,22 @@ func (g *GoFeatureFlag) RawVariation(flagKey string, user ffuser.User, sdkDefaul
 	f, err := g.getFlagFromCache(flagKey)
 	if err != nil {
 		res := model.RawVarResult{
-			Value:           sdkDefaultValue,
-			VariationResult: computeVariationResult(f, flag.VariationSDKDefault, true),
+			Value: sdkDefaultValue,
+			VariationResult: computeVariationResult(f, flag.ResolutionDetails{
+				Variant:   flag.VariationSDKDefault,
+				Reason:    flag.ReasonError,
+				ErrorCode: flag.ErrorCodeFlagNotFound,
+			}),
 		}
 		g.notifyVariation(flagKey, user, res.VariationResult, res.Value)
 		return res, err
 	}
 
-	flagValue, variationType := f.Value(flagKey, user, g.config.Environment)
+	flagValue, resolutionDetails := f.Value(flagKey, user,
+		flag.EvaluationContext{Environment: g.config.Environment, DefaultSdkValue: sdkDefaultValue})
 	res := model.RawVarResult{
 		Value:           flagValue,
-		VariationResult: computeVariationResult(f, variationType, false),
+		VariationResult: computeVariationResult(f, resolutionDetails),
 	}
 	g.notifyVariation(flagKey, user, res.VariationResult, res.Value)
 	return res, nil
@@ -429,9 +513,9 @@ func (g *GoFeatureFlag) notifyVariation(
 // getFlagFromCache try to get the flag from the cache.
 // It returns an error if the cache is not init or if the flag is not present or disabled.
 func (g *GoFeatureFlag) getFlagFromCache(flagKey string) (flag.Flag, error) {
-	flag, err := g.cache.GetFlag(flagKey)
-	if err != nil || flag.GetDisable() {
-		return flag, fmt.Errorf(errorFlagNotAvailable, flagKey)
+	f, err := g.cache.GetFlag(flagKey)
+	if err != nil {
+		return f, fmt.Errorf(errorFlagNotAvailable, flagKey)
 	}
-	return flag, nil
+	return f, nil
 }
diff --git a/variation_test.go b/variation_test.go
index 5ca9fd0f435..4787907919b 100644
--- a/variation_test.go
+++ b/variation_test.go
@@ -79,7 +79,7 @@ func TestBoolVariation(t *testing.T) {
 				}, nil),
 			},
 			want:        true,
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"true\", variation=\"SdkDefault\"\n",
 		},
 		{
@@ -281,7 +281,7 @@ func TestFloat64Variation(t *testing.T) {
 				}, nil),
 			},
 			want:        120.12,
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"120.12\", variation=\"SdkDefault\"\n",
 		},
 		{
@@ -482,7 +482,7 @@ func TestJSONArrayVariation(t *testing.T) {
 				}, nil),
 			},
 			want:        []interface{}{"toto"},
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"\\[toto\\]\"\n",
 		},
 		{
@@ -697,7 +697,7 @@ func TestJSONVariation(t *testing.T) {
 				}, nil),
 			},
 			want:        map[string]interface{}{"default-notkey": true},
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"map\\[default-notkey:true\\]\", variation=\"SdkDefault\"\n",
 		},
 		{
@@ -880,7 +880,7 @@ func TestStringVariation(t *testing.T) {
 				}, nil),
 			},
 			want:        "default-notkey",
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"default-notkey\", variation=\"SdkDefault\"\n",
 		},
 		{
@@ -1064,7 +1064,7 @@ func TestIntVariation(t *testing.T) {
 				}, nil),
 			},
 			want:        125,
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"125\", variation=\"SdkDefault\"\n",
 		},
 		{
@@ -1424,11 +1424,12 @@ func TestRawVariation(t *testing.T) {
 				Value: true,
 				VariationResult: model.VariationResult{
 					VariationType: flag.VariationSDKDefault,
-					Failed:        true,
+					Failed:        false,
 					TrackEvents:   true,
+					Reason:        flag.ReasonDisabled,
 				},
 			},
-			wantErr:     true,
+			wantErr:     false,
 			expectedLog: "^\\[" + testutils.RFC3339Regex + "\\] user=\"random-key\", flag=\"disable-flag\", value=\"true\", variation=\"SdkDefault\"\n",
 		},
 		{
@@ -1447,6 +1448,8 @@ func TestRawVariation(t *testing.T) {
 					VariationType: flag.VariationSDKDefault,
 					Failed:        true,
 					TrackEvents:   true,
+					Reason:        flag.ReasonError,
+					ErrorCode:     flag.ErrorCodeFlagNotFound,
 				},
 			},
 			wantErr:     true,
@@ -1466,6 +1469,8 @@ func TestRawVariation(t *testing.T) {
 					VariationType: flag.VariationSDKDefault,
 					Failed:        true,
 					TrackEvents:   true,
+					Reason:        flag.ReasonError,
+					ErrorCode:     flag.ErrorCodeFlagNotFound,
 				},
 			},
 			wantErr:     true,
@@ -1491,6 +1496,7 @@ func TestRawVariation(t *testing.T) {
 					VariationType: "Default",
 					Failed:        false,
 					TrackEvents:   true,
+					Reason:        flag.ReasonDefault,
 				},
 			},
 			wantErr:     false,
@@ -1516,6 +1522,7 @@ func TestRawVariation(t *testing.T) {
 					VariationType: "True",
 					Failed:        false,
 					TrackEvents:   true,
+					Reason:        flag.ReasonSplit,
 				},
 			},
 			wantErr:     false,
@@ -1541,6 +1548,7 @@ func TestRawVariation(t *testing.T) {
 					VariationType: "False",
 					Failed:        false,
 					TrackEvents:   true,
+					Reason:        flag.ReasonSplit,
 				},
 			},
 			wantErr:     false,
@@ -1567,6 +1575,7 @@ func TestRawVariation(t *testing.T) {
 					VariationType: "True",
 					Failed:        false,
 					TrackEvents:   false,
+					Reason:        flag.ReasonSplit,
 				},
 			},
 			wantErr:     false,