diff --git a/core/metric/counter.go b/core/metric/counter.go
index f5ca05d2..f34700cf 100644
--- a/core/metric/counter.go
+++ b/core/metric/counter.go
@@ -6,10 +6,14 @@ import (
 )
 
 type (
+	// A CounterVecOpts is an alias of VectorOpts.
 	CounterVecOpts VectorOpts
 
+	// CounterVec interface represents a counter vector.
 	CounterVec interface {
+		// Inc increments labels.
 		Inc(lables ...string)
+		// Add adds labels with v.
 		Add(v float64, labels ...string)
 		close() bool
 	}
@@ -19,6 +23,7 @@ type (
 	}
 )
 
+// NewCounterVec returns a CounterVec.
 func NewCounterVec(cfg *CounterVecOpts) CounterVec {
 	if cfg == nil {
 		return nil
diff --git a/core/metric/gauge.go b/core/metric/gauge.go
index 24834d39..bc449b86 100644
--- a/core/metric/gauge.go
+++ b/core/metric/gauge.go
@@ -6,11 +6,16 @@ import (
 )
 
 type (
+	// GaugeVecOpts is an alias of VectorOpts.
 	GaugeVecOpts VectorOpts
 
-	GuageVec interface {
+	// GaugeVec represents a guage vector.
+	GaugeVec interface {
+		// Set sets v to labels.
 		Set(v float64, labels ...string)
+		// Inc increments labels.
 		Inc(labels ...string)
+		// Add adds v to labels.
 		Add(v float64, labels ...string)
 		close() bool
 	}
@@ -20,7 +25,8 @@ type (
 	}
 )
 
-func NewGaugeVec(cfg *GaugeVecOpts) GuageVec {
+// NewGaugeVec returns a GaugeVec.
+func NewGaugeVec(cfg *GaugeVecOpts) GaugeVec {
 	if cfg == nil {
 		return nil
 	}
diff --git a/core/metric/histogram.go b/core/metric/histogram.go
index d85bcd1a..0f759e91 100644
--- a/core/metric/histogram.go
+++ b/core/metric/histogram.go
@@ -6,6 +6,7 @@ import (
 )
 
 type (
+	// A HistogramVecOpts is a histogram vector options.
 	HistogramVecOpts struct {
 		Namespace string
 		Subsystem string
@@ -15,7 +16,9 @@ type (
 		Buckets   []float64
 	}
 
+	// A HistogramVec interface represents a histogram vector.
 	HistogramVec interface {
+		// Observe adds observation v to labels.
 		Observe(v int64, lables ...string)
 		close() bool
 	}
@@ -25,6 +28,7 @@ type (
 	}
 )
 
+// NewHistogramVec returns a HistogramVec.
 func NewHistogramVec(cfg *HistogramVecOpts) HistogramVec {
 	if cfg == nil {
 		return nil
diff --git a/core/metric/metric.go b/core/metric/metric.go
index 0577f309..f36e0f67 100644
--- a/core/metric/metric.go
+++ b/core/metric/metric.go
@@ -1,6 +1,6 @@
 package metric
 
-// VectorOpts general configuration
+// A VectorOpts is a general configuration.
 type VectorOpts struct {
 	Namespace string
 	Subsystem string