diff --git a/core/iox/bufferpool.go b/core/iox/bufferpool.go
index 3f3c9102..9304a34e 100644
--- a/core/iox/bufferpool.go
+++ b/core/iox/bufferpool.go
@@ -5,11 +5,13 @@ import (
 	"sync"
 )
 
+// A BufferPool is a pool to buffer bytes.Buffer objects.
 type BufferPool struct {
 	capability int
 	pool       *sync.Pool
 }
 
+// NewBufferPool returns a BufferPool.
 func NewBufferPool(capability int) *BufferPool {
 	return &BufferPool{
 		capability: capability,
@@ -21,12 +23,14 @@ func NewBufferPool(capability int) *BufferPool {
 	}
 }
 
+// Get returns a bytes.Buffer object from bp.
 func (bp *BufferPool) Get() *bytes.Buffer {
 	buf := bp.pool.Get().(*bytes.Buffer)
 	buf.Reset()
 	return buf
 }
 
+// Put returns buf into bp.
 func (bp *BufferPool) Put(buf *bytes.Buffer) {
 	if buf.Cap() < bp.capability {
 		bp.pool.Put(buf)
diff --git a/core/iox/nopcloser.go b/core/iox/nopcloser.go
index 2fefc444..ba27a9f4 100644
--- a/core/iox/nopcloser.go
+++ b/core/iox/nopcloser.go
@@ -10,6 +10,7 @@ func (nopCloser) Close() error {
 	return nil
 }
 
+// NopCloser returns a io.WriteCloser that does nothing on calling Close.
 func NopCloser(w io.Writer) io.WriteCloser {
 	return nopCloser{w}
 }
diff --git a/core/iox/read.go b/core/iox/read.go
index 6c8a76a2..481173e5 100644
--- a/core/iox/read.go
+++ b/core/iox/read.go
@@ -16,9 +16,11 @@ type (
 		omitPrefix    string
 	}
 
+	// TextReadOption defines the method to customize the text reading functions.
 	TextReadOption func(*textReadOptions)
 )
 
+// DupReadCloser returns two io.ReadCloser that read from the first will be written to the second.
 // The first returned reader needs to be read first, because the content
 // read from it will be written to the underlying buffer of the second reader.
 func DupReadCloser(reader io.ReadCloser) (io.ReadCloser, io.ReadCloser) {
@@ -27,6 +29,7 @@ func DupReadCloser(reader io.ReadCloser) (io.ReadCloser, io.ReadCloser) {
 	return ioutil.NopCloser(tee), ioutil.NopCloser(&buf)
 }
 
+// KeepSpace customizes the reading functions to keep leading and tailing spaces.
 func KeepSpace() TextReadOption {
 	return func(o *textReadOptions) {
 		o.keepSpace = true
@@ -49,6 +52,7 @@ func ReadBytes(reader io.Reader, buf []byte) error {
 	return nil
 }
 
+// ReadText reads content from the given file with leading and tailing spaces trimmed.
 func ReadText(filename string) (string, error) {
 	content, err := ioutil.ReadFile(filename)
 	if err != nil {
@@ -58,6 +62,7 @@ func ReadText(filename string) (string, error) {
 	return strings.TrimSpace(string(content)), nil
 }
 
+// ReadTextLines reads the text lines from given file.
 func ReadTextLines(filename string, opts ...TextReadOption) ([]string, error) {
 	var readOpts textReadOptions
 	for _, opt := range opts {
@@ -90,12 +95,14 @@ func ReadTextLines(filename string, opts ...TextReadOption) ([]string, error) {
 	return lines, scanner.Err()
 }
 
+// WithoutBlank customizes the reading functions to ignore blank lines.
 func WithoutBlank() TextReadOption {
 	return func(o *textReadOptions) {
 		o.withoutBlanks = true
 	}
 }
 
+// OmitWithPrefix customizes the reading functions to ignore the lines with given leading prefix.
 func OmitWithPrefix(prefix string) TextReadOption {
 	return func(o *textReadOptions) {
 		o.omitPrefix = prefix
diff --git a/core/iox/textfile.go b/core/iox/textfile.go
index 1cc2cb0b..8feced43 100644
--- a/core/iox/textfile.go
+++ b/core/iox/textfile.go
@@ -8,6 +8,7 @@ import (
 
 const bufSize = 32 * 1024
 
+// CountLines returns the number of lines in file.
 func CountLines(file string) (int, error) {
 	f, err := os.Open(file)
 	if err != nil {
diff --git a/core/iox/textlinescanner.go b/core/iox/textlinescanner.go
index ade9049b..ec28e27a 100644
--- a/core/iox/textlinescanner.go
+++ b/core/iox/textlinescanner.go
@@ -6,6 +6,7 @@ import (
 	"strings"
 )
 
+// A TextLineScanner is a scanner that can scan lines from given reader.
 type TextLineScanner struct {
 	reader  *bufio.Reader
 	hasNext bool
@@ -13,6 +14,7 @@ type TextLineScanner struct {
 	err     error
 }
 
+// NewTextLineScanner returns a TextLineScanner with given reader.
 func NewTextLineScanner(reader io.Reader) *TextLineScanner {
 	return &TextLineScanner{
 		reader:  bufio.NewReader(reader),
@@ -20,6 +22,7 @@ func NewTextLineScanner(reader io.Reader) *TextLineScanner {
 	}
 }
 
+// Scan checks if scanner has more lines to read.
 func (scanner *TextLineScanner) Scan() bool {
 	if !scanner.hasNext {
 		return false
@@ -37,6 +40,7 @@ func (scanner *TextLineScanner) Scan() bool {
 	return true
 }
 
+// Line returns the next available line.
 func (scanner *TextLineScanner) Line() (string, error) {
 	return scanner.line, scanner.err
 }