diff --git a/completion.go b/completion.go
index 1a379c5..01417da 100644
--- a/completion.go
+++ b/completion.go
@@ -16,11 +16,13 @@ const (
 	completionMargin = leftMargin + rightMargin
 )
 
+// Suggest is printed when completing.
 type Suggest struct {
 	Text        string
 	Description string
 }
 
+// CompletionManager manages which suggestion is now selected.
 type CompletionManager struct {
 	selected  int // -1 means nothing one is selected.
 	tmp       []Suggest
@@ -28,6 +30,7 @@ type CompletionManager struct {
 	completer Completer
 }
 
+// GetSelectedSuggestion returns the selected item.
 func (c *CompletionManager) GetSelectedSuggestion() (s Suggest, ok bool) {
 	if c.selected == -1 {
 		return Suggest{}, false
@@ -39,33 +42,39 @@ func (c *CompletionManager) GetSelectedSuggestion() (s Suggest, ok bool) {
 	return c.tmp[c.selected], true
 }
 
+// GetSelectedSuggestion returns the list of suggestion.
 func (c *CompletionManager) GetSuggestions() []Suggest {
 	return c.tmp
 }
 
+// Reset to select nothing.
 func (c *CompletionManager) Reset() {
 	c.selected = -1
 	c.Update(*NewDocument())
 	return
 }
 
+// Update to update the suggestions.
 func (c *CompletionManager) Update(in Document) {
 	c.tmp = c.completer(in)
 	return
 }
 
+// Previous to select the previous suggestion item.
 func (c *CompletionManager) Previous() {
 	c.selected--
 	c.update()
 	return
 }
 
+// Next to select the next suggestion item.
 func (c *CompletionManager) Next() {
 	c.selected++
 	c.update()
 	return
 }
 
+// Completing returns whether the CompletionManager selects something one.
 func (c *CompletionManager) Completing() bool {
 	return c.selected != -1
 }
@@ -145,6 +154,7 @@ func formatSuggestions(suggests []Suggest, max int) (new []Suggest, width int) {
 	return new, leftWidth + rightWidth
 }
 
+// NewCompletionManager returns initialized CompletionManager object.
 func NewCompletionManager(completer Completer, max uint16) *CompletionManager {
 	return &CompletionManager{
 		selected:  -1,
diff --git a/key.go b/key.go
index a6b56ce..9f79185 100644
--- a/key.go
+++ b/key.go
@@ -1,6 +1,9 @@
 package prompt
 
+// Key is the type express the key inserted from user.
 type Key int
+
+// ASCIICode is the type contains Key and it's ascii byte array.
 type ASCIICode struct {
 	Key       Key
 	ASCIICode []byte
diff --git a/prompt.go b/prompt.go
index 5e9a497..148da4b 100644
--- a/prompt.go
+++ b/prompt.go
@@ -14,9 +14,13 @@ const (
 	envEnableLog = "GO_PROMPT_ENABLE_LOG"
 )
 
+// Executor is called when user input something text.
 type Executor func(string)
+
+// Completer should return the suggest item from Document.
 type Completer func(Document) []Suggest
 
+// Prompt is core struct of go-prompt.
 type Prompt struct {
 	in          ConsoleParser
 	buf         *Buffer
@@ -28,10 +32,12 @@ type Prompt struct {
 	keyBindMode KeyBindMode
 }
 
+// Exec is the struct contains user input context.
 type Exec struct {
 	input string
 }
 
+// Run starts prompt.
 func (p *Prompt) Run() {
 	// Logging
 	if os.Getenv(envEnableLog) != "true" {
@@ -187,6 +193,7 @@ func (p *Prompt) feed(b []byte) (shouldExit bool, exec *Exec) {
 	return
 }
 
+// Input just returns user input text.
 func (p *Prompt) Input() string {
 	// Logging
 	if os.Getenv(envEnableLog) != "true" {
diff --git a/render.go b/render.go
index 333c028..ce0eef2 100644
--- a/render.go
+++ b/render.go
@@ -1,5 +1,6 @@
 package prompt
 
+// Render to render prompt information from state of Buffer.
 type Render struct {
 	out    ConsoleWriter
 	prefix string
@@ -23,6 +24,7 @@ type Render struct {
 	selectedDescriptionBGColor   Color
 }
 
+// Setup to initialize console output.
 func (r *Render) Setup() {
 	if r.title != "" {
 		r.out.SetTitle(r.title)
@@ -36,6 +38,7 @@ func (r *Render) renderPrefix() {
 	r.out.SetColor(DefaultColor, DefaultColor, false)
 }
 
+// TearDown to clear title and erasing.
 func (r *Render) TearDown() {
 	r.out.ClearTitle()
 	r.out.EraseDown()
@@ -52,6 +55,7 @@ func (r *Render) prepareArea(lines int) {
 	return
 }
 
+// UpdateWinSize called when window size is changed.
 func (r *Render) UpdateWinSize(ws *WinSize) {
 	r.row = ws.Row
 	r.col = ws.Col
@@ -124,6 +128,7 @@ func (r *Render) renderCompletion(buf *Buffer, completions *CompletionManager) {
 	return
 }
 
+// Render renders to the console.
 func (r *Render) Render(buffer *Buffer, completion *CompletionManager) {
 	// Erasing
 	r.out.CursorBackward(int(r.col) + len(buffer.Text()) + len(r.prefix))
@@ -154,6 +159,7 @@ func (r *Render) Render(buffer *Buffer, completion *CompletionManager) {
 	r.out.Flush()
 }
 
+// BreakLine to break line.
 func (r *Render) BreakLine(buffer *Buffer) {
 	// CR
 	r.out.CursorBackward(int(r.col) + len(buffer.Text()) + len(r.prefix))