diff --git a/cli.go b/cli.go
new file mode 100644
index 0000000..d1bbe28
--- /dev/null
+++ b/cli.go
@@ -0,0 +1,41 @@
+package gitsemvers
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"github.com/jessevdk/go-flags"
+)
+
+const (
+	exitcodeOK = iota
+	exitCodeParseFlagErr
+	exitCodeErr
+)
+
+// CLI is for command line
+type CLI struct {
+	OutStream, ErrStream io.Writer
+}
+
+// Run the cli
+func (cli *CLI) Run(argv []string) int {
+	p, sv, err := parseArgs(argv)
+	if err != nil {
+		if ferr, ok := err.(*flags.Error); !ok || ferr.Type != flags.ErrHelp {
+			p.WriteHelp(cli.ErrStream)
+		}
+		return exitCodeParseFlagErr
+	}
+	fmt.Fprintln(cli.OutStream, strings.Join(sv.VersionStrings(), "\n"))
+	return exitcodeOK
+}
+
+func parseArgs(args []string) (*flags.Parser, *Semvers, error) {
+	sv := &Semvers{}
+	p := flags.NewParser(sv, flags.Default)
+	p.Usage = "[OPTIONS]\n\nVersion: " + version
+	_, err := p.ParseArgs(args)
+	return p, sv, err
+}
diff --git a/cmd/git-semvers/git-semvers.go b/cmd/git-semvers/git-semvers.go
new file mode 100644
index 0000000..cd5efd8
--- /dev/null
+++ b/cmd/git-semvers/git-semvers.go
@@ -0,0 +1,11 @@
+package main
+
+import (
+	"os"
+
+	"github.com/Songmu/gitsemvers"
+)
+
+func main() {
+	os.Exit((&gitsemvers.CLI{ErrStream: os.Stderr, OutStream: os.Stdout}).Run(os.Args[1:]))
+}
diff --git a/gitsemvers.go b/gitsemvers.go
new file mode 100644
index 0000000..3762dc0
--- /dev/null
+++ b/gitsemvers.go
@@ -0,0 +1,117 @@
+package gitsemvers
+
+import (
+	"bytes"
+	"os"
+	"os/exec"
+	"regexp"
+	"sort"
+	"strings"
+
+	"github.com/Masterminds/semver"
+)
+
+const version = "0.0.0"
+
+var verRegStr = `^v?[0-9]+(?:\.[0-9]+){0,2}`
+var extension = `[-0-9A-Za-z]+(?:\.[-0-9A-Za-z]+)*`
+var withPreReleaseRegStr = "(?:-" + extension + ")?"
+var withBuildMetadataRegStr = `(?:\+` + extension + ")?"
+
+type regBuilder uint
+
+const (
+	naked regBuilder = 0
+
+	withPreRelease = 1 << (iota - 1)
+	withBuildMetadata
+
+	withPreReleaseAndBuildMetadata = withPreRelease | withBuildMetadata
+)
+
+var cache = make(map[regBuilder]*regexp.Regexp)
+
+func (rb regBuilder) build() string {
+	b := bytes.NewBufferString(verRegStr)
+	if rb&withPreRelease != 0 {
+		b.WriteString(withPreReleaseRegStr)
+	}
+	if rb&withBuildMetadata != 0 {
+		b.WriteString(withBuildMetadataRegStr)
+	}
+	b.WriteString("$")
+	return b.String()
+}
+
+func (rb regBuilder) reg() *regexp.Regexp {
+	return cache[rb]
+}
+
+func init() {
+	regs := []regBuilder{naked, withPreRelease, withBuildMetadata, withPreReleaseAndBuildMetadata}
+	for _, v := range regs {
+		cache[v] = regexp.MustCompile(v.build())
+	}
+}
+
+// Semvers retrieve semvers from git tags
+type Semvers struct {
+	RepoPath          string `short:"r" long:"repo" default:"." description:"git repository path"`
+	GitPath           string `short:"g" long:"git" default:"git" description:"git path"`
+	WithPreRelease    bool   `short:"P" long:"with-pre-release" description:"display pre-release versions"`
+	WithBuildMetadata bool   `short:"B" long:"with-build-metadata" description:"display build-metadata versions"`
+}
+
+// VersionStrings returns version strings
+func (sv *Semvers) VersionStrings() []string {
+	tags, err := sv.gitTags()
+	if err != nil {
+		return nil
+	}
+	return sv.parseVersions(tags)
+}
+
+func (sv *Semvers) reg() *regexp.Regexp {
+	regB := regBuilder(0)
+	if sv.WithPreRelease {
+		regB |= withPreRelease
+	}
+	if sv.WithBuildMetadata {
+		regB |= withBuildMetadata
+	}
+	return regB.reg()
+}
+
+func (sv *Semvers) gitProg() string {
+	if sv.GitPath != "" {
+		return sv.GitPath
+	}
+	return "git"
+}
+
+func (sv *Semvers) gitTags() (string, error) {
+	cmd := exec.Command(sv.gitProg(), "-C", sv.RepoPath, "tag")
+	var b bytes.Buffer
+	cmd.Stdout = &b
+	cmd.Stderr = os.Stderr
+	err := cmd.Run()
+	return b.String(), err
+}
+
+func (sv *Semvers) parseVersions(out string) []string {
+	rawTags := strings.Split(out, "\n")
+	var versions []*semver.Version
+	for _, tag := range rawTags {
+		t := strings.TrimSpace(tag)
+		if sv.reg().MatchString(t) {
+			v, _ := semver.NewVersion(t)
+			versions = append(versions, v)
+		}
+	}
+	sort.Sort(sort.Reverse(semver.Collection(versions)))
+	var vers = make([]string, len(versions))
+	for i, v := range versions {
+		vers[i] = v.Original()
+	}
+	return vers
+}
diff --git a/gitsemvers_test.go b/gitsemvers_test.go
new file mode 100644
index 0000000..5dcead3
--- /dev/null
+++ b/gitsemvers_test.go
@@ -0,0 +1,74 @@
+package gitsemvers
+
+import (
+	"reflect"
+	"testing"
+)
+
+var input = `dummy
+v0.10.1
+v0.9.0
+v0.9.3
+v0.8.4-pre
+v0.8.4
+v0.8.3+win
+v0.8.2-pre.pre+win.win
+v0.7.0-pre+win+invalid
+`
+
+func TestParseVersions(t *testing.T) {
+	expect := []string{
+		"v0.10.1",
+		"v0.9.3",
+		"v0.9.0",
+		"v0.8.4",
+	}
+	sv := &Semvers{}
+	if !reflect.DeepEqual(sv.parseVersions(input), expect) {
+		t.Errorf("something went wrong %+v", sv.parseVersions(input))
+	}
+}
+
+func TestParseVersionsWithPreRelease(t *testing.T) {
+	expect := []string{
+		"v0.10.1",
+		"v0.9.3",
+		"v0.9.0",
+		"v0.8.4",
+		"v0.8.4-pre",
+	}
+	sv := &Semvers{WithPreRelease: true}
+	if !reflect.DeepEqual(sv.parseVersions(input), expect) {
+		t.Errorf("something went wrong %+v", sv.parseVersions(input))
+	}
+}
+
+func TestParseVersionsWithBuildMetadata(t *testing.T) {
+	expect := []string{
+		"v0.10.1",
+		"v0.9.3",
+		"v0.9.0",
+		"v0.8.4",
+		"v0.8.3+win",
+	}
+	sv := &Semvers{WithBuildMetadata: true}
+	if !reflect.DeepEqual(sv.parseVersions(input), expect) {
+		t.Errorf("something went wrong %+v", sv.parseVersions(input))
+	}
+}
+
+func TestParseVersionsWithAllExtensions(t *testing.T) {
+	expect := []string{
+		"v0.10.1",
+		"v0.9.3",
+		"v0.9.0",
+		"v0.8.4",
+		"v0.8.4-pre",
+		"v0.8.3+win",
+		"v0.8.2-pre.pre+win.win",
+	}
+	sv := &Semvers{WithPreRelease: true, WithBuildMetadata: true}
+	if !reflect.DeepEqual(sv.parseVersions(input), expect) {
+		t.Errorf("something went wrong %+v", sv.parseVersions(input))
+	}
+}