diff --git a/cmd/slacksend/main.go b/cmd/slacksend/main.go
index f7dc3df..26604ba 100644
--- a/cmd/slacksend/main.go
+++ b/cmd/slacksend/main.go
@@ -1,11 +1,16 @@
 package main
 
-import "fmt"
+import (
+	"os"
+
+	"gitea.pglikers.com/tools/slacksend/internal/cli"
+)
 
 func hello() string {
 	return "hello"
 }
 
+
 func main() {
-	fmt.Println(hello())
-}
\ No newline at end of file
+	os.Exit(cli.Run(os.Args))
+}
diff --git a/go.mod b/go.mod
index 250cc7f..46ed05c 100644
--- a/go.mod
+++ b/go.mod
@@ -1,3 +1,3 @@
-module gitea.pglikers.com/tools/slacksen
+module gitea.pglikers.com/tools/slacksend
 
 go 1.25.5
diff --git a/internal/cli/cli.go b/internal/cli/cli.go
new file mode 100644
index 0000000..d702db4
--- /dev/null
+++ b/internal/cli/cli.go
@@ -0,0 +1,70 @@
+package cli
+
+import (
+	"flag"
+	"fmt"
+	"io"
+	"os"
+	"strings"
+
+	"gitea.pglikers.com/tools/slacksend/internal/version"
+)
+
+type Options struct {
+	ShowVersion bool
+}
+
+func Run(args []string) int {
+	return run(args, os.Stdin, os.Stdout, os.Stderr)
+}
+
+func run(args []string, stdin io.Reader, stdout, stderr io.Writer) int {
+	fs := flag.NewFlagSet("slacksend", flag.ContinueOnError)
+	fs.SetOutput(stderr)
+	fs.Usage = func() { Usage(stdout) }
+
+	var opt Options
+	fs.BoolVar(&opt.ShowVersion, "version", false, "show version")
+	fs.BoolVar(&opt.ShowVersion, "V", false, "show version (short)")
+
+	if err := fs.Parse(args[1:]); err != nil {
+		if err == flag.ErrHelp {
+			Usage(stdout)
+			return 0
+		}
+		fmt.Fprintln(stderr, err)
+		Usage(stderr)
+		return 2
+	}
+
+	if opt.ShowVersion {
+		fmt.Fprintln(stdout, version.String())
+		return 0
+	}
+
+	msg, err := message(fs.Args(), stdin)
+	if err != nil {
+		fmt.Fprintln(stderr, "read message error:", err)
+		return 1
+	}
+	if msg == "" {
+		Usage(stderr)
+		return 2
+	}
+
+	// TODO: Slack送信（ここはあとで internal/slack に逃がす）
+	fmt.Fprintln(stdout, msg)
+	return 0
+}
+
+func message(args []string, stdin io.Reader) (string, error) {
+	if len(args) > 0 {
+		return strings.Join(args, " "), nil
+	}
+	b, err := io.ReadAll(stdin)
+	if err != nil {
+		return "", err
+	}
+	return strings.TrimSpace(string(b)), nil
+}
+
diff --git a/internal/cli/usage.go b/internal/cli/usage.go
new file mode 100644
index 0000000..9a6b89d
--- /dev/null
+++ b/internal/cli/usage.go
@@ -0,0 +1,27 @@
+package cli
+
+import (
+	"fmt"
+	"io"
+)
+
+func Usage(w io.Writer) {
+	fmt.Fprint(w, `slacksend - send a message to Slack (Incoming Webhook)
+
+Usage:
+  slacksend [options] <message...>
+  echo "message" | slacksend [options]
+
+Options:
+  -V, --version             show version
+  -h, --help     show this help
+
+Environment:
+  SLACK_WEBHOOK_URL   Slack Incoming Webhook URL
+
+Examples:
+  export SLACK_WEBHOOK_URL="https://hooks.slack.com/services/XXX/YYY/ZZZ"
+  slacksend "hello slack"
+  echo "hello from stdin" | slacksend
+`)
+}
diff --git a/internal/version/version.go b/internal/version/version.go
new file mode 100644
index 0000000..cb47f30
--- /dev/null
+++ b/internal/version/version.go
@@ -0,0 +1,16 @@
+package version
+
+var (
+	// Version is the application version.
+	Version = "dev"
+
+	// Commit is the git commit hash.
+	Commit = "none"
+
+	// Date is the build date.
+	Date = "unknown"
+)
+
+func String() string {
+	return Version + " (" + Commit + ", " + Date + ")"
+}
\ No newline at end of file