diff --git a/cmd/chatlog/cmd_server.go b/cmd/chatlog/cmd_server.go
index c606f62..9d377fe 100644
--- a/cmd/chatlog/cmd_server.go
+++ b/cmd/chatlog/cmd_server.go
@@ -36,6 +36,8 @@ var serverCmd = &cobra.Command{
 	Use:   "server",
 	Short: "Start HTTP server",
 	Run: func(cmd *cobra.Command, args []string) {
+		cleanup := initSingleInstance()
+		defer cleanup()
 
 		cmdConf := getServerConfig()
 		log.Info().Msgf("server cmd config: %+v", cmdConf)
diff --git a/cmd/chatlog/root.go b/cmd/chatlog/root.go
index da88bcb..e45f5ce 100644
--- a/cmd/chatlog/root.go
+++ b/cmd/chatlog/root.go
@@ -1,7 +1,12 @@
 package chatlog
 
 import (
+	"fmt"
+	"os"
+
 	"github.com/sjzar/chatlog/internal/chatlog"
+	"github.com/sjzar/chatlog/pkg/process"
+	"github.com/sjzar/chatlog/pkg/util"
 
 	"github.com/rs/zerolog/log"
 	"github.com/spf13/cobra"
@@ -35,8 +40,20 @@ var rootCmd = &cobra.Command{
 }
 
 func Root(cmd *cobra.Command, args []string) {
+	cleanup := initSingleInstance()
+	defer cleanup()
+
 	m := chatlog.New()
 	if err := m.Run(""); err != nil {
 		log.Err(err).Msg("failed to run chatlog instance")
 	}
 }
+
+func initSingleInstance() func() {
+	cleanup, err := process.CheckSingleInstance(util.DefaultWorkDir(""))
+	if err != nil {
+		fmt.Fprintln(os.Stderr, "Error:", err)
+		os.Exit(1)
+	}
+	return cleanup
+}
diff --git a/pkg/process/process.go b/pkg/process/process.go
new file mode 100644
index 0000000..b04805e
--- /dev/null
+++ b/pkg/process/process.go
@@ -0,0 +1,65 @@
+package process
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+
+	"github.com/shirou/gopsutil/v4/process"
+)
+
+// CheckSingleInstance checks if another instance is running using a PID file.
+// If another instance is found, it prompts the user to force close it.
+// Returns a cleanup function to be called on exit.
+func CheckSingleInstance(workDir string) (func(), error) {
+	pidFile := filepath.Join(workDir, "chatlog.pid")
+
+	// Read existing PID file
+	if content, err := os.ReadFile(pidFile); err == nil {
+		pidStr := strings.TrimSpace(string(content))
+		if pid, err := strconv.Atoi(pidStr); err == nil {
+			// Check if process exists
+			if exists, _ := process.PidExists(int32(pid)); exists {
+				// Process exists, check if it's really us (optional, but good practice)
+				// For now, just assume if PID exists it might be us or a zombie.
+				// We can check process name if needed, but pid file is strong hint.
+				
+				fmt.Printf("Detected another instance running (PID: %d).\n", pid)
+				fmt.Print("Do you want to force close it and continue? [y/N]: ")
+				
+				reader := bufio.NewReader(os.Stdin)
+				input, _ := reader.ReadString('\n')
+				input = strings.TrimSpace(strings.ToLower(input))
+
+				if input == "y" || input == "yes" {
+					if p, err := process.NewProcess(int32(pid)); err == nil {
+						if err := p.Kill(); err != nil {
+							return nil, fmt.Errorf("failed to kill process: %w", err)
+						}
+						fmt.Println("Process killed.")
+					} else {
+						// Process might have exited in the meantime
+						fmt.Println("Process not found, continuing...")
+					}
+				} else {
+					return nil, fmt.Errorf("application already running")
+				}
+			}
+		}
+	}
+
+	// Write current PID
+	currentPID := os.Getpid()
+	if err := os.WriteFile(pidFile, []byte(strconv.Itoa(currentPID)), 0644); err != nil {
+		return nil, fmt.Errorf("failed to write pid file: %w", err)
+	}
+
+	// Cleanup function
+	return func() {
+		os.Remove(pidFile)
+	},
+	nil
+}