diff --git a/infrastructure/fs/swampfile/repository.go b/infrastructure/fs/swampfile/repository.go
index 4d0e3d9..b26bf93 100644
--- a/infrastructure/fs/swampfile/repository.go
+++ b/infrastructure/fs/swampfile/repository.go
@@ -5,8 +5,11 @@ import (
 	"os"
 	"path"
 	"time"
+	"errors"
 )
 
+var ErrDirtyRepo = errors.New("Dirty repository without flag")
+
 type FileSystemSwampFileData struct {
 	path     string
 	size     int64
@@ -46,6 +49,34 @@ type Repository struct {
 	Root string
 }
 
+func NewRepository(root string) (*Repository, error) {
+	fi, err := os.ReadDir(root)
+
+	if err != nil {
+		return nil, err
+	}
+
+	flagpath := path.Join(root, ".bogrepo")
+
+	if len(fi) == 0 {
+		// New Repository, write flagfile
+			f, err := os.OpenFile(flagpath, os.O_CREATE, 0644)
+		if err != nil {
+			return nil, err
+		}
+		f.Close()
+	}
+
+	flagfile, err := os.OpenFile(flagpath, os.O_RDONLY, 0)
+
+	if err != nil {
+		return nil, ErrDirtyRepo
+	}
+	flagfile.Close()
+	return &Repository { root }, nil
+}
+
+
 func (f Repository) absPath(filename string, namespace_ns string) string {
 	return path.Join(f.Root, namespace_ns, filename)
 }
diff --git a/infrastructure/fs/swampfile/repository_test.go b/infrastructure/fs/swampfile/repository_test.go
index e658f7f..6c1102c 100644
--- a/infrastructure/fs/swampfile/repository_test.go
+++ b/infrastructure/fs/swampfile/repository_test.go
@@ -3,17 +3,73 @@ package swampfile
 import (
 	"caj-larsson/bog/dataswamp/swampfile"
 	"path"
+	"os"
 	"testing"
+	"github.com/matryer/is"
 )
 
+func newRepoDir(t *testing.T) string {
+	r := t.TempDir()
+	d := path.Join(r, "fs")
+
+	err := os.Mkdir(d, 0755)
+	if err != nil {
+		panic(err)
+	}
+	return d
+}
+
+
 func TestFsFileRepo(t *testing.T) {
 
 	var fac = func() swampfile.Repository {
-		r := t.TempDir()
-		d := path.Join(r, "fs")
-		repo := Repository{d}
-		return &repo
+		repo, err := NewRepository(newRepoDir(t))
+
+		if err != nil {
+			panic(err)
+		}
+		return repo
 	}
 
 	swampfile.RepositoryContract(fac, t)
 }
+
+
+func TestEmptyDir(t *testing.T) {
+	is := is.New(t)
+	dir_path := newRepoDir(t)
+	_, err := NewRepository(dir_path)
+
+	is.NoErr(err)
+
+	_, err = os.OpenFile(path.Join(dir_path, ".bogrepo"), os.O_RDONLY, 0)
+	is.NoErr(err)
+}
+
+
+func TestDirtyDir(t *testing.T) {
+	is := is.New(t)
+	dir_path := newRepoDir(t)
+
+	_, err := os.OpenFile(path.Join(dir_path, "randomfile"), os.O_CREATE, 0644)
+	is.NoErr(err)
+
+	_, err = NewRepository(dir_path)
+
+	is.Equal(err, ErrDirtyRepo)
+}
+
+
+func TestDirtyWithFlag(t *testing.T) {
+	is := is.New(t)
+	dir_path := newRepoDir(t)
+
+	_, err := os.OpenFile(path.Join(dir_path, "randomfile"), os.O_CREATE, 0644)
+	is.NoErr(err)
+
+	_, err = os.OpenFile(path.Join(dir_path, ".bogrepo"), os.O_CREATE, 0644)
+	is.NoErr(err)
+
+	_, err = NewRepository(dir_path)
+	is.NoErr(err)
+}
diff --git a/server/bog.go b/server/bog.go
index dfddca8..3f65a57 100644
--- a/server/bog.go
+++ b/server/bog.go
@@ -24,9 +24,11 @@ type Bog struct {
 }
 
 func buildFileDataRepository(config FileConfig) swampfile.Repository {
-	fsSwampfileRepo := new(fs_swampfile.Repository)
-	fsSwampfileRepo.Root = config.Path
-	return fsSwampfileRepo
+	r, err := fs_swampfile.NewRepository(config.Path)
+	if err != nil {
+		panic(err)
+	}
+	return r
 }
 
 func buildUserAgentRepository(config DatabaseConfig) namespace.Repository {