diff --git a/TODO.txt b/TODO.txt
index 66a713c..de59588 100644
--- a/TODO.txt
+++ b/TODO.txt
@@ -1,3 +1,2 @@
 * add disk quota
 * add LRU cache
-* add offline mode
diff --git a/pkg/fs/file.go b/pkg/fs/file.go
index ac39d0f..907c4ac 100644
--- a/pkg/fs/file.go
+++ b/pkg/fs/file.go
@@ -3,6 +3,7 @@
 package fs
 
 import (
+	"errors"
 	"io"
 	"os"
 
@@ -10,10 +11,11 @@ import (
 )
 
 type File struct {
-	log    logr.Logger
-	f      *os.File
-	md     *Metadata
-	offset int64
+	log     logr.Logger
+	f       *os.File
+	md      *Metadata
+	offset  int64
+	offline bool
 }
 
 type preload struct {
@@ -38,23 +40,34 @@ func (p *preload) Read(data []byte) (n int, err error) {
 }
 
 func (f *File) Preload(unlock func()) {
-	f.log.V(2).Info("preload started")
+	log := f.log
+	if f.offline {
+		log.V(2).Error(errors.New("no preload in offline mode"), "error preloading file")
+		unlock()
+		return
+	}
+	log.V(2).Info("preload started")
 	p := &preload{f: f}
 	_, err := io.Copy(io.Discard, p)
 	if err != nil && err != io.EOF {
-		f.log.Error(err, "error preloading file")
+		log.Error(err, "error preloading file")
 	}
-	f.log.V(2).Info("preload finished", "skipped", p.skipped, "written", p.written)
+	log.V(2).Info("preload finished", "skipped", p.skipped, "written", p.written)
 	unlock()
 }
 
 func (f *File) Read(p []byte) (n int, err error) {
+	log := f.log
 	if f.hasChunk(len(p)) {
 		n, err = f.md.ReadAt(p, f.offset)
 		if err != nil {
+			log.Error(err, "error reading cache file")
 			return
 		}
 		_, err = f.Seek(int64(n), io.SeekCurrent)
+		if err != nil {
+			log.Error(err, "error seeking source file")
+		}
 		return
 	}
 	return f.readWithoutCache(p)
@@ -69,8 +82,12 @@ func (f *File) hasChunk(n int) bool {
 }
 
 func (f *File) readWithoutCache(p []byte) (n int, err error) {
+	if f.offline {
+		return 0, io.EOF
+	}
 	n, err = f.f.Read(p)
 	if err != nil {
+		f.log.Error(err, "error reading source file")
 		return
 	}
 	f.md.WriteAt(p, f.offset)
@@ -82,6 +99,7 @@ func (f *File) readWithoutCache(p []byte) (n int, err error) {
 func (f *File) Seek(offset int64, whence int) (n int64, err error) {
 	n, err = f.f.Seek(offset, whence)
 	if err != nil {
+		f.log.Error(err, "error seeking source file")
 		return
 	}
 	switch whence {
diff --git a/pkg/fs/fs.go b/pkg/fs/fs.go
index b650cc8..932ca2d 100644
--- a/pkg/fs/fs.go
+++ b/pkg/fs/fs.go
@@ -73,16 +73,27 @@ func NewFS(src, dst, metadata string, log logr.Logger) (fs *FS, err error) {
 	return fs, err
 }
 
-func (fs *FS) Stat(name string) (stdfs.FileInfo, error) {
-	return stat(fs.src, name)
+func (fs *FS) Stat(name string) (fi stdfs.FileInfo, err error) {
+	fi, _, err = fs.StatWithOffline(name)
+	return
+}
+
+func (fs *FS) StatWithOffline(name string) (fi stdfs.FileInfo, offline bool, err error) {
+	f, err := fs.open(name, true)
+	if err != nil {
+		return
+	}
+	fi, err = f.Stat()
+	offline = f.offline
+	return
 }
 
 func (fs *FS) Open(name string) (http.File, error) {
-	return fs.open(name)
+	return fs.open(name, false)
 }
 
 func (fs *FS) Preload(name string) {
-	f, err := fs.open(name)
+	f, err := fs.open(name, false)
 	if err != nil {
 		return
 	}
@@ -95,66 +106,82 @@ func (fs *FS) Preload(name string) {
 }
 
 func skipLog(name string) bool {
-	return strings.HasSuffix(name, "index.html")
+	return strings.HasSuffix(name, "index.html") || strings.HasSuffix(name, "favicon.ico")
 }
 
-func (fs *FS) open(name string) (f *File, err error) {
+func (fs *FS) open(name string, stat bool) (f *File, err error) {
 	log := fs.log.WithValues("file", name)
-	rp := filepath.Join(fs.src, filepath.FromSlash(path.Clean("/"+name)))
-	rf, err := os.Open(rp)
+	p := filepath.FromSlash(path.Clean("/" + name))
+	sp := filepath.Join(fs.src, p)
+	dp := filepath.Join(fs.dst, p)
+	offline := false
+	sf, err := os.Open(sp)
 	if err != nil {
-		if !skipLog(name) {
-			log.Error(err, "error opening source file")
+		if errors.Is(err, os.ErrNotExist) {
+			sf, err = os.Open(dp)
+			if err != nil {
+				if !skipLog(name) {
+					log.Error(err, "error opening source file")
+				}
+				return
+			}
+			offline = true
+			log.V(2).Info("file offline mode", "path", dp)
 		}
-		return
 	}
-	rfi, err := rf.Stat()
+	sfi, err := sf.Stat()
 	if err != nil {
 		log.Error(err, "error stat source file")
 		return
 	}
-	if rfi.IsDir() {
-		return &File{f: rf}, nil
+	if sfi.IsDir() || stat {
+		if empty, err := dirEmpty(sf.Name()); empty && err == nil {
+			sf, err = os.Open(dp)
+			offline = true
+			log.V(2).Info("dir offline mode", "path", dp)
+		}
+		return &File{f: sf, offline: offline}, err
 	}
-	mp := filepath.Join(fs.dst, filepath.FromSlash(path.Clean("/"+name)))
-	var mf *os.File
-	i := strings.LastIndex(mp, "/")
+	var df *os.File
+	i := strings.LastIndex(dp, "/")
 	if i > 0 {
-		dir := mp[:i]
+		dir := dp[:i]
 		_, err = os.Stat(dir)
 		if errors.Is(err, os.ErrNotExist) {
 			err = os.MkdirAll(dir, 0o755)
 			if err != nil {
-				log.Error(err, "error creating cache dir", "dir", mp)
+				log.Error(err, "error creating cache dir", "dir", dp)
 				return nil, err
 			}
 		}
 	}
-	_, err = os.Stat(mp)
+	_, err = os.Stat(dp)
 	truncate := errors.Is(err, os.ErrNotExist)
 	if !fs.isOpen(name) {
-		mf, err = os.OpenFile(mp, os.O_RDWR|os.O_CREATE, 0o644)
+		df, err = os.OpenFile(dp, os.O_RDWR|os.O_CREATE, 0o644)
 		if err != nil {
 			log.Error(err, "error opening cache file")
 			return nil, err
 		}
 		if truncate {
-			err = mf.Truncate(rfi.Size())
+			err = df.Truncate(sfi.Size())
 			if err != nil {
 				log.Error(err, "error truncating cache file")
 				return nil, err
 			}
-			err = mf.Sync()
+			err = df.Sync()
 			if err != nil {
 				log.Error(err, "error syncing cache file")
 				return nil, err
 			}
 		}
 	}
+	md := fs.metadata(name, sfi.Size(), df)
 	return &File{
-		log: log,
-		f:   rf,
-		md:  fs.metadata(name, rfi.Size(), mf),
+		log:     log,
+		f:       sf,
+		md:      md,
+		offline: offline,
 	}, nil
 }
 
@@ -219,7 +246,21 @@ func (fs *FS) Close() {
 	fs.flushMetadata()
 }
 
-func stat(prefix, name string) (stdfs.FileInfo, error) {
-	p := filepath.Join(prefix, filepath.FromSlash(path.Clean("/"+name)))
-	return os.Stat(p)
+func dirEmpty(name string) (bool, error) {
+	f, err := os.Open(name)
+	if err != nil {
+		return false, err
+	}
+	defer f.Close()
+	_, err = f.Readdir(1)
+	if err == io.EOF {
+		return true, nil
+	}
+	return false, err
+}
+
+func stat(dst, name string) (fi stdfs.FileInfo, err error) {
+	p := filepath.FromSlash(path.Clean("/" + name))
+	dp := filepath.Join(dst, p)
+	return os.Stat(dp)
 }
diff --git a/pkg/srv/srv.go b/pkg/srv/srv.go
index 41c5169..6f80157 100644
--- a/pkg/srv/srv.go
+++ b/pkg/srv/srv.go
@@ -49,7 +49,7 @@ func (fs *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		r.URL.Path = upath
 	}
 	p := path.Clean(upath)
-	d, err := fs.fs.Stat(p)
+	d, offline, err := fs.fs.StatWithOffline(p)
 	if err != nil {
 		msg, code := toHTTPError(err)
 		http.Error(w, msg, code)
@@ -82,7 +82,16 @@ func (fs *FileServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	i := &responseInterceptor{w: w}
+	// TODO implement directory listing cache
+	offline = true
+	if offline {
+		r.Header.Del("If-Modified-Since")
+		r.Header.Del("Cache-Control")
+	}
 	fs.h.ServeHTTP(i, r)
+	if offline {
+		w.Header().Del("Last-Modified")
+	}
 	paths, err := i.GetPaths()
 	if err == io.EOF {
 		w.WriteHeader(i.Status())