diff --git a/cista/app.py b/cista/app.py
index b2e28a9..7e7c098 100755
--- a/cista/app.py
+++ b/cista/app.py
@@ -1,21 +1,54 @@
+import asyncio
 from importlib.resources import files
 
 import msgspec
 from html5tagger import E
-from sanic import Sanic, redirect
+from sanic import Forbidden, Sanic, SanicException, errorpages
 from sanic.log import logger
-from sanic.response import html
+from sanic.response import html, json, redirect
 
 from . import config, session, watching
 from .auth import authbp
 from .fileio import FileServer
-from .protocol import ErrorMsg, FileRange, StatusMsg
+from .protocol import ControlBase, ErrorMsg, FileRange, StatusMsg
+
 
 app = Sanic("cista")
 fileserver = FileServer()
 watching.register(app, "/api/watch")
 app.blueprint(authbp)
 
+@app.on_request
+async def use_session(request):
+    request.ctx.session = session.get(request)
+    # CSRF protection
+    if request.method == "GET" and request.headers.upgrade != "websocket":
+        return  # Ordinary GET requests are fine
+    if request.headers.origin.split("//", 1)[1] != request.host:
+        raise Forbidden("Invalid origin: Cross-Site requests not permitted")
+
+@app.exception(Exception)
+async def handle_sanic_exception(request, e):
+    context, code, message = {}, 500, str(e) or "Internal Server Error"
+    if isinstance(e, SanicException):
+        context = e.context or {}
+        code = e.status_code
+    message = f"⚠️ {message}"
+    # Non-browsers get JSON errors
+    if "text/html" not in request.headers.accept:
+        return json({"error": {"code": code, "message": message, **context}}, status=code)
+    # Redirections flash the error message via cookies
+    if "redirect" in context:
+        res = redirect(context["redirect"])
+        res.cookies.add_cookie("message", message, max_age=5)
+        return res
+    # Otherwise use Sanic's default error page
+    return errorpages.HTMLRenderer(request, e, debug=app.debug).full()
+
+@app.on_response
+async def resphandler(request, response):
+    print("In response handler", request.path, response)
+
 def asend(ws, msg):
     return ws.send(msg if isinstance(msg, bytes) else msgspec.json.encode(msg).decode())
 
@@ -36,11 +69,11 @@ async def index_page(request):
     if not s:
         return redirect("/login")
     index = files("cista").joinpath("static", "index.html").read_text()
-    flash = request.cookies.flash
+    flash = request.cookies.message
     if flash:
-        index += str(E.div(flash, id="flash"))
+        index += str(E.dialog(flash, id="flash", open=True, style="position: fixed; top: 0; left: 0; width: 100%; opacity: .8"))
         res = html(index)
-        res.cookies.delete_cookie("flash")
+        session.flash(res, None)
         return res
     return html(index)
 
@@ -101,3 +134,9 @@ async def download(request, ws):
             await asend(ws, res)
             logger.exception(repr(res), e)
             return
+
+@app.websocket("/api/control")
+async def control(request, websocket):
+    cmd = msgspec.json.decode(await websocket.recv(), type=ControlBase)
+    await asyncio.to_thread(cmd)
+    await asend(websocket, StatusMsg(status="ack", req=cmd))
diff --git a/cista/auth.py b/cista/auth.py
index 32faca8..64538b8 100755
--- a/cista/auth.py
+++ b/cista/auth.py
@@ -6,7 +6,7 @@ from unicodedata import normalize
 import argon2
 import msgspec
 from html5tagger import Document
-from sanic import BadRequest, Blueprint, html, json, redirect
+from sanic import BadRequest, Blueprint, Forbidden, html, json, redirect
 
 from . import config, session
 
@@ -64,18 +64,17 @@ async def login_page(request):
     with doc.div(id="login"):
         with doc.form(method="POST", autocomplete="on"):
             doc.h1("Login")
-            doc.input(name="username", placeholder="Username", autocomplete="username").br
-            doc.input(type="password", name="password", placeholder="Password", autocomplete="current-password").br
+            doc.input(name="username", placeholder="Username", autocomplete="username", required=True).br
+            doc.input(type="password", name="password", placeholder="Password", autocomplete="current-password", required=True).br
             doc.input(type="submit", value="Login")
         s = session.get(request)
         if s:
             name = s["username"]
             with doc.form(method="POST", action="/logout"):
                 doc.input(type="submit", value=f"Logout {name}")
-    flash = request.cookies.flash
+    flash = request.cookies.message
     if flash:
-        print("flash", flash)
-        doc.p(flash)
+        doc.dialog(flash, id="flash", open=True, style="position: fixed; top: 0; left: 0; width: 100%; opacity: .8")
     res = html(doc)
     if flash:
         res.cookies.delete_cookie("flash")
@@ -85,9 +84,8 @@ async def login_page(request):
 
 @authbp.post("/login")
 async def login_post(request):
-    json_format = request.headers.content_type == "application/json"
     try:
-        if json_format:
+        if request.headers.content_type == "application/json":
             username = request.json["username"]
             password = request.json["password"]
         else:
@@ -96,36 +94,28 @@ async def login_post(request):
         if not username or not password:
             raise KeyError
     except KeyError:
-        raise BadRequest("Missing username or password")
+        raise BadRequest("Missing username or password", context={"redirect": "/login"})
     try:
         user = login(username, password)
     except ValueError as e:
-        if json_format:
-            res = json({
-                "status": "error",
-                "error": str(e),
-            })
-        else:
-            res = redirect("/login")
-            res.cookies.add_cookie("flash", str(e), max_age=5)
-            print("Login error:", res.cookies)
-        return res
+        raise Forbidden(str(e), context={"redirect": "/login"})
 
-    if json_format:
-        res = json({
-            "status": "authenticated",
-            "user": username,
-            "privileged": user.privileged,
-        })
-    else:
+    if "text/html" in request.headers.accept:
         res = redirect("/")
-        res.cookies.add_cookie("flash", "Logged in", max_age=5)
+        session.flash(res, "Logged in")
+    else:
+        res = json({"data": {"username": username, "privileged": user.privileged}})
     session.create(res, username)
     return res
 
 @authbp.post("/logout")
 async def logout_post(request):
-    res = redirect("/")
+    s = request.ctx.session
+    msg = "Logged out" if s else "Not logged in"
+    if "text/html" in request.headers.accept:
+        res = redirect("/login")
+        res.cookies.add_cookie("flash", msg, max_age=5)
+    else:
+        res = json({"message": msg})
     session.delete(res)
-    res.cookies.add_cookie("flash", "Logged out", max_age=5)
     return res
diff --git a/cista/fileio.py b/cista/fileio.py
index e225d82..6bedc7e 100755
--- a/cista/fileio.py
+++ b/cista/fileio.py
@@ -5,7 +5,7 @@ from pathlib import Path, PurePosixPath
 
 from pathvalidate import sanitize_filepath
 
-from . import config
+from . import config, protocol
 from .asynclink import AsyncLink
 from .lrucache import LRUCache
 
@@ -80,6 +80,8 @@ class FileServer:
         try:
             for req in slink:
                 with req as (command, *args):
+                    if command == "control":
+                        self.control(*args)
                     if command == "upload":
                         req.set_result(self.upload(*args))
                     elif command == "download":
diff --git a/cista/protocol.py b/cista/protocol.py
index f24966d..494fe8e 100755
--- a/cista/protocol.py
+++ b/cista/protocol.py
@@ -1,9 +1,67 @@
 from __future__ import annotations
+import shutil
 
-from typing import Dict, Tuple, Union
+from sanic import BadRequest
+from cista import config
+from cista.fileio import sanitize_filename
 
 import msgspec
 
+## Control commands
+
+class ControlBase(msgspec.Struct, tag_field="op", tag=str.lower):
+    def __call__(self):
+        raise NotImplementedError
+
+class MkDir(ControlBase):
+    path: str
+    def __call__(self):
+        path = config.config.path / sanitize_filename(self.path)
+        path.mkdir(parents=False, exist_ok=False)
+
+class Rename(ControlBase):
+    path: str
+    to: str
+    def __call__(self):
+        to = sanitize_filename(self.to)
+        if "/" in to:
+            raise BadRequest("Rename 'to' name should only contain filename, not path")
+        path = config.config.path / sanitize_filename(self.path)
+        path.rename(path.with_name(to))
+
+class Rm(ControlBase):
+    sel: list[str]
+    def __call__(self):
+        root = config.config.path
+        sel = [root / sanitize_filename(p) for p in self.sel]
+        for p in sel:
+            shutil.rmtree(p, ignore_errors=True)
+
+class Mv(ControlBase):
+    sel: list[str]
+    dst: str
+    def __call__(self):
+        root = config.config.path
+        sel = [root / sanitize_filename(p) for p in self.sel]
+        dst = root / sanitize_filename(self.dst)
+        if not dst.is_dir():
+            raise BadRequest("The destination must be a directory")
+        for p in sel:
+            shutil.move(p, dst)
+
+class Cp(ControlBase):
+    sel: list[str]
+    dst: str
+    def __call__(self):
+        root = config.config.path
+        sel = [root / sanitize_filename(p) for p in self.sel]
+        dst = root / sanitize_filename(self.dst)
+        if not dst.is_dir():
+            raise BadRequest("The destination must be a directory")
+        for p in sel:
+            # Note: copies as dst rather than in dst unless name is appended.
+            shutil.copytree(p, dst / p.name, dirs_exist_ok=True, ignore_dangling_symlinks=True)
+
 ## File uploads and downloads
 
 class FileRange(msgspec.Struct):
@@ -52,7 +110,7 @@ class DirEntry(msgspec.Struct):
             if k != "dir"
         }
 
-DirList = dict[str, Union[FileEntry, DirEntry]]
+DirList = dict[str, FileEntry | DirEntry]
 
 
 class UpdateEntry(msgspec.Struct, omit_defaults=True):
diff --git a/cista/session.py b/cista/session.py
index a310f0e..7d0bc94 100755
--- a/cista/session.py
+++ b/cista/session.py
@@ -30,3 +30,10 @@ def update(res, s, **kwargs):
 
 def delete(res):
     res.cookies.delete_cookie("s")
+
+
+def flash(res, message: str | None):
+    if message is None:
+        res.cookies.delete_cookie("message")
+    else:
+        res.cookies.add_cookie("message", message, max_age=5)
diff --git a/pyproject.toml b/pyproject.toml
index 1b96717..e163766 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,6 +30,11 @@ Homepage = ""
 [project.scripts]
 cista = "cista.__main__:main"
 
+[project.optional-dependencies]
+dev = [
+    "pytest",
+]
+
 [tool.hatch.version]
 source = "vcs"
 
@@ -43,3 +48,13 @@ version_tuple = {version_tuple!r}
 targets.sdist.include = [
     "/cista",
 ]
+
+[tool.pytest.ini_options]
+addopts = [
+    "--import-mode=importlib",
+    "--verbosity=-1",
+    "-p no:warnings",
+]
+testpaths = [
+    "tests",
+]
diff --git a/tests/test_control.py b/tests/test_control.py
new file mode 100644
index 0000000..bd767a4
--- /dev/null
+++ b/tests/test_control.py
@@ -0,0 +1,45 @@
+import pytest
+from cista import config
+from cista.protocol import MkDir, Rename, Rm, Mv, Cp
+from pathlib import Path
+import tempfile
+
+@pytest.fixture
+def setup_temp_dir():
+    with tempfile.TemporaryDirectory() as tmpdirname:
+        config.config = config.Config(path=Path(tmpdirname), listen=":0")
+        yield Path(tmpdirname)
+
+def test_mkdir(setup_temp_dir):
+    cmd = MkDir(path="new_folder")
+    cmd()
+    assert (setup_temp_dir / "new_folder").is_dir()
+
+def test_rename(setup_temp_dir):
+    (setup_temp_dir / "old_name").mkdir()
+    cmd = Rename(path="old_name", to="new_name")
+    cmd()
+    assert not (setup_temp_dir / "old_name").exists()
+    assert (setup_temp_dir / "new_name").is_dir()
+
+def test_rm(setup_temp_dir):
+    (setup_temp_dir / "folder_to_remove").mkdir()
+    cmd = Rm(sel=["folder_to_remove"])
+    cmd()
+    assert not (setup_temp_dir / "folder_to_remove").exists()
+
+def test_mv(setup_temp_dir):
+    (setup_temp_dir / "folder_to_move").mkdir()
+    (setup_temp_dir / "destination").mkdir()
+    cmd = Mv(sel=["folder_to_move"], dst="destination")
+    cmd()
+    assert not (setup_temp_dir / "folder_to_move").exists()
+    assert (setup_temp_dir / "destination" / "folder_to_move").is_dir()
+
+def test_cp(setup_temp_dir):
+    (setup_temp_dir / "folder_to_copy").mkdir()
+    (setup_temp_dir / "destination").mkdir()
+    cmd = Cp(sel=["folder_to_copy"], dst="destination")
+    cmd()
+    assert (setup_temp_dir / "folder_to_copy").is_dir()
+    assert (setup_temp_dir / "destination" / "folder_to_copy").is_dir()