diff --git a/.pylintrc b/.pylintrc
index 9958d1b0f8..b2125d824c 100644
--- a/.pylintrc
+++ b/.pylintrc
@@ -6,6 +6,7 @@ ignored-modules=cv2,tesserocr,ocrd.model
 ignore-patterns='.*generateds.*'
 disable =
     fixme,
+    E501,
     trailing-whitespace,
     logging-not-lazy,
     inconsistent-return-statements,
diff --git a/Makefile b/Makefile
index 16614622de..dd17b20264 100644
--- a/Makefile
+++ b/Makefile
@@ -251,3 +251,10 @@ cuda-ldconfig: /etc/ld.so.conf.d/cuda.conf
 pypi: uninstall install
 	for mod in $(BUILD_ORDER);do (cd $$mod; $(PYTHON) setup.py sdist bdist_wheel);done
 	version=`$(FIND_VERSION)`; twine upload ocrd*/dist/ocrd*$$version*{tar.gz,whl}
+
+#
+# Testing METS server
+#
+
+mets-server-start:
+	uvicorn ocrd.mets_server:app --host 0.0.0.0 --reload
diff --git a/ocrd/ocrd/cli/workspace.py b/ocrd/ocrd/cli/workspace.py
index 81be6aa979..ae010d6c33 100644
--- a/ocrd/ocrd/cli/workspace.py
+++ b/ocrd/ocrd/cli/workspace.py
@@ -16,6 +16,7 @@
 import time
 
 import click
+import uvicorn
 
 from ocrd import Resolver, Workspace, WorkspaceValidator, WorkspaceBackupManager
 from ocrd_utils import getLogger, initLogging, pushd_popd, EXT_TO_MIME, safe_filename, parse_json_string_or_file
@@ -32,6 +33,8 @@ def __init__(self, directory, mets_url, mets_basename, automatic_backup):
             self.log.warning(DeprecationWarning('--mets-basename is deprecated. Use --mets/--directory instead.'))
         self.directory, self.mets_url, self.mets_basename = self.resolver.resolve_mets_arguments(directory, mets_url, mets_basename)
         self.automatic_backup = automatic_backup
+        self.server_options = {}
+
 
 pass_workspace = click.make_pass_decorator(WorkspaceCtx)
 
@@ -674,3 +677,28 @@ def workspace_backup_undo(ctx):
     """
     backup_manager = WorkspaceBackupManager(Workspace(ctx.resolver, directory=ctx.directory, mets_basename=ctx.mets_basename, automatic_backup=ctx.automatic_backup))
     backup_manager.undo()
+
+
+# ----------------------------------------------------------------------
+# ocrd workspace serve
+# ----------------------------------------------------------------------
+
+@workspace_cli.group('server')
+@click.option('-h', '--hostname', help="Hostname for the server", default="localhost")
+@click.option('-p', '--port', help="Port for the server", default=8899)
+@click.pass_context
+def workspace_serve_cli(ctx, hostname, port): # pylint: disable=unused-argument
+    ctx.obj.server_options['hostname'] = hostname
+    ctx.obj.server_options['port'] = port
+
+@workspace_serve_cli.command('start')
+@pass_workspace
+def workspace_serve_start(ctx): # pylint: disable=unused-argument
+    """
+    Start a METS server
+    """
+    workspace_server = WorkspaceServer(
+        workspace=Workspace(ctx.resolver, directory=ctx.directory, mets_basename=ctx.mets_basename),
+        hostname=ctx.server_options['hostname'],
+        port=ctx.server_options['port'])
+    )
diff --git a/ocrd/ocrd/mets_server.py b/ocrd/ocrd/mets_server.py
new file mode 100644
index 0000000000..1a85349772
--- /dev/null
+++ b/ocrd/ocrd/mets_server.py
@@ -0,0 +1,185 @@
+import re
+from os import environ
+from typing import Any, Dict, Optional, Union, List
+
+from fastapi import FastAPI, Request, File, Form, UploadFile
+from fastapi.responses import JSONResponse
+from requests import request
+from pydantic import BaseModel, Field, constr, ValidationError
+
+from ocrd import Resolver
+from ocrd_utils import initLogging, getLogger, deprecated_alias
+
+#
+# XXX
+#
+initLogging()
+workspace = Resolver().workspace_from_url('/home/kba/monorepo/assets/data/kant_aufklaerung_1784/data/mets.xml')
+
+#
+# Models
+#
+
+class OcrdFileModel(BaseModel):
+    file_grp : str = Field()
+    file_id : str = Field()
+    mimetype : str = Field()
+    page_id : Union[str, None] = Field()
+    url : str = Field()
+
+class OcrdFileListModel(BaseModel):
+    files : List[OcrdFileModel] = Field()
+
+#
+# Client
+#
+
+class ClientSideOcrdFile:
+
+    def __init__(self, el, mimetype=None, pageId=None, loctype='OTHER', local_filename=None, mets=None, url=None, ID=None):
+        """
+        Args:
+            el (): ignored
+        Keyword Args:
+            mets (): ignored
+            mimetype (string): ``@MIMETYPE`` of this ``mets:file``
+            pageId (string): ``@ID`` of the physical ``mets:structMap`` entry corresponding to this ``mets:file``
+            loctype (string): ``@LOCTYPE`` of this ``mets:file``
+            local_filename (): ignored
+            url (string): ``@xlink:href`` of this ``mets:file``
+            ID (string): ``@ID`` of this ``mets:file``
+        """
+        self.ID = ID
+        self.mimetype = mimetype
+        self.url = url
+        self.loctype = loctype
+        self.pageId = pageId
+
+class OcrdWorkspaceClient():
+
+    def __init__(self, hostname, port):
+        self.log = getLogger('ocrd.workspace_client')
+        self.url = f'http://{hostname}:{port}'
+
+    def find_files(self, **kwargs):
+        r = request('GET', self.url, params={**kwargs})
+        for f in r.json()['files']:
+            yield ClientSideOcrdFile(None, ID=f.file_id, pageId=f.page_id, fileGrp=f.file_grp, url=f.url)
+
+    def find_all_files(self, *args, **kwargs):
+        return list(self.find_files(*args, **kwargs))
+
+    @deprecated_alias(pageId="page_id")
+    @deprecated_alias(ID="file_id")
+    def add_file(self, file_grp, content=None, file_id=None, url=None, mimetype=None, page_id=None, **kwargs):
+        r = request(
+            'POST',
+            self.url,
+            data=OcrdFileModel(
+                file_id=file_id,
+                file_grp=file_grp,
+                page_id=page_id,
+                mimetype=mimetype,
+                url=url).json(),
+            files=('data', content)
+        )
+
+#
+# FastAPI
+#
+
+app = FastAPI(
+    title="OCR-D Workspace Server",
+    description="Providing simultaneous write-access to mets.xml for OCR-D",
+)
+
+@app.exception_handler(ValidationError)
+async def exception_handler_invalid400(request: Request, exc: ValidationError):
+    return JSONResponse(status_code=400, content=exc.errors())
+
+@app.exception_handler(FileExistsError)
+async def exception_handler_invalid400(request: Request, exc: FileExistsError):
+    return JSONResponse(status_code=400, content=str(exc))
+
+@app.exception_handler(re.error)
+async def exception_handler_invalid400(request: Request, exc: re.error):
+    return JSONResponse(status_code=400, content=f'invalid regex: {exc}')
+
+@app.on_event("startup")
+async def on_startup():
+    getLogger('ocrd.mets_server').info("Starting up")
+
+
+@app.on_event("shutdown")
+async def on_shutdown():
+    getLogger('ocrd.mets_server').info("Shutting down")
+
+@app.get(
+    "/",
+    # response_model=OcrdFileListModel,
+)
+async def find_files(
+    file_grp : Union[str, None] = None,
+    file_id : Union[str, None] = None,
+    page_id : Union[str, None] = None,
+    mimetype : Union[str, None] = None,
+    ):
+    """
+    Find files in the mets
+    """
+    found = workspace.mets.find_all_files(fileGrp=file_grp, ID=file_id, pageId=page_id, mimetype=mimetype)
+    return OcrdFileListModel(
+        files=[OcrdFileModel(file_grp=of.fileGrp, file_id=of.ID, mimetype=of.mimetype, page_id=of.pageId, url=of.url) for of in found]
+    )
+
+@app.delete('/')
+async def stop():
+    """
+    Stop the server
+    """
+    # TODO
+
+@app.post(
+    '/',
+    response_model=OcrdFileModel
+)
+async def add_file(
+    data : bytes = File(),
+    file_grp : str = Form(),
+    file_id : str = Form(),
+    page_id : Union[str, None] = Form(),
+    mimetype : str = Form(),
+    url : str = Form(),
+):
+    """
+    Add a file
+    """
+    # Validate
+    file_resource = OcrdFileModel(file_grp=file_grp, file_id=file_id, page_id=page_id, mimetype=mimetype, url=url)
+    # Add to workspace
+    kwargs = file_resource.dict()
+    kwargs['page_id'] = page_id
+    kwargs['content'] = data
+    kwargs['local_filename'] = kwargs.pop('url')
+    workspace.add_file(**kwargs)
+    workspace.save_mets()
+    return file_resource
+
+#
+# Server
+#
+
+class OcrdWorkspaceServer():
+
+    def __init__(self):
+        self.hostname = hostname
+        self.port = port
+        self.log = getLogger('ocrd.workspace_client')
+
+    def shutdown():
+        pass
+
+    def startup():
+        uvicorn.run(workspace_server.app, hostname=self.hostname, port=self.port)
+
+
diff --git a/ocrd/requirements.txt b/ocrd/requirements.txt
index ad30bc1f83..7fe49d1924 100644
--- a/ocrd/requirements.txt
+++ b/ocrd/requirements.txt
@@ -10,3 +10,6 @@ pyyaml
 Deprecated == 1.2.0
 memory-profiler >= 0.58.0
 sparklines >= 0.4.2
+uvicorn
+fastapi
+python-multipart
diff --git a/repo/spec b/repo/spec
index 02b6233d31..a859ada2d2 160000
--- a/repo/spec
+++ b/repo/spec
@@ -1 +1 @@
-Subproject commit 02b6233d316a0125286b878f953fcd2c59228d39
+Subproject commit a859ada2d22a2888949ab786a108c76c5aa2e017