diff --git a/.gitignore b/.gitignore
index 82ec99b6..317d8064 100644
--- a/.gitignore
+++ b/.gitignore
@@ -16,3 +16,4 @@ __pycache__
 .#*
 .coverage
 .cache
+.pytest_cache
diff --git a/jupyterlab_launcher/handlers.py b/jupyterlab_launcher/handlers.py
index 93d0193a..fc70b820 100644
--- a/jupyterlab_launcher/handlers.py
+++ b/jupyterlab_launcher/handlers.py
@@ -142,6 +142,9 @@ class LabConfig(HasTraits):
                                 'schemas directory. If given, a handler will '
                                 'be added for settings.'))
 
+    workspaces_api_url = Unicode(default_workspaces_api_url,
+                                 help='The url path of the workspaces API.')
+
     workspaces_dir = Unicode('',
                              help=('The optional location of the saved '
                                    'workspaces directory. If given, a handler '
@@ -185,11 +188,11 @@ def add_handlers(web_app, config):
 
     # Set up the main page handler and tree handler.
     base_url = web_app.settings['base_url']
-    lab_url = ujoin(base_url, config.page_url)
-    tree_url = ujoin(base_url, config.tree_url + r'.+')
+    lab_path = ujoin(base_url, config.page_url)
+    tree_path = ujoin(base_url, config.tree_url, r'.+')
     handlers = [
-        (lab_url, LabHandler, {'lab_config': config}),
-        (tree_url, LabHandler, {'lab_config': config})
+        (lab_path, LabHandler, {'lab_config': config}),
+        (tree_path, LabHandler, {'lab_config': config})
     ]
 
     # Cache all or none of the files depending on the `cache_files` setting.
@@ -197,16 +200,18 @@ def add_handlers(web_app, config):
 
     # Handle local static assets.
     if config.static_dir:
-        config.public_url = ujoin(base_url, default_public_url)
-        handlers.append((config.public_url + '(.*)', FileFindHandler, {
+        public_path = ujoin(base_url, config.public_url + '(.*)')
+        handlers.append((public_path, FileFindHandler, {
             'path': config.static_dir,
             'no_cache_paths': no_cache_paths
         }))
 
     # Handle local settings.
     if config.schemas_dir:
-        config.settings_url = ujoin(base_url, default_settings_url)
-        settings_path = config.settings_url + '(?P<section_name>.+)'
+        settings_path = ujoin(
+            base_url,
+            config.settings_url + '(?P<section_name>.+)'
+        )
         handlers.append((settings_path, SettingsHandler, {
             'app_settings_dir': config.app_settings_dir,
             'schemas_dir': config.schemas_dir,
@@ -216,22 +221,21 @@ def add_handlers(web_app, config):
     # Handle saved workspaces.
     if config.workspaces_dir:
         # Handle JupyterLab client URLs that include workspaces.
-        config.workspaces_url = ujoin(base_url, default_workspaces_url)
-        workspaces_path = ujoin(config.workspaces_url, r'/.+')
+        workspaces_path = ujoin(base_url, config.workspaces_url, r'/.+')
         handlers.append((workspaces_path, LabHandler, {'lab_config': config}))
 
-        # Handle API requests for workspaces.
-        config.workspaces_api_url = ujoin(base_url, default_workspaces_api_url)
-
         # Handle requests for the list of workspaces. Make slash optional.
-        workspaces_api_path = config.workspaces_api_url + '?'
+        workspaces_api_path = ujoin(base_url, config.workspaces_api_url + '?')
         handlers.append((workspaces_api_path, WorkspacesHandler, {
             'workspaces_url': config.workspaces_url,
             'path': config.workspaces_dir
         }))
 
         # Handle requests for an individually named workspace.
-        workspace_api_path = config.workspaces_api_url + '(?P<space_name>.+)'
+        workspace_api_path = ujoin(
+            base_url,
+            config.workspaces_api_url + '(?P<space_name>.+)'
+        )
         handlers.append((workspace_api_path, WorkspacesHandler, {
             'workspaces_url': config.workspaces_url,
             'path': config.workspaces_dir
@@ -239,9 +243,9 @@ def add_handlers(web_app, config):
 
     # Handle local themes.
     if config.themes_dir:
-        config.themes_url = ujoin(base_url, default_themes_url)
+        themes_path = ujoin(base_url, config.themes_url, '(.*)')
         handlers.append((
-            ujoin(config.themes_url, '(.*)'),
+            themes_path,
             ThemesHandler,
             {
                 'themes_url': config.themes_url,
diff --git a/jupyterlab_launcher/tests/test_workspaces_api.py b/jupyterlab_launcher/tests/test_workspaces_api.py
index bf1cf817..d3ffe282 100644
--- a/jupyterlab_launcher/tests/test_workspaces_api.py
+++ b/jupyterlab_launcher/tests/test_workspaces_api.py
@@ -4,6 +4,7 @@
 import shutil
 
 from jupyterlab_launcher.tests.utils import LabTestBase, APITester
+from notebook.tests.launchnotebook import assert_http_error
 
 
 class WorkspacesAPI(APITester):
@@ -37,11 +38,10 @@ def setUp(self):
         self.workspaces_api = WorkspacesAPI(self.request)
 
     def test_delete(self):
-        orig = 'foo'
+        orig = 'f/o/o/'
         copy = 'baz'
         data = self.workspaces_api.get(orig).json()
         data['metadata']['id'] = copy
-
         assert self.workspaces_api.put(copy, data).status_code == 204
         assert self.workspaces_api.delete(copy).status_code == 204
 
@@ -51,7 +51,7 @@ def test_get(self):
         assert self.workspaces_api.get(id).json()['metadata']['id'] == id
 
     def test_listing(self):
-        listing = set(['foo', 'bar'])
+        listing = set(['foo', 'f/o/o/'])
 
         assert set(self.workspaces_api.get().json()['workspaces']) == listing
 
@@ -60,3 +60,11 @@ def test_put(self):
         data = self.workspaces_api.get(id).json()
 
         assert self.workspaces_api.put(id, data).status_code == 204
+
+    def test_bad_put(self):
+        orig = 'foo'
+        copy = 'bar'
+        data = self.workspaces_api.get(orig).json()
+
+        with assert_http_error(400):
+            self.workspaces_api.put(copy, data)
diff --git a/jupyterlab_launcher/tests/workspaces/abfoo-19e2.jupyterlab-workspace b/jupyterlab_launcher/tests/workspaces/abfoo-19e2.jupyterlab-workspace
new file mode 100644
index 00000000..e9d9e1f0
--- /dev/null
+++ b/jupyterlab_launcher/tests/workspaces/abfoo-19e2.jupyterlab-workspace
@@ -0,0 +1 @@
+{"data": {}, "metadata": {"id": "f/o/o/"}}
diff --git a/jupyterlab_launcher/tests/workspaces/foo.jupyterlab-workspace b/jupyterlab_launcher/tests/workspaces/abfoo-2c26.jupyterlab-workspace
similarity index 100%
rename from jupyterlab_launcher/tests/workspaces/foo.jupyterlab-workspace
rename to jupyterlab_launcher/tests/workspaces/abfoo-2c26.jupyterlab-workspace
diff --git a/jupyterlab_launcher/tests/workspaces/bar.jupyterlab-workspace b/jupyterlab_launcher/tests/workspaces/bar.jupyterlab-workspace
deleted file mode 100644
index 1252c5ac..00000000
--- a/jupyterlab_launcher/tests/workspaces/bar.jupyterlab-workspace
+++ /dev/null
@@ -1 +0,0 @@
-{"data": {}, "metadata": {"id": "bar"}}
diff --git a/jupyterlab_launcher/workspaces_handler.py b/jupyterlab_launcher/workspaces_handler.py
index 4ea0acf5..dfe5b03d 100644
--- a/jupyterlab_launcher/workspaces_handler.py
+++ b/jupyterlab_launcher/workspaces_handler.py
@@ -2,22 +2,96 @@
 
 # Copyright (c) Jupyter Development Team.
 # Distributed under the terms of the Modified BSD License.
+import hashlib
 import json
 import os
-from tornado import web
+import re
+import sys
+import unicodedata
+import urllib
 
 from notebook.base.handlers import APIHandler, json_errors
+from notebook.utils import url_path_join as ujoin
+from tornado import web
+
+
+PY2 = sys.version_info[0] < 3
+
 
+# A cache of workspace names and their slug file name counterparts.
+_cache = dict()
 
+# The JupyterLab workspace file extension.
 _file_extension = '.jupyterlab-workspace'
 
 
+def _list_workspaces(directory, prefix):
+    workspaces = []
+    if not os.path.exists(directory):
+        return workspaces
+
+    items = [item
+             for item in os.listdir(directory)
+             if item.startswith(prefix) and
+             item.endswith(_file_extension)]
+    items.sort()
+
+    for slug in items:
+        if slug in _cache:
+            workspaces.append(_cache[slug])
+            continue
+        workspace_path = os.path.join(directory, slug)
+        if os.path.exists(workspace_path):
+            with open(workspace_path) as fid:
+                try:  # to load and parse the workspace file.
+                    _cache[slug] = json.load(fid)['metadata']['id']
+                    workspaces.append(_cache[slug])
+                except Exception as e:
+                    raise web.HTTPError(500, str(e))
+    return workspaces
+
+
+def _slug(raw, base, sign=True, max_length=128 - len(_file_extension)):
+    """
+    Use the common superset of raw and base values to build a slug shorter
+    than max_length.
+    Convert spaces to hyphens. Remove characters that aren't alphanumerics
+    underscores, or hyphens. Convert to lowercase. Strip leading and trailing
+    whitespace.
+    Add an optional short signature suffix to prevent collisions.
+    Modified from Django utils:
+    https://github.com/django/django/blob/master/django/utils/text.py
+    """
+    signature = ''
+    if sign:
+        signature = '-' + hashlib.sha256(raw.encode('utf-8')).hexdigest()[:4]
+    base = (base if base.startswith('/') else '/' + base).lower()
+    raw = (raw if raw.startswith('/') else '/' + raw).lower()
+    common = 0
+    limit = min(len(base), len(raw))
+    while common < limit and base[common] == raw[common]:
+        common += 1
+    value = ujoin(base[common:], raw)
+    value = urllib.unquote(value) if PY2 else urllib.parse.unquote(value)
+    value = (unicodedata
+             .normalize('NFKC', value)
+             .encode('ascii', 'ignore')
+             .decode('ascii'))
+    value = re.sub(r'[^\w\s-]', '', value).strip()
+    value = re.sub(r'[-\s]+', '-', value)
+    if signature:
+        return value[:max_length - len(signature)] + signature
+    else:
+        return value[:max_length]
+
+
 class WorkspacesHandler(APIHandler):
 
-    def initialize(self, path, default_filename=None, workspaces_url=None):
+    def initialize(self, path, workspaces_url=None):
         self.workspaces_dir = path
 
     def ensure_directory(self):
+        """Return the workspaces directory if set or raise error if not set."""
         if not self.workspaces_dir:
             raise web.HTTPError(500, 'Workspaces directory is not set')
 
@@ -26,14 +100,18 @@ def ensure_directory(self):
     @json_errors
     @web.authenticated
     def delete(self, space_name):
+        base_url = self.base_url
         directory = self.ensure_directory()
 
         if not space_name:
             raise web.HTTPError(400, 'Workspace name is required for DELETE')
 
-        workspace_path = os.path.join(directory, space_name + _file_extension)
+        slug = _slug(space_name, base_url)
+        workspace_path = os.path.join(directory, slug + _file_extension)
+
         if not os.path.exists(workspace_path):
-            raise web.HTTPError(404, 'Workspace %r not found' % space_name)
+            raise web.HTTPError(404, 'Workspace %r (%r) not found' %
+                                     (space_name, slug))
 
         try:  # to delete the workspace file.
             os.remove(workspace_path)
@@ -44,23 +122,17 @@ def delete(self, space_name):
     @json_errors
     @web.authenticated
     def get(self, space_name=''):
+        base_url = self.base_url
         directory = self.ensure_directory()
 
         if not space_name:
-            if not os.path.exists(directory):
-                return self.finish(json.dumps(dict(workspaces=[])))
+            prefix = _slug('', base_url, sign=False)
+            workspaces = _list_workspaces(directory, prefix)
+            return self.finish(json.dumps(dict(workspaces=workspaces)))
 
-            try:  # to read the contents of the workspaces directory.
-                items = [item[:-len(_file_extension)]
-                         for item in os.listdir(directory)
-                         if item.endswith(_file_extension)]
-                items.sort()
+        slug = _slug(space_name, base_url)
+        workspace_path = os.path.join(directory, slug + _file_extension)
 
-                return self.finish(json.dumps(dict(workspaces=items)))
-            except Exception as e:
-                raise web.HTTPError(500, str(e))
-
-        workspace_path = os.path.join(directory, space_name + _file_extension)
         if os.path.exists(workspace_path):
             with open(workspace_path) as fid:
                 try:  # to load and parse the workspace file.
@@ -68,11 +140,13 @@ def get(self, space_name=''):
                 except Exception as e:
                     raise web.HTTPError(500, str(e))
         else:
-            raise web.HTTPError(404, 'Workspace %r not found' % space_name)
+            raise web.HTTPError(404, 'Workspace %r (%r) not found' %
+                                     (space_name, slug))
 
     @json_errors
     @web.authenticated
     def put(self, space_name):
+        base_url = self.base_url
         directory = self.ensure_directory()
 
         if not os.path.exists(directory):
@@ -92,14 +166,19 @@ def put(self, space_name):
             raise web.HTTPError(400, str(e))
 
         # Make sure metadata ID matches the workspace name.
+        # Transparently support an optional inital root `/`.
         metadata_id = workspace['metadata']['id']
-        if metadata_id != space_name:
+        metadata_id = (metadata_id if metadata_id.startswith('/')
+                       else '/' + metadata_id)
+        if metadata_id != '/' + space_name:
             message = ('Workspace metadata ID mismatch: expected %r got %r'
                        % (space_name, metadata_id))
             raise web.HTTPError(400, message)
 
+        slug = _slug(space_name, base_url)
+        workspace_path = os.path.join(directory, slug + _file_extension)
+
         # Write the workspace data to a file.
-        workspace_path = os.path.join(directory, space_name + _file_extension)
         with open(workspace_path, 'w') as fid:
             fid.write(raw)
 
diff --git a/setup.py b/setup.py
index 7626b3da..e1494c29 100644
--- a/setup.py
+++ b/setup.py
@@ -48,7 +48,7 @@
     }
     setup_args['install_requires'] = [
         'jsonschema>=2.6.0',
-        'notebook>=4.2.0',
+        'notebook>=4.2.0'
     ]
 
 if __name__ == '__main__':