diff --git a/tornadowebapi/exceptions.py b/tornadowebapi/exceptions.py
index 60bd639..64a3a2e 100644
--- a/tornadowebapi/exceptions.py
+++ b/tornadowebapi/exceptions.py
@@ -44,6 +44,19 @@ class NotFound(WebAPIException):
         return None
 
 
+class Exists(WebAPIException):
+    """Represents a case where the resource could not be created
+    because it already exists. This is generally raised in the
+    create() method if the resource has uniqueness constraints on
+    things other than the exposed id."""
+
+    http_code = httpstatus.CONFLICT
+
+    def representation(self):
+        """Exists does not have a representation, just an error status"""
+        return None
+
+
 class BadRepresentation(WebAPIException):
     """Exception raised when the resource representation is
     invalid or does not contain the appropriate keys.

Add Exists exception
In case we generate a resource that already exists for whatever reason
diff --git a/tornadowebapi/tests/test_webapi.py b/tornadowebapi/tests/test_webapi.py
index e3f3b8b..0b5f7de 100644
--- a/tornadowebapi/tests/test_webapi.py
+++ b/tornadowebapi/tests/test_webapi.py
@@ -107,6 +107,12 @@ class Broken(Resource):
     items = boom
 
 
+class AlreadyPresent(Resource):
+    @gen.coroutine
+    def create(self, *args):
+        raise exceptions.Exists()
+
+
 class TestREST(AsyncHTTPTestCase):
     def setUp(self):
         super().setUp()
@@ -120,6 +126,7 @@ class TestREST(AsyncHTTPTestCase):
         registry.registry.register(Unprocessable)
         registry.registry.register(UnsupportsCollection)
         registry.registry.register(Broken)
+        registry.registry.register(AlreadyPresent)
         app = web.Application(handlers=handlers)
         app.hub = mock.Mock()
         return app
@@ -402,6 +409,12 @@ class TestREST(AsyncHTTPTestCase):
             method="GET")
         self.assertEqual(res.code, httpstatus.METHOD_NOT_ALLOWED)
 
+    def test_exists(self):
+        collection_url = "/api/v1/alreadypresents/"
+
+        res = self.fetch(collection_url, method="POST", body="{}")
+        self.assertEqual(res.code, httpstatus.CONFLICT)
+
 
 class TestRESTFunctions(unittest.TestCase):
     def test_api_handlers(self):

pip install -e .[dev]
parse_log_pytest
requirements.txt
pytest flake8
apt-get update apt-get install -y gcc
3.9
requirements.txt dev-requirements.txt
pytest --no-header -rA --tb=line --color=no -p no:cacheprovider -W ignore::DeprecationWarning
coverage==7.8.0
exceptiongroup==1.2.2
flake8==7.2.0
iniconfig==2.1.0
mccabe==0.7.0
packaging==24.2
pluggy==1.5.0
pycodestyle==2.13.0
pyflakes==3.3.1
pytest==8.3.5
tomli==2.2.1
tornado==6.4.2
-e git+https://github.com/simphony/tornado-webapi.git@a09944d66e3090ad4ab8ce20f8dd1f92a14855b3#egg=tornadowebapi

name: tornado-webapi
channels:
  - defaults
  - https://repo.anaconda.com/pkgs/main
  - https://repo.anaconda.com/pkgs/r
  - conda-forge
dependencies:
  - _libgcc_mutex=0.1=main
  - _openmp_mutex=5.1=1_gnu
  - ca-certificates=2025.2.25=h06a4308_0
  - ld_impl_linux-64=2.40=h12ee557_0
  - libffi=3.4.4=h6a678d5_1
  - libgcc-ng=11.2.0=h1234567_1
  - libgomp=11.2.0=h1234567_1
  - libstdcxx-ng=11.2.0=h1234567_1
  - ncurses=6.4=h6a678d5_0
  - openssl=3.0.16=h5eee18b_0
  - pip=25.0=py39h06a4308_0
  - python=3.9.21=he870216_1
  - readline=8.2=h5eee18b_0
  - setuptools=75.8.0=py39h06a4308_0
  - sqlite=3.45.3=h5eee18b_0
  - tk=8.6.14=h39e8969_0
  - tzdata=2025a=h04d1e81_0
  - wheel=0.45.1=py39h06a4308_0
  - xz=5.6.4=h5eee18b_1
  - zlib=1.2.13=h5eee18b_1
  - pip:
      - coverage==7.8.0
      - exceptiongroup==1.2.2
      - flake8==7.2.0
      - iniconfig==2.1.0
      - mccabe==0.7.0
      - packaging==24.2
      - pluggy==1.5.0
      - pycodestyle==2.13.0
      - pyflakes==3.3.1
      - pytest==8.3.5
      - tomli==2.2.1
      - tornado==6.4.2
prefix: /opt/conda/envs/tornado-webapi

tornadowebapi/tests/test_webapi.py::TestREST::test_exists
tornadowebapi/tests/test_webapi.py::TestREST::test_broken tornadowebapi/tests/test_webapi.py::TestREST::test_create tornadowebapi/tests/test_webapi.py::TestREST::test_delete tornadowebapi/tests/test_webapi.py::TestREST::test_items tornadowebapi/tests/test_webapi.py::TestREST::test_post_non_json tornadowebapi/tests/test_webapi.py::TestREST::test_post_on_resource tornadowebapi/tests/test_webapi.py::TestREST::test_retrieve tornadowebapi/tests/test_webapi.py::TestREST::test_unexistent_resource_type tornadowebapi/tests/test_webapi.py::TestREST::test_unprocessable tornadowebapi/tests/test_webapi.py::TestREST::test_unsupported_methods tornadowebapi/tests/test_webapi.py::TestREST::test_unsupports_collections tornadowebapi/tests/test_webapi.py::TestREST::test_update tornadowebapi/tests/test_webapi.py::TestRESTFunctions::test_api_handlers tornadowebapi/tests/test_webapi.py::TestNonGlobalRegistry::test_non_global_registry
tornadowebapi/exceptions.py
tornadowebapi/exceptions.py