diff --git a/SETUP/API.md b/SETUP/API.md
index ab5b2c445..6f00a3d1a 100644
--- a/SETUP/API.md
+++ b/SETUP/API.md
@@ -66,3 +66,24 @@ Three settings in `configuration.sh` control limiting:
   allowed per given window.
 * `_API_RATE_LIMIT_SECONDS_IN_WINDOW` - the number of seconds within a given
   window.
+
+## Client Storage
+
+To facilitate javascript UI clients persisting data across browsers and devices,
+the API includes an optional endpoint for clients to store and fetch JSON blobs.
+To enable this feature, add a string for the client to the
+`_API_CLIENT_STORAGE_KEYS` configuration setting and have the client use that
+string with the endpoint as the `clientid`.
+
+Some important notes about this feature:
+* Client storage is one blob per user per client. Said another way: API users are
+  only able to store one blob per `clientid` and that blob is only for the user
+  authenticated with the API.
+* Beyond validating these are valid JSON objects, they are treated as opaque
+  blobs server-side. It is up to the client to manage the object, including
+  the schema and the possibility that the object will not match an expected
+  schema.
+* The `clientid` is not a secret to the browser. Nothing prevents users with
+  API keys (or valid PHP session keys) from using this endpoint with a valid
+  client ID to change the contents of this blob for their user. Clients
+  should treat this blob as unvalidated user input and act accordingly.
diff --git a/SETUP/tests/unittests/ApiTest.php b/SETUP/tests/unittests/ApiTest.php
index bcf0d9416..32e3e5101 100644
--- a/SETUP/tests/unittests/ApiTest.php
+++ b/SETUP/tests/unittests/ApiTest.php
@@ -787,6 +787,9 @@ public function test_pickersets(): void
         $this->assertEquals(["¿", "INVERTED QUESTION MARK"], $pickerset["subsets"][3]["rows"][1][1]);
     }
 
+    //---------------------------------------------------------------------------
+    // tests for documents
+
     public function test_available_italian_documents(): void
     {
         $path = "v1/documents";
@@ -823,6 +826,48 @@ public function test_unavailable_document(): void
         $_SERVER["REQUEST_METHOD"] = "GET";
         $router->route($path, ['language_code' => 'de']);
     }
+
+    //---------------------------------------------------------------------------
+    // tests for storage
+
+    public function test_client_storage_valid(): void
+    {
+        global $pguser;
+        global $api_client_storage_keys;
+        global $request_body;
+
+        $pguser = $this->TEST_USERNAME_PM;
+        array_push($api_client_storage_keys, "valid");
+
+        $path = "v1/storage/clients/valid";
+        $query_params = [];
+        $request_body = ["key" => 1];
+        $router = ApiRouter::get_router();
+
+        $_SERVER["REQUEST_METHOD"] = "PUT";
+        $response = $router->route($path, $query_params);
+        $this->assertEquals($request_body, (array)$response);
+
+        $_SERVER["REQUEST_METHOD"] = "GET";
+        $response = $router->route($path, $query_params);
+        $this->assertEquals($request_body, (array)$response);
+
+        $_SERVER["REQUEST_METHOD"] = "DELETE";
+        $response = $router->route($path, $query_params);
+        $this->assertEquals(null, $response);
+    }
+
+    public function test_client_storage_invalid(): void
+    {
+        $this->expectExceptionCode(4);
+
+        $query_params = [];
+
+        $path = "v1/storage/clients/invalid";
+        $_SERVER["REQUEST_METHOD"] = "GET";
+        $router = ApiRouter::get_router();
+        $router->route($path, $query_params);
+    }
 }
 
 // this mocks the function in index.php
diff --git a/api/dp-openapi.yaml b/api/dp-openapi.yaml
index c69ae9873..b70ce147a 100644
--- a/api/dp-openapi.yaml
+++ b/api/dp-openapi.yaml
@@ -1338,6 +1338,58 @@ paths:
         404:
           $ref: '#/components/responses/NotFound'
 
+  /storage/clients/{clientid}:
+    get:
+      tags:
+      - storage
+      description: Get JSON blob stored by the client
+      parameters:
+      - name: clientid
+        in: path
+        description: Client ID
+        required: true
+        schema:
+          type: string
+      responses:
+        200:
+          description: JSON blob
+          content:
+            application/json:
+              schema:
+                type: object
+    put:
+      tags:
+      - storage
+      description: Save JSON blob for the client
+      parameters:
+      - name: clientid
+        in: path
+        description: Client ID
+        required: true
+        schema:
+          type: string
+      responses:
+        200:
+          description: JSON blob that was persisted
+          content:
+            application/json:
+              schema:
+                type: object
+    delete:
+      tags:
+      - storage
+      description: Delete JSON blob for the client
+      parameters:
+      - name: clientid
+        in: path
+        description: Client ID
+        required: true
+        schema:
+          type: string
+      responses:
+        200:
+          description: JSON blob was deleted
+
 components:
   securitySchemes:
     ApiKeyAuth:
diff --git a/api/v1.inc b/api/v1.inc
index 8607632ab..875c81f12 100644
--- a/api/v1.inc
+++ b/api/v1.inc
@@ -7,6 +7,7 @@ include_once("v1_projects.inc");
 include_once("v1_queues.inc");
 include_once("v1_stats.inc");
 include_once("v1_docs.inc");
+include_once("v1_storage.inc");
 
 $router = ApiRouter::get_router();
 
@@ -18,6 +19,7 @@ $router->add_validator(":pagename", "validate_page_name");
 $router->add_validator(":pageroundid", "validate_page_round");
 $router->add_validator(":queueid", "validate_release_queue");
 $router->add_validator(":document", "validate_document");
+$router->add_validator(":clientid", "validate_client_id");
 
 // Add routes
 $router->add_route("GET", "v1/documents", "api_v1_documents");
@@ -62,3 +64,7 @@ $router->add_route("GET", "v1/stats/site/projects/stages", "api_v1_stats_site_pr
 $router->add_route("GET", "v1/stats/site/projects/states", "api_v1_stats_site_projects_states");
 $router->add_route("GET", "v1/stats/site/rounds", "api_v1_stats_site_rounds");
 $router->add_route("GET", "v1/stats/site/rounds/:roundid", "api_v1_stats_site_round");
+
+$router->add_route("GET", "v1/storage/clients/:clientid", "api_v1_storage_clients");
+$router->add_route("PUT", "v1/storage/clients/:clientid", "api_v1_storage_clients");
+$router->add_route("DELETE", "v1/storage/clients/:clientid", "api_v1_storage_clients_delete");
diff --git a/api/v1_storage.inc b/api/v1_storage.inc
new file mode 100644
index 000000000..4c5dd76de
--- /dev/null
+++ b/api/v1_storage.inc
@@ -0,0 +1,32 @@
+<?php
+
+// DP API v1 -- Storage
+
+//===========================================================================
+// storage/clients/:clientid
+
+/** @return mixed */
+function api_v1_storage_clients(string $method, array $data, array $query_params)
+{
+    global $pguser;
+
+    $clientid = $data[":clientid"];
+
+    $storage = new ApiClientStorage($clientid, $pguser);
+    if ($method == "GET") {
+        return json_decode($storage->get());
+    } elseif ($method == "PUT") {
+        $storage->set(json_encode(api_get_request_body()));
+        return json_decode($storage->get());
+    }
+}
+
+function api_v1_storage_clients_delete(string $method, array $data, array $query_params): void
+{
+    global $pguser;
+
+    $clientid = $data[":clientid"];
+
+    $storage = new ApiClientStorage($clientid, $pguser);
+    $storage->delete();
+}
diff --git a/api/v1_validators.inc b/api/v1_validators.inc
index 2615f2531..39763d0c6 100644
--- a/api/v1_validators.inc
+++ b/api/v1_validators.inc
@@ -77,3 +77,13 @@ function validate_document(string $document): string
     }
     return $document;
 }
+
+function validate_client_id(string $clientid, array $data): string
+{
+    global $api_client_storage_keys;
+
+    if (!in_array($clientid, $api_client_storage_keys)) {
+        throw new NotFoundError("$clientid is not a valid client id");
+    }
+    return $clientid;
+}