diff --git a/spec/namespaces/cat.yaml b/spec/namespaces/cat.yaml
index e62e86ea5..176c0d38c 100644
--- a/spec/namespaces/cat.yaml
+++ b/spec/namespaces/cat.yaml
@@ -869,6 +869,11 @@ components:
             type: array
             items:
               $ref: '../schemas/cat.indices.yaml#/components/schemas/IndicesRecord'
+        application/yaml:
+          schema:
+            type: array
+            items:
+              $ref: '../schemas/cat.indices.yaml#/components/schemas/IndicesRecord'
     cat.master@200:
       description: ''
       content:
@@ -879,6 +884,11 @@ components:
             type: array
             items:
               $ref: '../schemas/cat.master.yaml#/components/schemas/MasterRecord'
+        application/yaml:
+          schema:
+            type: array
+            items:
+              $ref: '../schemas/cat.health.yaml#/components/schemas/MasterRecord'
     cat.nodeattrs@200:
       description: ''
       content:
diff --git a/spec/schemas/cat.indices.yaml b/spec/schemas/cat.indices.yaml
index c03496f7b..974f4cbfc 100644
--- a/spec/schemas/cat.indices.yaml
+++ b/spec/schemas/cat.indices.yaml
@@ -29,13 +29,13 @@ components:
           type: string
         docs.count:
           description: available docs
-          oneOf:
+          anyOf:
             - type: string
             - nullable: true
               type: string
         docs.deleted:
           description: deleted docs
-          oneOf:
+          anyOf:
             - type: string
             - nullable: true
               type: string
@@ -47,13 +47,13 @@ components:
           type: string
         store.size:
           description: store size of primaries & replicas
-          oneOf:
+          anyOf:
             - type: string
             - nullable: true
               type: string
         pri.store.size:
           description: store size of primaries
-          oneOf:
+          anyOf:
             - type: string
             - nullable: true
               type: string
diff --git a/tests/cat/indices.yaml b/tests/cat/indices.yaml
new file mode 100644
index 000000000..f1a14b422
--- /dev/null
+++ b/tests/cat/indices.yaml
@@ -0,0 +1,73 @@
+$schema: ../../json_schemas/test_story.schema.yaml
+
+description: Test cat/indices endpoints.
+prologues:
+  - synopsis: Create an index named `books` with mappings and settings.
+    path: /{index}
+    method: PUT
+    parameters:
+      index: books
+    request_body:
+      payload: {}
+epilogues:
+  - path: /books
+    method: DELETE
+    status: [200, 404]
+chapters:
+  - synopsis: Cat with a default text response.
+    method: GET
+    path: /_cat/indices
+    response:
+      status: 200
+      content_type: text/plain
+  - synopsis: Cat with verbose output (v=true).
+    method: GET
+    path: /_cat/indices
+    parameters:
+      v: true
+    response:
+      status: 200
+      content_type: text/plain
+  - synopsis: Cat with headers (h=header1,header2).
+    method: GET
+    path: /_cat/indices
+    parameters:
+      h:
+        - health
+        - status
+    response:
+      status: 200
+      content_type: text/plain
+  - synopsis: Cat displaying all available headers (help=true).
+    method: GET
+    path: /_cat/indices
+    parameters:
+      help: true
+    response:
+      status: 200
+      content_type: text/plain
+  - synopsis: Cat with sorted results.
+    method: GET
+    path: /_cat/indices
+    parameters:
+      s:
+        - status
+    response:
+      status: 200
+      content_type: text/plain
+  - synopsis: Cat in different formats (format=json).
+    method: GET
+    path: /_cat/indices
+    parameters:
+      format: json
+    response:
+      status: 200
+      content_type: application/json
+  - synopsis: Cat in different formats (format=yaml).
+    method: GET
+    path: /_cat/indices
+    parameters:
+      format: yaml
+    response:
+      status: 200
+      content_type: application/yaml