diff --git a/fern/apis/api/generators.yml b/fern/apis/api/generators.yml
index 06857510a..f9bc714a1 100644
--- a/fern/apis/api/generators.yml
+++ b/fern/apis/api/generators.yml
@@ -3,6 +3,7 @@ api:
   specs:
     - openapi: ./openapi.json
       overrides: ./openapi-overrides.yml
+      overlays: ./openapi-parameter-descriptions-overlay.yml
       origin: https://api.vapi.ai/api-json
       settings:
         title-as-schema-name: false
diff --git a/fern/apis/api/openapi-parameter-descriptions-overlay.yml b/fern/apis/api/openapi-parameter-descriptions-overlay.yml
new file mode 100644
index 000000000..db5fb73b6
--- /dev/null
+++ b/fern/apis/api/openapi-parameter-descriptions-overlay.yml
@@ -0,0 +1,77 @@
+overlay: 1.0.0
+info:
+  title: Document API parameters
+  version: 1.0.0
+actions:
+  # Path parameters
+  - target: $.paths['/assistant/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the assistant.
+  - target: $.paths['/squad/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the squad.
+  - target: $.paths['/call/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the call.
+  - target: $.paths['/campaign/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the campaign.
+  - target: $.paths['/phone-number/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the phone number.
+  - target: $.paths['/tool/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the tool.
+  - target: $.paths['/file/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the file.
+  - target: $.paths['/structured-output/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the structured output.
+  - target: $.paths['/reporting/insight/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the reporting insight.
+  - target: $.paths['/reporting/insight/{id}/run'].post.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the reporting insight.
+  - target: $.paths['/eval/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the eval definition.
+  - target: $.paths['/eval/run/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the eval run.
+  - target: $.paths['/observability/scorecard/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the scorecard.
+  - target: $.paths['/provider/{provider}/{resourceName}/{id}'].*.parameters[?(@.name == 'id' && @.in == 'path')]
+    update:
+      description: The unique identifier of the provider resource.
+
+  # Query parameters
+  - target: $.paths['/campaign'].get.parameters[?(@.name == 'id' && @.in == 'query')]
+    update:
+      description: Filters campaigns by ID.
+  - target: $.paths['/campaign'].get.parameters[?(@.name == 'status' && @.in == 'query')]
+    update:
+      description: Filters campaigns by status.
+  - target: $.paths['/structured-output/{id}'].patch.parameters[?(@.name == 'schemaOverride' && @.in == 'query')]
+    update:
+      description: Set to the string `true` to allow changing the schema's top-level type. Other values do not enable schema type changes.
+  - target: $.paths['/reporting/insight'].get.parameters[?(@.name == 'id' && @.in == 'query')]
+    update:
+      description: Filters reporting insights by ID.
+  - target: $.paths['/eval'].get.parameters[?(@.name == 'id' && @.in == 'query')]
+    update:
+      description: Filters eval definitions by ID.
+  - target: $.paths['/eval/run'].get.parameters[?(@.name == 'id' && @.in == 'query')]
+    update:
+      description: Filters eval runs by ID.
+  - target: $.paths['/observability/scorecard'].get.parameters[?(@.name == 'id' && @.in == 'query')]
+    update:
+      description: Filters scorecards by ID.
+  - target: $.paths['/provider/{provider}/{resourceName}'].get.parameters[?(@.name == 'id' && @.in == 'query')]
+    update:
+      description: Filters provider resources by their resource ID.
+  - target: $.paths['/provider/{provider}/{resourceName}'].get.parameters[?(@.name == 'resourceId' && @.in == 'query')]
+    update:
+      description: Filters provider resources by their provider-specific resource ID.