From f713b2459b5d91c8adde77ffa59324b82e278638 Mon Sep 17 00:00:00 2001
From: Claire Peng <clairep@spotify.com>
Date: Thu, 9 Apr 2026 10:53:47 +0100
Subject: [PATCH] add note about API Base URL in api-docs plugin Readme

Signed-off-by: Claire Peng <clairep@spotify.com>
---
 plugins/api-docs/README.md | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/plugins/api-docs/README.md b/plugins/api-docs/README.md
index f71b796ec4..d662526f24 100644
--- a/plugins/api-docs/README.md
+++ b/plugins/api-docs/README.md
@@ -340,6 +340,34 @@ import { ApiExplorerPage } from '@backstage/plugin-api-docs';
 />;
 ```
 
+## Troubleshooting
+
+### "Try it out" sends requests to the wrong host
+
+If the **Try it out** feature in the OpenAPI widget sends requests to your Backstage app's URL instead of the actual API host, the OpenAPI spec is missing a `servers` entry.
+When no `servers` field is present, Swagger UI falls back to `window.location.origin` — the current page's host — as the base URL for all requests.
+
+**Fix**: add a `servers` field to your API entity's `spec.definition`:
+
+```yaml
+# catalog-info.yaml
+apiVersion: backstage.io/v1alpha1
+kind: API
+metadata:
+  name: my-api
+spec:
+  type: openapi
+  definition: |
+    openapi: "3.0.0"                                         
+    info:       
+      title: My API
+      version: v1
+    servers:                                                 
+      - url: https://api.example.com/v1   # ← specify your api base URL
+```
+
+If you cannot modify the spec (e.g. it is generated or fetched from an external source), you can work around this by adding a `requestInterceptor` that rewrites the URL — see [Adding `requestInterceptor` to Swagger UI](#adding-requestinterceptor-to-swagger-ui) above.
+
 ## Old Frontend System
 
 If your Backstage app uses the old frontend system, you need to manually wire the plugin into your app as outlined in this section. If you are on the new frontend system, you can skip this.