friendlier error for DOIs without citation metadata

apps/vscode/CHANGELOG.md

@@ -3,6 +3,7 @@
 ## 1.136.0 (Unreleased)
 
 - Reduce memory usage by only starting the language server (LSP) in projects containing Quarto documents (https://github.com/quarto-dev/quarto/pull/1059)
+- Improved the error message shown when inserting a citation from a DOI whose registration agency does not provide citation metadata (<https://github.com/quarto-dev/quarto/pull/1061>).
 
 ## 1.135.0 (Release on 2026-07-08)
 

packages/editor-server/src/server/doi.ts

@@ -28,9 +28,23 @@ export function doiServer() : DOIServer {
   return {
     async fetchCSL(doi: string) : Promise<DOIResult> {
       const url = `${kDOIHost}/${doi}`;
-      return handleResponseWithStatus(
-        () => fetch(url, { headers: { Accept: kCSLJsonFormat } })
-      );
+      return handleResponseWithStatus(async () => {
+        const response = await fetch(url, { headers: { Accept: kCSLJsonFormat } });
+
+        // some registration agencies don't support CSL content negotiation;
+        // for those DOIs the request just redirects to the (HTML) landing
+        // page, so report that rather than failing to parse the page as JSON
+        const contentType = response.headers.get("Content-Type") || "";
+        if (response.ok && !contentType.includes("json")) {
+          throw new Error(
+            "This DOI was found, but no citation data is available for it. " +
+            "This usually means the organization that registered the DOI does not support automatic citation lookup. " +
+            "To cite this work, you can add an entry to your bibliography manually."
+          );
+        }
+
+        return response;
+      });
     }
   }
 }