diff --git a/src/specify_cli/__init__.py b/src/specify_cli/__init__.py
index 99d313e12..843c60db3 100644
--- a/src/specify_cli/__init__.py
+++ b/src/specify_cli/__init__.py
@@ -2643,6 +2643,11 @@ def preset_add(
                     console.print(f"[red]Error:[/red] Failed to download: {e}")
                     raise typer.Exit(1)
 
+                if not archive_fmt:
+                    console.print("[red]Error:[/red] Could not determine archive format from URL or Content-Type.")
+                    console.print("Ensure the URL points to a .zip or .tar.gz file.")
+                    raise typer.Exit(1)
+
                 suffix = ".tar.gz" if archive_fmt == "tar.gz" else ".zip"
                 archive_path = Path(tmpdir) / f"preset{suffix}"
                 archive_path.write_bytes(archive_data)
@@ -3652,6 +3657,11 @@ def extension_add(
                             archive_fmt = _detect_archive_format(from_url, content_type)
                         archive_data = response.read()
 
+                    if not archive_fmt:
+                        console.print("[red]Error:[/red] Could not determine archive format from URL or Content-Type.")
+                        console.print("Ensure the URL points to a .zip or .tar.gz file.")
+                        raise typer.Exit(1)
+
                     suffix = ".tar.gz" if archive_fmt == "tar.gz" else ".zip"
                     archive_path = download_dir / f"{extension}-url-download{suffix}"
                     archive_path.write_bytes(archive_data)
@@ -4936,7 +4946,7 @@ def _extract_workflow_yml(archive_path: Path, archive_fmt: str) -> bytes:
                 if f is not None:
                     return f.read()
             except KeyError:
-                pass
+                pass  # Root-level workflow.yml not found; fall through to subdirectory search below.
             # Look in a single top-level subdirectory.
             candidates = [
                 m for m in tf.getmembers()
@@ -5099,7 +5109,7 @@ def workflow_add(
             _validate_and_install_local(source_path, str(source_path))
             return
         elif source_path.is_file() and (
-            source.endswith(".tar.gz") or source.endswith(".tgz") or source.endswith(".zip")
+            source.lower().endswith(".tar.gz") or source.lower().endswith(".tgz") or source.lower().endswith(".zip")
         ):
             # Local archive file containing workflow.yml
             from .extensions import _detect_archive_format
diff --git a/src/specify_cli/extensions.py b/src/specify_cli/extensions.py
index f28c02e9b..27e78925d 100644
--- a/src/specify_cli/extensions.py
+++ b/src/specify_cli/extensions.py
@@ -2151,6 +2151,11 @@ class ExtensionCatalog:
             raise ExtensionError(f"Failed to save extension archive: {e}")
 
         # Choose file extension based on detected format.
+        if not archive_fmt:
+            raise ExtensionError(
+                f"Could not determine archive format for {download_url}. "
+                "Ensure the URL points to a .zip or .tar.gz file."
+            )
         if archive_fmt == "tar.gz":
             archive_filename = f"{extension_id}-{version}.tar.gz"
         else:
diff --git a/src/specify_cli/presets.py b/src/specify_cli/presets.py
index 0d597423e..f8cd3bbba 100644
--- a/src/specify_cli/presets.py
+++ b/src/specify_cli/presets.py
@@ -2331,6 +2331,11 @@ class PresetCatalog:
             raise PresetError(f"Failed to save preset archive: {e}")
 
         # Choose file extension based on detected format.
+        if not archive_fmt:
+            raise PresetError(
+                f"Could not determine archive format for {download_url}. "
+                "Ensure the URL points to a .zip or .tar.gz file."
+            )
         if archive_fmt == "tar.gz":
             archive_filename = f"{pack_id}-{version}.tar.gz"
         else: