diff --git a/src/borgstore/backends/rclone.py b/src/borgstore/backends/rclone.py
index 904e3ea..a54a3f9 100644
--- a/src/borgstore/backends/rclone.py
+++ b/src/borgstore/backends/rclone.py
@@ -44,19 +44,24 @@ def get_rclone_backend(url):
     rclone:remote:
     rclone:remote:path
     """
+
+    if not url.startswith("rclone:"):
+        return None
+
+    try:
+        # Check rclone is on the path
+        info = json.loads(subprocess.check_output([RCLONE, "rc", "--loopback", "core/version"]))
+    except Exception:
+        raise BackendDoesNotExist("rclone binary not found on the path or not working properly")
+    if info["decomposed"] < [1, 57, 0]:
+        raise BackendDoesNotExist(f"rclone version must be at least v1.57.0 - found {info['version']}")
+
     rclone_regex = r"""
         rclone:
         (?P<path>(.*))
     """
     m = re.match(rclone_regex, url, re.VERBOSE)
     if m:
-        # Check rclone is on the path
-        try:
-            info = json.loads(subprocess.check_output([RCLONE, "rc", "--loopback", "core/version"]))
-        except Exception:
-            raise BackendDoesNotExist("rclone binary not found on the path or not working properly")
-        if info["decomposed"] < [1, 57, 0]:
-            raise BackendDoesNotExist(f"rclone version must be at least v1.57.0 - found {info['version']}")
         return Rclone(path=m["path"])
 
 
diff --git a/src/borgstore/backends/s3.py b/src/borgstore/backends/s3.py
index c4fa602..f29982d 100644
--- a/src/borgstore/backends/s3.py
+++ b/src/borgstore/backends/s3.py
@@ -24,9 +24,13 @@ def get_s3_backend(url: str):
     Supports URLs of the form:
     (s3|b2):[profile|(access_key_id:access_key_secret)@][schema://hostname[:port]]/bucket/path
     """
-    if boto3 is None:
+
+    if not url.startswith(("s3:", "b2:")):
         return None
 
+    if boto3 is None:
+        raise BackendDoesNotExist("The S3 backend requires dependencies. Install them with: 'pip install borgstore[s3]'")
+
     # (s3|b2):[profile|(access_key_id:access_key_secret)@][schema://hostname[:port]]/bucket/path
     s3_regex = r"""
         (?P<s3type>(s3|b2)):
diff --git a/src/borgstore/backends/sftp.py b/src/borgstore/backends/sftp.py
index 6906358..99c1ab4 100644
--- a/src/borgstore/backends/sftp.py
+++ b/src/borgstore/backends/sftp.py
@@ -21,6 +21,14 @@
 
 def get_sftp_backend(url):
     """Get SFTP backend from URL."""
+
+    if not url.startswith("sftp:"):
+        return None
+
+    if paramiko is None:
+        raise BackendDoesNotExist("The SFTP backend requires dependencies. Install them with: 'pip install borgstore[sftp]'")
+
+
     # sftp://username@hostname:22/path
     # Notes:
     # - username and port are optional
@@ -34,10 +42,9 @@ def get_sftp_backend(url):
         (?P<hostname>([^:/]+))(?::(?P<port>\d+))?/  # slash as separator, not part of the path
         (?P<path>(.+))  # path may or may not start with a slash, must not be empty
     """
-    if paramiko is not None:
-        m = re.match(sftp_regex, url, re.VERBOSE)
-        if m:
-            return Sftp(username=m["username"], hostname=m["hostname"], port=int(m["port"] or "0"), path=m["path"])
+    m = re.match(sftp_regex, url, re.VERBOSE)
+    if m:
+        return Sftp(username=m["username"], hostname=m["hostname"], port=int(m["port"] or "0"), path=m["path"])
 
 
 class Sftp(BackendBase):