diff --git a/README.md b/README.md
index ed0e32c..ec199ee 100644
--- a/README.md
+++ b/README.md
@@ -162,6 +162,26 @@ badsecrets --url http://example.com/contains_bad_secret.html
 
 You can also set a custom user-agent with `--user-agent "user-agent string"` or a proxy with `--proxy http://127.0.0.1` in this mode.
 
+* ASP.NET Viewstate: supply the URL
+
+The `ASPNET_Viewstate` module accepts up to four positional arguments — the viewstate, the `__VIEWSTATEGENERATOR` value, the page URL, and a `ViewStateUserKey`. Order does not matter; each is identified by its shape (8 hex characters is the generator, anything starting with `http://`/`https://` is the URL, anything else is the user key).
+
+```bash
+badsecrets <viewstate> <generator> <url> [viewstateuserkey]
+```
+
+**The URL is not optional for every viewstate.** .NET 4.5 (`DOTNET45`) binds the validation key to the page path through the SP800-108 KDF purpose strings, and `DOTNET40` with `IsolateApps` enabled mixes in an app-path hash. Both are computed from the URL. If you supply only the viewstate and generator, badsecrets has no path to derive from and the HMAC can never validate — you will get `No secrets found :(` even when the machine key is in the list.
+
+```bash
+# Reports nothing on this DOTNET45 viewstate - no path to derive the key from
+badsecrets 3RP87RgckNbfc7fNdaHzH9YLqbIhzpA64gFfWB49lhzHpuHFAAO7C7Dl2zh0dWUqobBb4hwiZJ1a2bhP77aQiwqvVqg= 9BD98A7D
+
+# Same viewstate, with the URL - key is found
+badsecrets 3RP87RgckNbfc7fNdaHzH9YLqbIhzpA64gFfWB49lhzHpuHFAAO7C7Dl2zh0dWUqobBb4hwiZJ1a2bhP77aQiwqvVqg= 9BD98A7D http://10.1.1.43/default2.aspx
+```
+
+This is the usual reason `--url` mode succeeds where passing the same viewstate and generator by hand does not: URL mode always knows the page path. URL mode additionally tries several `ViewStateUserKey` candidates automatically (the empty string, `mono`, any `__VIEWSTATE_KEY` field, and each cookie value on the response), which the manual path does not — so pass the user key explicitly if you know it.
+
 Example output:
 
 ```bash
diff --git a/badsecrets/modules/passive/aspnet_viewstate.py b/badsecrets/modules/passive/aspnet_viewstate.py
index d0df676..bb6e522 100644
--- a/badsecrets/modules/passive/aspnet_viewstate.py
+++ b/badsecrets/modules/passive/aspnet_viewstate.py
@@ -22,7 +22,9 @@
 
 
 class ASPNET_Viewstate(BadsecretsBase):
-    check_secret_args = 3
+    # viewstate, generator, url, ViewStateUserKey. A DOTNET45 viewstate needs the URL to derive
+    # the KDF purposes, so capping this below 4 made url+userkey impossible to supply together.
+    check_secret_args = 4
     # Lower minimum than generic_base64_regex (8 groups) to match short MAC_DISABLED viewstates
     identify_regex = re.compile(
         r"^(?:[A-Za-z0-9+\/]{4}){4,}(?:[A-Za-z0-9+\/]{4}|[A-Za-z0-9+\/]{3}=|[A-Za-z0-9+\/]{2}={2})$"
@@ -57,7 +59,9 @@ class ASPNET_Viewstate(BadsecretsBase):
 
     # Pre-compiled regexes for resolve_args
     _url_pattern = re.compile(r"http[s]?://(?:[a-zA-Z]|[0-9]|[$\-_@.&+]|[!*\\(\\),]|(?:%[0-9a-fA-F][0-9a-fA-F]))+")
-    _generator_pattern = re.compile(r"^[A-F0-9]{8}$")
+    # Case-insensitive: a lowercase generator is still a generator. Matching only uppercase let
+    # one fall through to the ViewStateUserKey branch, silently checking the wrong thing.
+    _generator_pattern = re.compile(r"^[A-F0-9]{8}$", re.IGNORECASE)
 
     def carve_regex(self):
         return self._carve_re_normal
@@ -374,7 +378,8 @@ def resolve_args(self, args):
         for arg in args:
             if arg:
                 if self._generator_pattern.match(arg):
-                    generator = arg
+                    # Canonicalize so downstream path brute-forcing and result strings agree
+                    generator = arg.upper()
                 elif self._url_pattern.match(arg):
                     url = arg
                 else:
diff --git a/tests/aspnet_viewstate_test.py b/tests/aspnet_viewstate_test.py
index 2f230ce..9fc2114 100644
--- a/tests/aspnet_viewstate_test.py
+++ b/tests/aspnet_viewstate_test.py
@@ -792,3 +792,35 @@ def test_dotnet45_viewstate_userkey_carve():
     assert r_list
     found_secret = any(r["type"] == "SecretFound" for r in r_list)
     assert found_secret
+
+
+def test_resolve_args_generator_case_insensitive():
+    """A lowercase generator is still a generator, not a ViewStateUserKey."""
+    x = ASPNETViewstate()
+    for supplied in ("9BD98A7D", "9bd98a7d", "9Bd98A7d"):
+        generator, url, userkey = x.resolve_args((supplied,))
+        assert generator == "9BD98A7D", f"{supplied} resolved to generator {generator}"
+        assert url is None
+        assert userkey is None
+
+
+def test_lowercase_generator_still_cracks():
+    """Same viewstate must crack whether the generator is upper or lower case."""
+    x = ASPNETViewstate()
+    viewstate = "/wEPDwUJODc0MjgwMjkwZGTCdzCrBtl0AFYdKsWX1bQ8DcMilw=="
+    url = "http://10.1.1.43/default2.aspx"
+    for supplied in ("9BD98A7D", "9bd98a7d"):
+        found_key = x.check_secret(viewstate, supplied, url)
+        assert found_key, f"failed to crack with generator {supplied}"
+        assert test_vkey in found_key["secret"]
+
+
+def test_check_all_modules_passes_url_and_userkey_together():
+    """check_secret_args must be wide enough to carry viewstate+generator+url+userkey."""
+    from badsecrets.base import check_all_modules
+
+    results = check_all_modules(vsk_viewstate, vsk_generator, vsk_url, vsk_session_id)
+    assert results
+    found = [r for r in results if r["type"] == "SecretFound" and r["detecting_module"] == "ASPNET_Viewstate"]
+    assert len(found) == 1
+    assert f"ViewStateUserKey: {vsk_session_id}" in found[0]["product"]