diff --git a/docs/release-control/v6/internal/subsystems/notifications.md b/docs/release-control/v6/internal/subsystems/notifications.md
index c971e68c6..1a548abe6 100644
--- a/docs/release-control/v6/internal/subsystems/notifications.md
+++ b/docs/release-control/v6/internal/subsystems/notifications.md
@@ -822,12 +822,19 @@ outside this bounded change.
 
 ### Bounded diagnostic confidentiality: query representations and bypass callers
 
-Recognised query names are exactly token, apikey, api_key, key, secret and
-password after one URL query decode. Every repeated occurrence is masked,
-including mixed literal/escaped names. Unrelated names, ordering and values
+Recognised query names are token, apikey, api_key, key, secret and
+password, matched case-insensitively after one URL query decode. Every repeated
+occurrence is masked, including mixed literal/escaped names and mixed-case
+spellings. Case folding is limited to diagnostic matching: original query-name
+spelling is retained, and configured outbound URLs are not normalised. Unrelated names, ordering and values
 remain intact; invalid name escapes fail closed. This is diagnostic projection,
 not mutation of configured destinations or a claim to recognise arbitrary secrets.
 
+`TestRedactWebhookMixedCaseQuerySecrets` covers all six recognised names plus
+an escaped mixed-case name through URL, embedded-message and transport-error
+projection. It preserves unrelated lookalikes, the original request URL and
+wrapped error identity; these synthetic cases do not establish customer exposure.
+
 Resolved ntfy must apply the same transport-error projection before both its
 error log and returned error. Common HTTP execution preserves payload bytes,
 event identity and error causes; URLs containing userinfo remain rejected by
diff --git a/internal/notifications/webhook_url_redaction.go b/internal/notifications/webhook_url_redaction.go
index 9a8fa77b2..370fbba9e 100644
--- a/internal/notifications/webhook_url_redaction.go
+++ b/internal/notifications/webhook_url_redaction.go
@@ -63,6 +63,8 @@ func RedactWebhookURLSecrets(urlString string) string {
 	// Decode names exactly once, as net/url does, but retain the original
 	// spelling, order and unrelated values in diagnostic URLs. Inspect every
 	// occurrence rather than Query().Get(), which would miss repeated keys.
+	// Mask recognised credential names regardless of case for diagnostics only;
+	// the destination retains the original, potentially case-sensitive query.
 	parts := strings.Split(parsed.RawQuery, "&")
 	changed := false
 	for i, part := range parts {
@@ -71,7 +73,7 @@ func RedactWebhookURLSecrets(urlString string) string {
 		if err != nil {
 			return invalidWebhookURLDiagnostic
 		}
-		switch decoded {
+		switch strings.ToLower(decoded) {
 		case "token", "apikey", "api_key", "key", "secret", "password":
 			if hasValue {
 				parts[i] = name + "=REDACTED"
diff --git a/internal/notifications/webhook_url_redaction_test.go b/internal/notifications/webhook_url_redaction_test.go
index 6f6babd5c..284a26660 100644
--- a/internal/notifications/webhook_url_redaction_test.go
+++ b/internal/notifications/webhook_url_redaction_test.go
@@ -81,6 +81,32 @@ func TestRedactWebhookURLSecrets(t *testing.T) {
 	}
 }
 
+// Diagnostic masking is deliberately conservative even though a destination
+// may treat query names as case-sensitive. It must not change the request URL.
+func TestRedactWebhookMixedCaseQuerySecrets(t *testing.T) {
+	for _, key := range []string{"TOKEN", "ApiKey", "Api_Key", "KEY", "Secret", "PassWord", "%54oKeN"} {
+		t.Run(key, func(t *testing.T) {
+			raw := "https://example.test/hook?" + key + "=synthetic-secret&token=second-secret&extra_TOKEN=visible&channel=ops"
+			want := "https://example.test/hook?" + key + "=REDACTED&token=REDACTED&extra_TOKEN=visible&channel=ops"
+			if got := RedactWebhookURLSecrets(raw); got != want {
+				t.Errorf("URL = %q, want %q", got, want)
+			}
+			if got := RedactWebhookDiagnosticSecrets("post " + raw + " failed"); got != "post "+want+" failed" {
+				t.Errorf("diagnostic = %q", got)
+			}
+			cause := errors.New("connection refused")
+			original := &url.Error{Op: "Post", URL: raw, Err: cause}
+			redacted := redactWebhookTransportError(original)
+			if strings.Contains(redacted.Error(), "synthetic-secret") || strings.Contains(redacted.Error(), "second-secret") {
+				t.Errorf("transport diagnostic exposed synthetic credential: %v", redacted)
+			}
+			if original.URL != raw || !errors.Is(redacted, cause) {
+				t.Fatal("redaction changed request URL or error identity")
+			}
+		})
+	}
+}
+
 func TestRedactWebhookDiagnosticSecrets(t *testing.T) {
 	tests := map[string]struct {
 		input string