diff --git a/scripts/diagnose_cached_stage_failure.py b/scripts/diagnose_cached_stage_failure.py
index bce66f8..fd3d9fa 100644
--- a/scripts/diagnose_cached_stage_failure.py
+++ b/scripts/diagnose_cached_stage_failure.py
@@ -310,6 +310,17 @@ def _audit_message_terms(texts: list[str], *, available: bool) -> dict[str, bool
     return {term: bool(_AUDIT_MESSAGE_TERM_PATTERNS[term].search(joined)) for term in _AUDIT_MESSAGE_TERMS}
 
 
+def _tag_length_details(texts: list[str]) -> dict[str, Any]:
+    messages = [text for text in texts if _REASON_PATTERNS["traffic_tag_length"].search(text)]
+    text = "\n".join(messages)
+    limits = sorted({int(value) for value in re.findall(r"\b([0-9]{1,2})\s+characters?\b", text, re.I) if 0 < int(value) <= 63})
+    return {
+        "character_limits": limits,
+        "minimum_requirement": bool(re.search(r"at least|minimum|too short|shorter", text, re.I)),
+        "maximum_requirement": bool(re.search(r"at most|maximum|too long|longer|exceed", text, re.I)),
+    }
+
+
 def summarize(
     *,
     service: Any,
@@ -406,6 +417,7 @@ def summarize(
             audit_texts,
             available=audit_status == "ok" and audit_entries_count is not None,
         ),
+        "traffic_tag_length_details": _tag_length_details(audit_texts) if audit_status == "ok" else None,
         **_control_summary(policy, jobs),
         "audit_query_status": audit_status,
         "audit_entry_count": audit_entries_count if audit_status == "ok" else None,
diff --git a/tests/test_cached_stage_failure_diagnostic.py b/tests/test_cached_stage_failure_diagnostic.py
index 3d7dcde..428475c 100644
--- a/tests/test_cached_stage_failure_diagnostic.py
+++ b/tests/test_cached_stage_failure_diagnostic.py
@@ -101,6 +101,7 @@ def test_summary_exposes_only_closed_statuses_counts_and_categories():
         "latest_created_revision_ready": False,
         "latest_revision_error_categories": ["image"],
         "latest_revision_error_status_codes": [],
+        "traffic_tag_length_details": {"character_limits": [], "minimum_requirement": False, "maximum_requirement": False},
         "audit_error_message_terms": {
             "container": False,
             "name": False,
@@ -172,6 +173,17 @@ def test_traffic_tag_rejections_remain_closed(message, reason):
     assert "PRIVATE_TAG" not in json.dumps(summary)
 
 
+def test_tag_limit_details_only_expose_small_explicit_character_limits():
+    summary = diagnostic._tag_length_details([
+        "Traffic tag [PRIVATE_TAG] must be at least 3 characters long",
+        "Traffic tag [PRIVATE_TAG] must be at most 63 characters long",
+        "Traffic tag [PRIVATE_TAG] has 12345678 characters",
+        "Other error requires 8 characters",
+    ])
+    assert summary == {"character_limits": [3, 63], "minimum_requirement": True, "maximum_requirement": True}
+    assert "PRIVATE_TAG" not in json.dumps(summary)
+
+
 def test_missing_logging_permission_is_reported_without_guessing_failure_category():
     service, revisions, policy, jobs, audit = _evidence("permission denied")
     summary = diagnostic.summarize(