diff --git a/.jules/bolt.md b/.jules/bolt.md
index 8ce7ce8f7..45c89ada9 100644
--- a/.jules/bolt.md
+++ b/.jules/bolt.md
@@ -77,3 +77,7 @@
 ## 2024-11-20 - Optimize multiple tuple generation from a single collection
 **Learning:** `build_rule_metadata` derives exactly two collections, `owasp` and `cwe`, from the same references. Replacing its two generator traversals with one explicit loop reduces element visits from about 2N to N. Both versions remain O(N), so this is a constant-factor optimization rather than an asymptotic complexity improvement.
 **Action:** Combine repeated traversal when fixed derived collections share one source, while preserving ordering and classification semantics. Benchmark the production hot path before claiming a material wall-clock improvement.
+
+## 2025-03-01 - O(N*M) List Indexing in SARIF Generation
+**Learning:** Calling `list(dict).index(key)` inside a loop over findings to determine the rule index creates an O(N*M) performance bottleneck, allocating a new list and scanning it linearly for every item.
+**Action:** Use a companion dictionary `rule_indices: dict[str, int] = {}` to map rule IDs to their integer index (e.g., `len(rules)`) when first encountered. This reduces the lookup time complexity to O(1).
diff --git a/appguardrail_core/sarif.py b/appguardrail_core/sarif.py
index ca4a9fb6b..654592fab 100644
--- a/appguardrail_core/sarif.py
+++ b/appguardrail_core/sarif.py
@@ -39,6 +39,7 @@ def findings_to_sarif(
     normalized = normalize_findings(findings)
 
     rules: dict[str, dict[str, Any]] = {}
+    rule_indices: dict[str, int] = {}
     results: list[dict[str, Any]] = []
     for f in normalized:
         rule_id = f["rule_id"]
@@ -63,12 +64,13 @@ def findings_to_sarif(
                     "security-severity": _SECURITY_SEVERITY.get(severity, "2.0"),
                 },
             }
+            rule_indices[rule_id] = len(rules)
             rules[rule_id] = rule
 
         results.append(
             {
                 "ruleId": rule_id,
-                "ruleIndex": list(rules).index(rule_id),
+                "ruleIndex": rule_indices[rule_id],
                 "level": _LEVEL.get(severity, "note"),
                 "message": {"text": f["message"].strip()},
                 "locations": [