diff --git a/lib/effort-audit.py b/lib/effort-audit.py
new file mode 100755
index 0000000..2b74d13
--- /dev/null
+++ b/lib/effort-audit.py
@@ -0,0 +1,88 @@
+#!/usr/bin/env python3
+"""Sum output/thinking/cache tokens per (scope, model, effort) over Claude Code
+transcripts. scope = main (session jsonl) | sub (subagents/*.jsonl or
+isSidechain records). Read-only. Usage: effort-audit.py [projects-root]"""
+import collections
+import glob
+import json
+import os
+import sys
+
+WEIGHTS = {"in": 1.0, "cc": 1.25, "cr": 0.1, "out": 5.0}  # relative to input price
+FIELDS = ("in", "cc", "cr", "out", "think")
+
+
+def usage_row(usage):
+    """Map one API usage block to the five counted fields."""
+    details = usage.get("output_tokens_details") or {}
+    return {
+        "in": usage.get("input_tokens", 0) or 0,
+        "cc": usage.get("cache_creation_input_tokens", 0) or 0,
+        "cr": usage.get("cache_read_input_tokens", 0) or 0,
+        "out": usage.get("output_tokens", 0) or 0,
+        "think": details.get("thinking_tokens", 0) or 0,
+    }
+
+
+def scan(path, scope, agg):
+    """Add every assistant record of one transcript to agg."""
+    with open(path, errors="ignore") as handle:
+        for line in handle:
+            try:
+                rec = json.loads(line)
+            except ValueError:
+                continue
+            msg = rec.get("message") or {}
+            if rec.get("type") != "assistant" or not msg.get("usage"):
+                continue
+            sub = scope == "sub" or bool(rec.get("isSidechain"))
+            key = ("sub" if sub else "main",
+                   str(msg.get("model", "?")).replace("claude-", ""),
+                   str(rec.get("effort") or "?"))
+            row = usage_row(msg["usage"])
+            agg[key]["msgs"] += 1
+            for field in FIELDS:
+                agg[key][field] += row[field]
+
+
+def weighted(counter):
+    return sum(counter[f] * WEIGHTS[f] for f in WEIGHTS)
+
+
+def report(agg):
+    """Print the per-key table, then the main/sub split and the thinking share."""
+    total = collections.Counter()
+    for counter in agg.values():
+        total.update(counter)
+    total_w = weighted(total) or 1
+    print(f"{'scope':5} {'model':22} {'effort':7} {'msgs':>6} {'think/msg':>9} "
+          f"{'think_tok':>10} {'out_tok':>10} {'cache_read':>12} {'%wcost':>7}")
+    for (scope, model, effort), c in sorted(agg.items(), key=lambda kv: -weighted(kv[1])):
+        per_msg = c["think"] / max(c["msgs"], 1)
+        print(f"{scope:5} {model:22} {effort:7} {c['msgs']:6d} {per_msg:9.0f} "
+              f"{c['think']:10d} {c['out']:10d} {c['cr']:12d} {100 * weighted(c) / total_w:6.1f}%")
+    by_scope = collections.defaultdict(collections.Counter)
+    for (scope, _, _), c in agg.items():
+        by_scope[scope].update(c)
+    for scope, c in by_scope.items():
+        print(f"  {scope:5} weighted-cost {100 * weighted(c) / total_w:5.1f}%  "
+              f"thinking {100 * c['think'] / max(total['think'], 1):5.1f}%  requests {c['msgs']}")
+    print(f"  thinking = {100 * total['think'] * WEIGHTS['out'] / total_w:.1f}% of weighted cost; "
+          f"cache reads = {100 * total['cr'] * WEIGHTS['cr'] / total_w:.1f}%")
+
+
+def main():
+    root = os.path.expanduser(sys.argv[1] if len(sys.argv) > 1 else "~/.claude/projects")
+    agg = collections.defaultdict(collections.Counter)
+    for project in sorted(glob.glob(os.path.join(root, "*"))):
+        if not os.path.isdir(project):
+            continue
+        for path in glob.glob(os.path.join(project, "*.jsonl")):
+            scan(path, "main", agg)
+        for path in glob.glob(os.path.join(project, "*", "subagents", "*.jsonl")):
+            scan(path, "sub", agg)
+    report(agg)
+
+
+if __name__ == "__main__":
+    main()
diff --git a/lib/effort-shift.md b/lib/effort-shift.md
index 85d823c..3d07925 100644
--- a/lib/effort-shift.md
+++ b/lib/effort-shift.md
@@ -28,6 +28,9 @@ max (stuck error, judged need).
   the run stays at the session level. `CLAUDE_CODE_EFFORT_LEVEL` beats every
   frontmatter; keep it unset (the session banner warns).
 
+Measure the split any time: `python3 ~/.claude/lib/effort-audit.py`
+(thinking/output/cache tokens per scope, model and effort).
+
 ## Shifters
 
 `Skill(effort-low)` · `Skill(effort-medium)` · `Skill(effort-high)` ·
diff --git a/lib/tests/effort-routing.test.sh b/lib/tests/effort-routing.test.sh
index b3ef678..6128221 100755
--- a/lib/tests/effort-routing.test.sh
+++ b/lib/tests/effort-routing.test.sh
@@ -87,6 +87,10 @@ has "lib/verify-secure-loop.md" '/effort-max'
 # ── 8) turn-reset re-assert after a prose gate followed by reflection
 has "skills/bugfix/SKILL.md" 'effort-shift: turn reset'
 
+# ── 11) audit tooling
+has "lib/effort-shift.md" 'effort-audit.py'
+[ -x "$R/lib/effort-audit.py" ] && ok || ko "lib/effort-audit.py missing or not executable"
+
 # ── summary (later tasks insert their locks ABOVE this line)
 printf 'effort-routing census: %d pass, %d fail\n' "$pass" "$fail"
 [ "$fail" -eq 0 ]