diff --git a/clean_dataset.py b/clean_dataset.py
new file mode 100644
index 0000000..e75fc8c
--- /dev/null
+++ b/clean_dataset.py
@@ -0,0 +1,126 @@
+"""
+clean.py — Strip browser annotation plugin artifacts from WebMainBench JSONL files.
+
+Fix Method (from issue.md)
+--------------------------
+_ANNOTATION_TAG_RE = re.compile(
+    r'</?(?:marked-tail|marked-text|marked-inline)[^>]*>', re.IGNORECASE
+)
+_ANNO_ATTR_RE = re.compile(r'\\s+data-anno-uid="[^"]*"', re.IGNORECASE)
+
+def clean_html(html: str) -> str:
+    html = _ANNOTATION_TAG_RE.sub('', html)
+    html = _ANNO_ATTR_RE.sub('', html)
+    return html
+
+Cleaned fields: html, main_html (both present in the dataset)
+"""
+
+import json
+import re
+import argparse
+from pathlib import Path
+
+# ---------------------------------------------------------------------------
+# Compiled patterns (strictly from issue.md)
+# ---------------------------------------------------------------------------
+
+_ANNOTATION_TAG_RE = re.compile(
+    r'</?(?:marked-tail|marked-text|marked-inline)[^>]*>',
+    re.IGNORECASE,
+)
+
+_ANNO_ATTR_RE = re.compile(
+    r'\s+data-anno-uid="[^"]*"',
+    re.IGNORECASE,
+)
+
+
+def clean_html(html: str) -> str:
+    """Strip browser annotation plugin artifacts from saved HTML."""
+    html = _ANNOTATION_TAG_RE.sub('', html)
+    html = _ANNO_ATTR_RE.sub('', html)
+    return html
+
+
+# ---------------------------------------------------------------------------
+# Stats helpers
+# ---------------------------------------------------------------------------
+
+_MARKED_TAIL_RE = re.compile(r'</?marked-tail', re.IGNORECASE)
+_MARKED_TEXT_RE = re.compile(r'</?marked-text', re.IGNORECASE)
+
+
+def collect_stats(html: str) -> dict:
+    return {
+        'marked_tail': bool(_MARKED_TAIL_RE.search(html)),
+        'marked_text': bool(_MARKED_TEXT_RE.search(html)),
+        'anno_uid':    bool(_ANNO_ATTR_RE.search(html)),
+    }
+
+
+# ---------------------------------------------------------------------------
+# Main processing
+# ---------------------------------------------------------------------------
+
+HTML_FIELDS = ('html', 'main_html')
+
+
+def process_file(src: Path, dst: Path) -> dict:
+    """Clean src, write to dst, return aggregate stats."""
+    totals = {'marked_tail': 0, 'marked_text': 0, 'anno_uid': 0}
+    n_records = 0
+
+    with src.open(encoding='utf-8') as fin, dst.open('w', encoding='utf-8') as fout:
+        for raw in fin:
+            raw = raw.strip()
+            if not raw:
+                continue
+            obj = json.loads(raw)
+            n_records += 1
+
+            for field in HTML_FIELDS:
+                val = obj.get(field)
+                if not isinstance(val, str):
+                    continue
+                stats = collect_stats(val)
+                for k, v in stats.items():
+                    if v:
+                        totals[k] += 1
+                obj[field] = clean_html(val)
+
+            fout.write(json.dumps(obj, ensure_ascii=False) + '\n')
+
+    return {'n_records': n_records, **totals}
+
+
+DEFAULT_INPUTS = [
+    'data/WebMainBench_545.jsonl',
+    'data/webmainbench.jsonl',
+]
+DEFAULT_OUTDIR = 'cleaned_output'
+
+
+def main():
+    parser = argparse.ArgumentParser(description='Clean WebMainBench JSONL files')
+    parser.add_argument('inputs', nargs='*', default=DEFAULT_INPUTS, help='Input JSONL file(s)')
+    parser.add_argument('--outdir', default=DEFAULT_OUTDIR, help='Output directory (default: cleaned_output)')
+    args = parser.parse_args()
+
+    outdir = Path(args.outdir)
+    outdir.mkdir(parents=True, exist_ok=True)
+
+    for src_path in args.inputs:
+        src = Path(src_path)
+        dst = outdir / (src.stem + '_cleaned' + src.suffix)
+        print(f'Processing {src} → {dst}')
+        stats = process_file(src, dst)
+        print(f"  Records     : {stats['n_records']}")
+        print(f"  marked-tail : {stats['marked_tail']}")
+        print(f"  marked-text : {stats['marked_text']}")
+        print(f"  anno-uid    : {stats['anno_uid']}")
+        print()
+
+
+if __name__ == '__main__':
+    main()