diff --git a/README.md b/README.md
index c80c4a7..810a67b 100644
--- a/README.md
+++ b/README.md
@@ -94,6 +94,7 @@ export LIDARR_API_KEY="your-lidarr-api-key"
 | `--yt-only` | Skip Lidarr. |
 | `-o`, `--root PATH` | Output root folder (default `/media/music`). |
 | `--search-all` | Search all albums when adding an artist to Lidarr. |
+| `--repair` | Re-tag existing downloads under `--root` from source metadata (see below). |
 | `--debug` | Verbose output. |
 
 ### Examples
@@ -115,8 +116,26 @@ export LIDARR_API_KEY="your-lidarr-api-key"
 # YouTube only, lossless preferred
 ./musicfetch --yt-only -q flac "Bonobo - Kerala"
 
-# Download by URL (YouTube Music URL preferred for correct art)
+# Download by URL (single track or playlist/set/album, any yt-dlp site)
 ./musicfetch "https://music.youtube.com/watch?v=xxxxxxxxxxx"
+./musicfetch "https://soundcloud.com/artist/sets/my-mix"
+```
+
+### 🔧 Repair existing tags
+
+`--repair` walks `<root>/<artist>/<source>/` (the `youtube`/`soundcloud`/… download
+folders — Lidarr album folders are skipped), re-fetches authoritative metadata for each
+file using the `[id]` in its filename, and fixes tags (album, year, artist, title). Useful
+when downloads landed with missing album or wrong year. It re-queries the source over the
+network, so run it occasionally, not constantly. Requires `mutagen` (a yt-dlp dependency,
+usually already present). CLI-only — not exposed via the REST API.
+
+```bash
+# Preview what would change (writes nothing)
+./musicfetch --repair -d
+
+# Apply fixes under a specific root
+./musicfetch --repair -o /media/music
 ```
 
 ### 📁 Output Structure
@@ -124,8 +143,10 @@ export LIDARR_API_KEY="your-lidarr-api-key"
 ```text
 <root>/
 ├── Artist Name/
-│   ├── Album Name/   (managed by Lidarr)
-│   └── youtube/      (yt-dlp downloads / fallbacks)
+│   ├── Album Name/    (managed by Lidarr)
+│   ├── youtube/       (YouTube / YouTube Music downloads)
+│   ├── soundcloud/    (SoundCloud downloads)
+│   └── <source>/      (one folder per yt-dlp source)
 ```
 
 ---
diff --git a/musicfetch b/musicfetch
index 8de5cc8..354f65f 100755
--- a/musicfetch
+++ b/musicfetch
@@ -796,6 +796,142 @@ def handle_url(url: str, root: str, quality: str, dry_run: bool):
     download_single(url, root, quality, dry_run)
 
 
+# ---------------------------------------------------------------------------
+# Repair: re-tag existing downloads from source metadata (CLI only)
+# ---------------------------------------------------------------------------
+_AUDIO_EXTS = ("opus", "m4a", "mp3", "flac")
+_TRACK_FILE_RE = re.compile(
+    r"^(?P<title>.*) \[(?P<id>[^\]]+)\]\.(?P<ext>" + "|".join(_AUDIO_EXTS) + r")$")
+# m4a uses atom keys; vorbis/easy formats use plain names.
+_MP4_KEYS = {"artist": "\xa9ART", "title": "\xa9nam", "album": "\xa9alb", "date": "\xa9day"}
+
+
+def _is_source_dir(name: str) -> bool:
+    """True for a yt-dlp-style source folder (youtube/soundcloud/…), so we skip
+    Lidarr album folders (which have spaces/capitals)."""
+    return bool(name) and name == _sanitize_source(name)
+
+
+def _parse_track_file(filename: str):
+    """Return (title, id) parsed from '<title> [<id>].<ext>', else None."""
+    m = _TRACK_FILE_RE.match(filename)
+    return (m.group("title"), m.group("id")) if m else None
+
+
+def _repair_probe_url(source: str, vid: str):
+    """Reconstruct a fetchable URL from (source, id), or None if unsupported."""
+    if source == "youtube":
+        return f"https://music.youtube.com/watch?v={vid}"
+    if source == "soundcloud":
+        return f"https://api.soundcloud.com/tracks/{vid}"
+    return None
+
+
+def _desired_tags(meta: dict) -> dict:
+    """Authoritative tags from yt-dlp metadata (omit empties)."""
+    year = (str(meta.get("release_year") or "")
+            or (meta.get("release_date") or "")[:4]
+            or (meta.get("upload_date") or "")[:4])
+    fields = {
+        "artist": get_artist_from_metadata(meta),
+        "title": meta.get("title", ""),
+        "album": meta.get("album", ""),
+        "date": year,
+    }
+    return {k: v for k, v in fields.items() if v and v != "Unknown Artist"}
+
+
+def _open_audio(path: str):
+    """Return (mutagen_file, key_map) for the path's format, or (None, None)."""
+    import mutagen.flac
+    import mutagen.mp4
+    import mutagen.oggopus
+    from mutagen.easyid3 import EasyID3
+    ext = path.rsplit(".", 1)[-1].lower()
+    if ext == "opus":
+        return mutagen.oggopus.OggOpus(path), None
+    if ext == "m4a":
+        return mutagen.mp4.MP4(path), _MP4_KEYS
+    if ext == "mp3":
+        return EasyID3(path), None
+    if ext == "flac":
+        return mutagen.flac.FLAC(path), None
+    return None, None
+
+
+def _read_tag(audio, key_map, field: str) -> str:
+    k = key_map[field] if key_map else field
+    val = audio.get(k)
+    if not val:
+        return ""
+    return str(val[0]) if isinstance(val, list) else str(val)
+
+
+def repair_file(path: str, source: str, dry_run: bool) -> list[str]:
+    """Re-tag one file from source metadata. Returns the list of changed fields."""
+    parsed = _parse_track_file(os.path.basename(path))
+    if not parsed:
+        dbg(f"skip (no id): {path}")
+        return []
+    _, vid = parsed
+    url = _repair_probe_url(source, vid)
+    if not url:
+        dbg(f"skip (source '{source}' not re-queryable): {path}")
+        return []
+    meta = run_yt_dlp_get_metadata(url)
+    if not meta:
+        dbg(f"skip (no metadata): {path}")
+        return []
+    desired = _desired_tags(meta)
+    try:
+        audio, key_map = _open_audio(path)
+    except Exception as e:  # noqa: BLE001
+        err(f"cannot open {path}: {e}")
+        return []
+    if audio is None:
+        return []
+    changed = []
+    for field, value in desired.items():
+        if _read_tag(audio, key_map, field) != value:
+            changed.append(f"{field}={value}")
+            if not dry_run:
+                audio[key_map[field] if key_map else field] = [value]
+    if changed and not dry_run:
+        audio.save()
+    if changed:
+        prefix = "[dry-run] would set" if dry_run else "set"
+        print(f"{prefix} [{', '.join(changed)}] on {path}")
+    return changed
+
+
+def repair_library(root: str, dry_run: bool) -> tuple[int, int]:
+    """Walk <root>/<artist>/<source>/ and re-tag audio files. Returns (scanned, changed)."""
+    if not os.path.isdir(root):
+        err(f"Root folder not found: {root}")
+        return 0, 0
+    scanned = changed = 0
+    for artist in sorted(os.listdir(root)):
+        adir = os.path.join(root, artist)
+        if not os.path.isdir(adir):
+            continue
+        for source in sorted(os.listdir(adir)):
+            sdir = os.path.join(adir, source)
+            if not os.path.isdir(sdir) or not _is_source_dir(source):
+                continue
+            for fname in sorted(os.listdir(sdir)):
+                if not fname.lower().endswith(_AUDIO_EXTS):
+                    continue
+                scanned += 1
+                try:
+                    if repair_file(os.path.join(sdir, fname), source, dry_run):
+                        changed += 1
+                except Exception as e:  # noqa: BLE001 — one bad file shouldn't abort
+                    err(f"repair failed ({fname}): {e}")
+    verb = "Would repair" if dry_run else "Repaired"
+    print(f"{verb} {changed}/{scanned} files")
+    return scanned, changed
+
+
 # ---------------------------------------------------------------------------
 # Main
 # ---------------------------------------------------------------------------
@@ -816,7 +952,7 @@ def parse_args():
     p = argparse.ArgumentParser(
         prog="musicfetch",
         description="Fetch music via Lidarr (preferred) or YouTube Music.")
-    p.add_argument("query", nargs="+", help="Free-form query or a URL.")
+    p.add_argument("query", nargs="*", help="Free-form query or a URL.")
     p.add_argument("-n", "--noninteractive", action="store_true",
                    help="Auto-pick the top hit, no prompt.")
     p.add_argument("-s", "--ytsearch", action="store_true",
@@ -831,6 +967,8 @@ def parse_args():
     p.add_argument("-o", "--root", default=DEFAULT_ROOT, help=f"Output root (default {DEFAULT_ROOT}).")
     p.add_argument("--search-all", action="store_true",
                    help="Search all albums when adding an artist to Lidarr.")
+    p.add_argument("--repair", action="store_true",
+                   help="Re-tag existing downloads under --root from source metadata.")
     p.add_argument("--debug", action="store_true", help="Verbose output.")
     return p.parse_args()
 
@@ -841,6 +979,14 @@ def main():
     DEBUG = args.debug
     query = " ".join(args.query).strip()
 
+    if args.repair:
+        repair_library(args.root, args.dry_run)
+        return
+
+    if not query:
+        err("Provide a query/URL, or use --repair. See --help.")
+        sys.exit(1)
+
     if args.lidarr_only and args.yt_only:
         err("--lidarr-only and --yt-only are mutually exclusive.")
         sys.exit(1)
diff --git a/tests/test_repair.py b/tests/test_repair.py
new file mode 100644
index 0000000..0baf8d6
--- /dev/null
+++ b/tests/test_repair.py
@@ -0,0 +1,118 @@
+import server.mf  # noqa: F401 — loads musicfetch, registers musicfetch_core
+import musicfetch_core as mf
+
+
+# ---- _is_source_dir ----
+def test_is_source_dir():
+    assert mf._is_source_dir("youtube") is True
+    assert mf._is_source_dir("soundcloud") is True
+    assert mf._is_source_dir("downloads") is True
+    assert mf._is_source_dir("Discovery") is False           # Lidarr album folder
+    assert mf._is_source_dir("Random Access Memories") is False
+    assert mf._is_source_dir("") is False
+
+
+# ---- _parse_track_file ----
+def test_parse_track_file():
+    assert mf._parse_track_file("Under My Skin [nGSNF2l44Zc].opus") == ("Under My Skin", "nGSNF2l44Zc")
+    assert mf._parse_track_file("Ignomon [2202690443].m4a") == ("Ignomon", "2202690443")
+    assert mf._parse_track_file("no-id-here.opus") is None
+    assert mf._parse_track_file("cover.jpg") is None
+
+
+# ---- _repair_probe_url ----
+def test_repair_probe_url():
+    assert mf._repair_probe_url("youtube", "vid") == "https://music.youtube.com/watch?v=vid"
+    assert mf._repair_probe_url("soundcloud", "123") == "https://api.soundcloud.com/tracks/123"
+    assert mf._repair_probe_url("bandcamp", "x") is None
+
+
+# ---- _desired_tags ----
+def test_desired_tags_full():
+    meta = {"artist": "Daft Punk", "title": "Aerodynamic", "album": "Discovery", "release_year": 2001}
+    assert mf._desired_tags(meta) == {"artist": "Daft Punk", "title": "Aerodynamic",
+                                      "album": "Discovery", "date": "2001"}
+
+
+def test_desired_tags_year_fallbacks_and_omits_empty():
+    meta = {"title": "T", "uploader": "Chan", "upload_date": "20230102"}  # no album, no release_year
+    out = mf._desired_tags(meta)
+    assert out["date"] == "2023"
+    assert out["title"] == "T"
+    assert out["artist"] == "Chan"
+    assert "album" not in out  # omitted when empty
+
+
+def test_desired_tags_drops_unknown_artist():
+    meta = {"title": "T"}  # get_artist_from_metadata -> "Unknown Artist"
+    assert "artist" not in mf._desired_tags(meta)
+
+
+# ---- repair_file (fake audio + mocked metadata) ----
+class _FakeAudio(dict):
+    def __init__(self, initial):
+        super().__init__(initial)
+        self.saved = False
+
+    def save(self):
+        self.saved = True
+
+
+def test_repair_file_writes_changed_fields(monkeypatch):
+    monkeypatch.setattr(mf, "run_yt_dlp_get_metadata",
+                        lambda url: {"artist": "Daft Punk", "title": "Aerodynamic",
+                                     "album": "Discovery", "release_year": 2001})
+    audio = _FakeAudio({"artist": ["Daft Punk"], "title": ["Aerodynamic"]})  # album/date missing
+    monkeypatch.setattr(mf, "_open_audio", lambda path: (audio, None))
+    changed = mf.repair_file("X/youtube/Aerodynamic [vid].opus", "youtube", dry_run=False)
+    assert set(changed) == {"album=Discovery", "date=2001"}
+    assert audio["album"] == ["Discovery"]
+    assert audio["date"] == ["2001"]
+    assert audio.saved is True
+
+
+def test_repair_file_dry_run_writes_nothing(monkeypatch):
+    monkeypatch.setattr(mf, "run_yt_dlp_get_metadata",
+                        lambda url: {"artist": "A", "title": "T", "album": "Alb", "release_year": 2020})
+    audio = _FakeAudio({})
+    monkeypatch.setattr(mf, "_open_audio", lambda path: (audio, None))
+    changed = mf.repair_file("X/youtube/T [vid].opus", "youtube", dry_run=True)
+    assert changed  # reports would-change
+    assert audio == {}  # nothing written
+    assert audio.saved is False
+
+
+def test_repair_file_skips_unparseable(monkeypatch):
+    called = {"meta": False}
+    monkeypatch.setattr(mf, "run_yt_dlp_get_metadata",
+                        lambda url: called.update(meta=True) or {})
+    assert mf.repair_file("X/youtube/no-id.opus", "youtube", dry_run=False) == []
+    assert called["meta"] is False  # never hit the network
+
+
+def test_repair_file_skips_unqueryable_source(monkeypatch):
+    monkeypatch.setattr(mf, "run_yt_dlp_get_metadata", lambda url: {"title": "x"})
+    assert mf.repair_file("X/bandcamp/T [id].m4a", "bandcamp", dry_run=False) == []
+
+
+# ---- repair_library (real temp tree, repair_file mocked) ----
+def test_repair_library_scans_only_source_dirs(tmp_path, monkeypatch):
+    root = tmp_path
+    (root / "Daft Punk" / "youtube").mkdir(parents=True)
+    (root / "Daft Punk" / "youtube" / "Aerodynamic [vid].opus").write_text("x")
+    (root / "Daft Punk" / "Discovery").mkdir(parents=True)            # Lidarr album -> skip
+    (root / "Daft Punk" / "Discovery" / "Aerodynamic.flac").write_text("x")
+    (root / "Ephixa" / "soundcloud").mkdir(parents=True)
+    (root / "Ephixa" / "soundcloud" / "Ignomon [123].m4a").write_text("x")
+
+    visited = []
+    monkeypatch.setattr(mf, "repair_file",
+                        lambda path, source, dry_run: visited.append((source, path)) or ["album=X"])
+    scanned, changed = mf.repair_library(str(root), dry_run=False)
+    assert scanned == 2 and changed == 2
+    sources = sorted(s for s, _ in visited)
+    assert sources == ["soundcloud", "youtube"]   # Discovery album folder skipped
+
+
+def test_repair_library_missing_root(monkeypatch):
+    assert mf.repair_library("/no/such/dir", dry_run=False) == (0, 0)