diff --git a/.gitignore b/.gitignore
index 91f71ce..844c89b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,6 @@ __pycache__
 !vocab_base.txt
 !requirements.txt
 !util/tl_inspector/TLInspector.js
+util/ace/*.exe
+util/ace/.tools_version.json
+!util/ace/offline/*.exe
diff --git a/README.md b/README.md
index 6dcfd1b..5ace3e1 100644
--- a/README.md
+++ b/README.md
@@ -4,7 +4,7 @@ An AI-powered game translation tool with a GUI. Translate RPG Maker, Ren'Py, Tyr
 
 ## Credits
 
-- **[Sinflower](https://github.com/Sinflower)** — [RV2JSON](https://github.com/Sinflower/RV2JSON) — enables RPGMaker Ace games to be translated the same way as MV/MZ by converting rvdata2 files to JSON and back.
+- **[Sinflower](https://github.com/Sinflower)** — [RV2JSON](https://github.com/Sinflower/RV2JSON) — enables RPGMaker Ace games to be translated the same way as MV/MZ by converting rvdata2 files to JSON and back. A copy is bundled offline in `util/ace/offline/`; newer builds are downloaded when online.
 - **Sakura & Kao_SSS** — TL Inspector (`util/tl_inspector/`) — in-game translation source inspector and live-edit plugin for RPG Maker MV/MZ playtesting.
 
 ## Table of Contents
diff --git a/START.bat b/START.bat
index e2e3f3f..9919beb 100644
--- a/START.bat
+++ b/START.bat
@@ -178,6 +178,14 @@ if errorlevel 1 (
 )
 echo.
 
+:: RPG Maker Ace tools (RV2JSON + decrypter) — downloaded from GitHub, not stored in git
+echo Checking RPG Maker Ace tools...
+python -m util.ace.update_tools
+if errorlevel 1 (
+    echo WARNING: Ace tool download failed. Ace translation features may not work until fixed.
+)
+echo.
+
 :: Launch the GUI
 echo ==========================================
 echo    Launching DazedMTLTool GUI...
diff --git a/gui/main.py b/gui/main.py
index 211752d..62bb8dd 100644
--- a/gui/main.py
+++ b/gui/main.py
@@ -132,6 +132,12 @@ class UpdateThread(QThread):
                     shutil.copy2(src, dst)
 
         Path(self.SHA_FILE).write_text(latest_sha)
+        try:
+            from util.ace.update_tools import ensure_ace_tools
+            self.progress.emit("Updating RPG Maker Ace tools…")
+            ensure_ace_tools(log_fn=lambda m: self.progress.emit(m))
+        except Exception as exc:
+            self.progress.emit(f"Ace tool update skipped: {exc}")
         self.finished.emit(True, f"updated:{latest_sha[:8]}")
 
 
diff --git a/gui/workflow_tab.py b/gui/workflow_tab.py
index 7bc706c..bbdb8ba 100644
--- a/gui/workflow_tab.py
+++ b/gui/workflow_tab.py
@@ -3868,7 +3868,12 @@ class WorkflowTab(QWidget):
 
     @staticmethod
     def _ace_tool_path(name: str) -> Path:
-        return Path(__file__).resolve().parent.parent / "util" / "ace" / name
+        from util.ace.update_tools import ace_tool_path
+        return ace_tool_path(name)
+
+    def _ensure_ace_tools(self) -> bool:
+        from util.ace.update_tools import ensure_ace_tools
+        return ensure_ace_tools(log_fn=self._log)
 
     def _show_ace_decrypt_notice(self, game_root: str, rgss_path: str):
         """Show a dialog explaining how to decrypt the encrypted Ace archive."""
@@ -3895,12 +3900,17 @@ class WorkflowTab(QWidget):
             self._run_ace_decrypter(game_root)
 
     def _run_ace_decrypter(self, game_root: str):
-        decrypter = self._ace_tool_path("RPGMakerDecrypter.exe")
-        if not decrypter.is_file():
-            self._log(f"❌ RPGMakerDecrypter.exe not found at {decrypter}")
+        if not self._ensure_ace_tools():
             return
-        self._log(f"Running RPGMakerDecrypter.exe in {game_root} …")
-        w = _SubprocessWorker([str(decrypter)], cwd=game_root, label="RPGMakerDecrypter")
+        try:
+            from util.ace.update_tools import build_decrypter_command
+            cmd = build_decrypter_command(Path(game_root))
+        except FileNotFoundError as exc:
+            self._log(f"❌ {exc}")
+            return
+        decrypter = Path(cmd[0])
+        self._log(f"Running {decrypter.name} in {game_root} …")
+        w = _SubprocessWorker(cmd, cwd=game_root, label=decrypter.stem)
         w.log.connect(self._log)
         w.done.connect(lambda ok, msg: self._log(("✅ " if ok else "❌ ") + msg))
         self._worker = w
@@ -3908,6 +3918,8 @@ class WorkflowTab(QWidget):
 
     def _run_rv2json_create(self):
         """Run RV2JSON.exe -c to convert rvdata2 → JSON files (run from game root)."""
+        if not self._ensure_ace_tools():
+            return
         rv2json = self._ace_tool_path("RV2JSON.exe")
         if not rv2json.is_file():
             self._log(f"❌ RV2JSON.exe not found at {rv2json}")
@@ -3962,6 +3974,8 @@ class WorkflowTab(QWidget):
 
     def _run_rv2json_update(self):
         """Run RV2JSON.exe -u to write translated JSON back to rvdata2 files."""
+        if not self._ensure_ace_tools():
+            return
         rv2json = self._ace_tool_path("RV2JSON.exe")
         if not rv2json.is_file():
             self._log(f"❌ RV2JSON.exe not found at {rv2json}")
diff --git a/start_gui.py b/start_gui.py
index 19860d9..1a7a3d4 100644
--- a/start_gui.py
+++ b/start_gui.py
@@ -43,6 +43,12 @@ def main():
     # Check dependencies
     if not check_dependencies():
         sys.exit(1)
+
+    try:
+        from util.ace.update_tools import ensure_ace_tools
+        ensure_ace_tools()
+    except Exception as exc:
+        print(f"Warning: Ace tool setup failed ({exc}). Ace features may be unavailable.")
         
     # Import and run GUI
     try:
diff --git a/util/ace/__init__.py b/util/ace/__init__.py
new file mode 100644
index 0000000..eee6e89
--- /dev/null
+++ b/util/ace/__init__.py
@@ -0,0 +1,3 @@
+"""RPG Maker Ace helper binaries (downloaded on demand, not committed to git)."""
+
+__all__ = ["ace_tool_path", "build_decrypter_command", "ensure_ace_tools"]
diff --git a/util/ace/offline/RPGMakerDecrypter-cli.exe b/util/ace/offline/RPGMakerDecrypter-cli.exe
new file mode 100644
index 0000000..ada7c59
Binary files /dev/null and b/util/ace/offline/RPGMakerDecrypter-cli.exe differ
diff --git a/util/ace/RV2JSON.exe b/util/ace/offline/RV2JSON.exe
similarity index 100%
rename from util/ace/RV2JSON.exe
rename to util/ace/offline/RV2JSON.exe
diff --git a/util/ace/update_tools.py b/util/ace/update_tools.py
new file mode 100644
index 0000000..e9b4709
--- /dev/null
+++ b/util/ace/update_tools.py
@@ -0,0 +1,255 @@
+"""Download / update RPG Maker Ace tools from upstream GitHub releases.
+
+RV2JSON.exe     — https://github.com/Sinflower/RV2JSON (bin/RV2JSON.exe)
+Decrypter CLI   — https://github.com/uuksu/RPGMakerDecrypter (release asset)
+"""
+
+from __future__ import annotations
+
+import json
+import shutil
+import sys
+import urllib.error
+import urllib.request
+from pathlib import Path
+
+ACE_DIR = Path(__file__).resolve().parent
+OFFLINE_DIR = ACE_DIR / "offline"
+VERSION_FILE = ACE_DIR / ".tools_version.json"
+
+RV2JSON_REPO = "Sinflower/RV2JSON"
+RV2JSON_REMOTE = "bin/RV2JSON.exe"
+RV2JSON_LOCAL = ACE_DIR / "RV2JSON.exe"
+
+DECRYPTER_REPO = "uuksu/RPGMakerDecrypter"
+DECRYPTER_ASSET = "RPGMakerDecrypter-cli.exe"
+DECRYPTER_LOCAL = ACE_DIR / "RPGMakerDecrypter-cli.exe"
+# Legacy name shipped in older DazedMTLTool commits (local only, not in git).
+DECRYPTER_LEGACY = ACE_DIR / "RPGMakerDecrypter.exe"
+
+USER_AGENT = "DazedMTLTool"
+
+
+def _load_versions() -> dict:
+    if not VERSION_FILE.is_file():
+        return {}
+    try:
+        return json.loads(VERSION_FILE.read_text(encoding="utf-8"))
+    except Exception:
+        return {}
+
+
+def _save_versions(data: dict) -> None:
+    ACE_DIR.mkdir(parents=True, exist_ok=True)
+    VERSION_FILE.write_text(json.dumps(data, indent=2), encoding="utf-8")
+
+
+def _github_json(url: str) -> dict | list:
+    req = urllib.request.Request(url, headers={"User-Agent": USER_AGENT, "Accept": "application/vnd.github+json"})
+    with urllib.request.urlopen(req, timeout=60) as resp:
+        return json.loads(resp.read().decode("utf-8"))
+
+
+def _download(url: str, dest: Path) -> None:
+    dest.parent.mkdir(parents=True, exist_ok=True)
+    tmp = dest.with_suffix(dest.suffix + ".part")
+    req = urllib.request.Request(url, headers={"User-Agent": USER_AGENT})
+    with urllib.request.urlopen(req, timeout=600) as resp, open(tmp, "wb") as fh:
+        shutil.copyfileobj(resp, fh)
+    tmp.replace(dest)
+
+
+def _log(msg: str, log_fn) -> None:
+    if log_fn:
+        log_fn(msg)
+    else:
+        print(msg, flush=True)
+
+
+def _seed_from_offline(local: Path, offline_name: str, log_fn) -> bool:
+    """Copy a bundled offline exe into the active path if missing."""
+    if local.is_file():
+        return True
+    src = OFFLINE_DIR / offline_name
+    if not src.is_file():
+        return False
+    local.parent.mkdir(parents=True, exist_ok=True)
+    shutil.copy2(src, local)
+    _log(f"Using offline bundled {offline_name}", log_fn)
+    return True
+
+
+def _rv2json_upstream() -> tuple[str, str]:
+    """Return (blob_sha, download_url) for RV2JSON.exe on main."""
+    url = f"https://api.github.com/repos/{RV2JSON_REPO}/contents/{RV2JSON_REMOTE}?ref=main"
+    info = _github_json(url)
+    sha = info.get("sha", "")
+    dl = info.get("download_url") or ""
+    if not sha or not dl:
+        raise RuntimeError(f"Could not resolve {RV2JSON_REPO}/{RV2JSON_REMOTE}")
+    return sha, dl
+
+
+def _decrypter_upstream() -> tuple[str, str]:
+    """Return (release_tag, browser_download_url) for the Windows CLI decrypter."""
+    url = f"https://api.github.com/repos/{DECRYPTER_REPO}/releases/latest"
+    release = _github_json(url)
+    tag = release.get("tag_name") or release.get("name") or "latest"
+    for asset in release.get("assets") or []:
+        if asset.get("name") == DECRYPTER_ASSET:
+            dl = asset.get("browser_download_url") or ""
+            if dl:
+                return tag, dl
+    raise RuntimeError(f"No {DECRYPTER_ASSET} asset in latest {DECRYPTER_REPO} release")
+
+
+def ensure_rv2json(force: bool = False, log_fn=print) -> bool:
+    """Download RV2JSON.exe if missing or upstream changed. Returns True if ready."""
+    _seed_from_offline(RV2JSON_LOCAL, "RV2JSON.exe", log_fn)
+    versions = _load_versions()
+    try:
+        remote_sha, download_url = _rv2json_upstream()
+    except Exception as exc:
+        if RV2JSON_LOCAL.is_file():
+            _log(f"Warning: Could not check RV2JSON update ({exc}); using local copy.", log_fn)
+            return True
+        if _seed_from_offline(RV2JSON_LOCAL, "RV2JSON.exe", log_fn):
+            return True
+        _log(f"ERROR: RV2JSON unavailable ({exc}).", log_fn)
+        return False
+
+    local_sha = versions.get("rv2json_sha", "")
+    if RV2JSON_LOCAL.is_file() and not force and local_sha == remote_sha:
+        return True
+
+    _log(f"Downloading RV2JSON.exe ({RV2JSON_REPO})...", log_fn)
+    try:
+        _download(download_url, RV2JSON_LOCAL)
+    except Exception as exc:
+        if RV2JSON_LOCAL.is_file():
+            _log(f"Warning: RV2JSON update failed ({exc}); keeping existing copy.", log_fn)
+            return True
+        if _seed_from_offline(RV2JSON_LOCAL, "RV2JSON.exe", log_fn):
+            return True
+        _log(f"ERROR: RV2JSON download failed: {exc}", log_fn)
+        return False
+
+    versions["rv2json_sha"] = remote_sha
+    _save_versions(versions)
+    _log("RV2JSON.exe ready", log_fn)
+    return True
+
+
+def ensure_decrypter(force: bool = False, log_fn=print) -> bool:
+    """Download RPGMakerDecrypter CLI if missing or upstream release changed."""
+    _seed_from_offline(DECRYPTER_LOCAL, DECRYPTER_ASSET, log_fn)
+    if DECRYPTER_LOCAL.is_file():
+        pass  # prefer CLI (offline bundle or download)
+    elif DECRYPTER_LEGACY.is_file():
+        _log("Using legacy RPGMakerDecrypter.exe (local).", log_fn)
+        return True
+
+    versions = _load_versions()
+    try:
+        tag, download_url = _decrypter_upstream()
+    except Exception as exc:
+        if DECRYPTER_LOCAL.is_file() or DECRYPTER_LEGACY.is_file():
+            _log(f"Warning: Could not check decrypter update ({exc}); using local copy.", log_fn)
+            return True
+        if _seed_from_offline(DECRYPTER_LOCAL, DECRYPTER_ASSET, log_fn):
+            return True
+        _log(f"ERROR: Decrypter unavailable ({exc}).", log_fn)
+        return False
+
+    local_tag = versions.get("decrypter_tag", "")
+    if DECRYPTER_LOCAL.is_file() and not force and local_tag == tag:
+        return True
+
+    _log(f"Downloading {DECRYPTER_ASSET} ({DECRYPTER_REPO} {tag})...", log_fn)
+    try:
+        _download(download_url, DECRYPTER_LOCAL)
+    except Exception as exc:
+        if DECRYPTER_LOCAL.is_file() or DECRYPTER_LEGACY.is_file():
+            _log(f"Warning: Decrypter update failed ({exc}); keeping existing copy.", log_fn)
+            return True
+        if _seed_from_offline(DECRYPTER_LOCAL, DECRYPTER_ASSET, log_fn):
+            return True
+        _log(f"ERROR: Decrypter download failed: {exc}", log_fn)
+        return False
+
+    versions["decrypter_tag"] = tag
+    _save_versions(versions)
+    _log("RPG Maker decrypter CLI ready", log_fn)
+    return True
+
+
+def ensure_ace_tools(force: bool = False, log_fn=print) -> bool:
+    """Ensure both Ace tools are present (download / update if needed)."""
+    ok_rv = ensure_rv2json(force=force, log_fn=log_fn)
+    ok_dec = ensure_decrypter(force=force, log_fn=log_fn)
+    return ok_rv and ok_dec
+
+
+def ace_tool_path(name: str) -> Path:
+    """Resolve a tool path under util/ace/."""
+    if name == "RV2JSON.exe":
+        return RV2JSON_LOCAL
+    if name in ("RPGMakerDecrypter.exe", "RPGMakerDecrypter-cli.exe"):
+        if DECRYPTER_LOCAL.is_file():
+            return DECRYPTER_LOCAL
+        if DECRYPTER_LEGACY.is_file():
+            return DECRYPTER_LEGACY
+        return DECRYPTER_LOCAL
+    return ACE_DIR / name
+
+
+def build_decrypter_command(game_root: Path) -> list[str]:
+    """Build argv to decrypt Game.rgss* in game_root."""
+    exe = ace_tool_path("RPGMakerDecrypter-cli.exe")
+    if not exe.is_file():
+        raise FileNotFoundError(
+            f"No RPG Maker decrypter found in {ACE_DIR}. "
+            "Run: python -m util.ace.update_tools"
+        )
+    rgss = sorted(game_root.glob("Game.rgss*"))
+    if not rgss:
+        raise FileNotFoundError(f"No Game.rgss* archive in {game_root}")
+    # Legacy GUI exe ran with no args; CLI needs the archive path.
+    if exe.name == DECRYPTER_LEGACY.name:
+        return [str(exe)]
+    return [str(exe), str(rgss[0])]
+
+
+def refresh_offline_bundle(log_fn=print) -> bool:
+    """Download upstream tools into util/ace/offline/ (for maintainers to commit)."""
+    OFFLINE_DIR.mkdir(parents=True, exist_ok=True)
+    ok = True
+    try:
+        _, rv_url = _rv2json_upstream()
+        _log("Refreshing offline RV2JSON.exe...", log_fn)
+        _download(rv_url, OFFLINE_DIR / "RV2JSON.exe")
+    except Exception as exc:
+        _log(f"ERROR: offline RV2JSON refresh failed: {exc}", log_fn)
+        ok = False
+    try:
+        _, dec_url = _decrypter_upstream()
+        _log(f"Refreshing offline {DECRYPTER_ASSET}...", log_fn)
+        _download(dec_url, OFFLINE_DIR / DECRYPTER_ASSET)
+    except Exception as exc:
+        _log(f"ERROR: offline decrypter refresh failed: {exc}", log_fn)
+        ok = False
+    if ok:
+        _log("Offline bundle refreshed in util/ace/offline/", log_fn)
+    return ok
+
+
+def main() -> int:
+    if "--refresh-offline" in sys.argv:
+        return 0 if refresh_offline_bundle() else 1
+    force = "--force" in sys.argv or "-f" in sys.argv
+    ok = ensure_ace_tools(force=force)
+    return 0 if ok else 1
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())