diff --git a/libs/openant-core/core/parser_adapter.py b/libs/openant-core/core/parser_adapter.py
index d52c89f..b705db2 100644
--- a/libs/openant-core/core/parser_adapter.py
+++ b/libs/openant-core/core/parser_adapter.py
@@ -11,6 +11,7 @@
 
 import json
 import os
+import shutil
 import subprocess
 import sys
 from pathlib import Path
@@ -21,6 +22,9 @@
 # Root of openant-core (where parsers/ lives)
 _CORE_ROOT = Path(__file__).parent.parent
 
+# JS parser directory (holds its own package.json / node_modules)
+_JS_PARSER_DIR = _CORE_ROOT / "parsers" / "javascript"
+
 # Shared language detection config (single source of truth: config/languages.json)
 _LANGUAGES_CONFIG = Path(__file__).parent.parent.parent.parent / "config" / "languages.json"
 
@@ -324,12 +328,47 @@ def _parse_python(repo_path: str, output_dir: str, processing_level: str, skip_t
 # JavaScript/TypeScript parser
 # ---------------------------------------------------------------------------
 
+def _ensure_js_parser_dependencies() -> None:
+    """Install the JS parser's Node dependencies on first use.
+
+    Mirrors the Go CLI's venv bootstrap (apps/openant-cli/internal/python/runtime.go):
+    the first invocation installs, subsequent invocations are a no-op. Runs only
+    when a JS repo is actually being parsed, so Python/Go-only users never need npm.
+    """
+    if (_JS_PARSER_DIR / "node_modules").is_dir():
+        return
+
+    npm = shutil.which("npm")
+    if npm is None:
+        raise RuntimeError(
+            "JavaScript parser dependencies are not installed and `npm` is not on PATH. "
+            f"Install Node.js/npm, then run: npm install (from {_JS_PARSER_DIR})"
+        )
+
+    print(
+        f"[Parser] Installing JS parser dependencies (first run, this may take a minute)...",
+        file=sys.stderr,
+    )
+    result = subprocess.run(
+        [npm, "install"],
+        cwd=str(_JS_PARSER_DIR),
+        stdout=sys.stderr,
+        stderr=sys.stderr,
+    )
+    if result.returncode != 0:
+        raise RuntimeError(
+            f"`npm install` failed in {_JS_PARSER_DIR} with exit code {result.returncode}"
+        )
+
+
 def _parse_javascript(repo_path: str, output_dir: str, processing_level: str, skip_tests: bool = True, name: str = None) -> ParseResult:
     """Invoke the JavaScript/TypeScript parser.
 
     The JS parser is a PipelineTest class that runs Node.js subprocesses.
     We invoke it via subprocess to avoid the sys.path hacks.
     """
+    _ensure_js_parser_dependencies()
+
     print("[Parser] Running JavaScript parser...", file=sys.stderr)
 
     # Build command — analyzer-path now defaults to co-located file in the parser
diff --git a/libs/openant-core/tests/test_js_parser_bootstrap.py b/libs/openant-core/tests/test_js_parser_bootstrap.py
new file mode 100644
index 0000000..698efc9
--- /dev/null
+++ b/libs/openant-core/tests/test_js_parser_bootstrap.py
@@ -0,0 +1,90 @@
+"""Tests for the JS parser's lazy npm-install bootstrap.
+
+Covers `_ensure_js_parser_dependencies` in core.parser_adapter: behavior when
+node_modules is present, missing, npm is unavailable, or `npm install` fails.
+These tests monkeypatch subprocess and shutil.which so they don't need Node.
+"""
+from pathlib import Path
+
+import pytest
+
+from core import parser_adapter
+
+
+@pytest.fixture
+def fake_parser_dir(tmp_path, monkeypatch):
+    """Point _JS_PARSER_DIR at a tmp dir so tests don't touch the real one."""
+    monkeypatch.setattr(parser_adapter, "_JS_PARSER_DIR", tmp_path)
+    return tmp_path
+
+
+def test_skips_install_when_node_modules_present(fake_parser_dir, monkeypatch):
+    (fake_parser_dir / "node_modules").mkdir()
+
+    calls = []
+    monkeypatch.setattr(parser_adapter.subprocess, "run", lambda *a, **kw: calls.append((a, kw)))
+    monkeypatch.setattr(parser_adapter.shutil, "which", lambda name: "/usr/bin/npm")
+
+    parser_adapter._ensure_js_parser_dependencies()
+
+    assert calls == []
+
+
+def test_runs_npm_install_when_node_modules_missing(fake_parser_dir, monkeypatch):
+    calls = []
+
+    class _Ok:
+        returncode = 0
+
+    def _fake_run(cmd, **kwargs):
+        calls.append((cmd, kwargs))
+        return _Ok()
+
+    monkeypatch.setattr(parser_adapter.subprocess, "run", _fake_run)
+    monkeypatch.setattr(parser_adapter.shutil, "which", lambda name: "/usr/bin/npm")
+
+    parser_adapter._ensure_js_parser_dependencies()
+
+    assert len(calls) == 1
+    cmd, kwargs = calls[0]
+    assert cmd == ["/usr/bin/npm", "install"]
+    assert kwargs["cwd"] == str(fake_parser_dir)
+
+
+def test_raises_when_npm_not_on_path(fake_parser_dir, monkeypatch):
+    monkeypatch.setattr(parser_adapter.shutil, "which", lambda name: None)
+
+    with pytest.raises(RuntimeError, match="npm"):
+        parser_adapter._ensure_js_parser_dependencies()
+
+
+def test_raises_when_npm_install_fails(fake_parser_dir, monkeypatch):
+    class _Fail:
+        returncode = 1
+
+    monkeypatch.setattr(parser_adapter.subprocess, "run", lambda *a, **kw: _Fail())
+    monkeypatch.setattr(parser_adapter.shutil, "which", lambda name: "/usr/bin/npm")
+
+    with pytest.raises(RuntimeError, match="npm install.*exit code 1"):
+        parser_adapter._ensure_js_parser_dependencies()
+
+
+def test_parse_javascript_surfaces_bootstrap_error(fake_parser_dir, monkeypatch):
+    """When bootstrap fails, _parse_javascript must not run the Node subprocess."""
+    monkeypatch.setattr(parser_adapter.shutil, "which", lambda name: None)
+
+    ran_node = []
+    monkeypatch.setattr(
+        parser_adapter.subprocess,
+        "run",
+        lambda *a, **kw: ran_node.append((a, kw)),
+    )
+
+    with pytest.raises(RuntimeError, match="npm"):
+        parser_adapter._parse_javascript(
+            repo_path="/tmp/fake-repo",
+            output_dir="/tmp/fake-out",
+            processing_level="all",
+        )
+
+    assert ran_node == [], "Node subprocess should not run when bootstrap fails"