diff --git a/Makefile b/Makefile
index 0c01658..3e4341d 100644
--- a/Makefile
+++ b/Makefile
@@ -33,6 +33,7 @@ release: dist
 	uv publish
 
 release-npm: clean build
+	uv run python scripts/set_npm_version.py
 	cd js && npm publish
 
 add-language:
diff --git a/js/package.json b/js/package.json
index 4c27540..d6fa0f4 100644
--- a/js/package.json
+++ b/js/package.json
@@ -27,5 +27,5 @@
   "scripts": {
     "test": "echo \"Error: no test specified\" && exit 1"
   },
-  "version": "0.2.18"
+  "version": "0.0.0"
 }
diff --git a/scripts/generate_from_specs.py b/scripts/generate_from_specs.py
index 598daa1..66c8d62 100644
--- a/scripts/generate_from_specs.py
+++ b/scripts/generate_from_specs.py
@@ -14,7 +14,6 @@
 from collections import OrderedDict
 from glob import glob
 from hashlib import md5
-from importlib.metadata import version as get_version
 from uuid import UUID
 from uuid import uuid3
 
@@ -259,43 +258,6 @@ def write_constants_src_files(constants_outputs, schemas):
     return output_files
 
 
-def pep440_to_npm_semver(version):
-    """Convert a PEP 440 version to npm-compatible semver.
-
-    Extracts just the base version (X.Y.Z) to ensure the version is
-    stable across commits and valid npm semver. Dev/local suffixes from
-    setuptools-scm change with every commit, which would cause the
-    rebuild-from-specs pre-commit hook to perpetually modify this file.
-    On tagged releases, setuptools-scm returns the clean version directly.
-    """
-    match = re.match(r"(\d+\.\d+\.\d+)", version)
-    return match.group(1) if match else version
-
-
-def set_package_json_version():
-    python_version = get_version("le-utils")
-    npm_version = pep440_to_npm_semver(python_version)
-
-    package_json = os.path.join(js_output_dir, "package.json")
-
-    with open(package_json, "r") as f:
-        package = json.load(f)
-
-    package["version"] = npm_version
-
-    with open(package_json, "w") as f:
-        output = json.dumps(package, indent=2, sort_keys=True)
-        firstline = True
-        for line in output.split("\n"):
-            if firstline:
-                firstline = False
-            else:
-                f.write("\n")
-            f.write(line.rstrip())
-        f.write("\n")
-    return [package_json]
-
-
 if __name__ == "__main__":
     labels_to_write = read_labels_specs()
 
@@ -310,8 +272,6 @@ def set_package_json_version():
 
     output_files += write_constants_src_files(constants_to_write, schemas_to_write)
 
-    output_files += set_package_json_version()
-
     py_files = [f for f in output_files if f.endswith(".py")]
     subprocess.call(["ruff", "check", "--fix"] + py_files)
     subprocess.call(["ruff", "format"] + py_files)
diff --git a/scripts/set_npm_version.py b/scripts/set_npm_version.py
new file mode 100644
index 0000000..1f78cba
--- /dev/null
+++ b/scripts/set_npm_version.py
@@ -0,0 +1,55 @@
+"""
+set_npm_version
+Writes the release version into js/package.json, for the npm publish path only.
+
+Kept out of generate_from_specs.py on purpose. The version is derived from git
+tags, so a tracked value can never match what setuptools-scm computes once a
+release tag is created: the tag is applied to a commit whose package.json was
+written before the tag existed. Regenerating it as part of `make build` made the
+rebuild-from-specs hook fail on every commit after a release. The tracked value
+is a 0.0.0 placeholder; only `make release-npm` sets a real one.
+"""
+
+import json
+import os
+import re
+from importlib.metadata import version as get_version
+
+package_json = os.path.join(os.path.dirname(__file__), "..", "js", "package.json")
+
+
+def pep440_to_npm_semver(version):
+    """Return version if it is an exact X.Y.Z release, else fail.
+
+    setuptools-scm only returns a bare X.Y.Z for a checkout at a release tag.
+    Anything else carries a dev/local suffix and would publish a version that
+    does not correspond to a release.
+    """
+    if not re.match(r"^\d+\.\d+\.\d+$", version):
+        raise SystemExit("Refusing to set npm version from non-release version {!r}. Publish from a checkout at a release tag.".format(version))
+    return version
+
+
+def set_package_json_version():
+    npm_version = pep440_to_npm_semver(get_version("le-utils"))
+
+    with open(package_json, "r") as f:
+        package = json.load(f)
+
+    package["version"] = npm_version
+
+    with open(package_json, "w") as f:
+        output = json.dumps(package, indent=2, sort_keys=True)
+        firstline = True
+        for line in output.split("\n"):
+            if firstline:
+                firstline = False
+            else:
+                f.write("\n")
+            f.write(line.rstrip())
+        f.write("\n")
+    return npm_version
+
+
+if __name__ == "__main__":
+    print("Set js/package.json version to {}".format(set_package_json_version()))