diff --git a/.github/workflows/release-builtins.yml b/.github/workflows/release-builtins.yml
index 408f9c7..538ef90 100644
--- a/.github/workflows/release-builtins.yml
+++ b/.github/workflows/release-builtins.yml
@@ -20,30 +20,56 @@ jobs:
   build:
     name: Build distribution
     runs-on: ubuntu-latest
-
+    outputs:
+      release: ${{ steps.check.outputs.release }}
     steps:
     - uses: actions/checkout@v4
       with:
         submodules: true
         fetch-depth: 0
         persist-credentials: false
-    - name: update core
-      env:
-        TAG: ${{ inputs.tag || 'origin/master' }}
-      # needs to detach because we can update to a tag
-      run: git -C uap-core switch --detach "$TAG"
     - name: Set up Python
       uses: actions/setup-python@v5
       with:
         python-version: "3.x"
 
+    - name: Check necessity of release
+      id: check
+      env:
+        PYPI: ${{ github.event.inputs.environment }}
+        REF: ${{ inputs.tag || 'HEAD' }}
+      run: |
+        case $PYPI in
+            pypi)
+                DOMAIN=pypi.org
+                ;;
+            testpypi)
+                DOMAIN=test.pypi.org
+                ;;
+            *)
+                exit 1
+        esac
+
+        RELREV=$(python scripts/relrev.py --domain "$DOMAIN")
+        VERSION=$(date +%Y%m)
+        CURREV=$(python scripts/tagcore.py --ref $REF --version $VERSION)
+
+        if [ -n "$CURREV" -a "$RELREV" = "$CURREV" ]
+        then
+            echo "current rev matches latest release, skip new release"
+        else
+            echo release=true >> $GITHUB_OUTPUT
+        fi
     - name: Install pypa/build
+      if: ${{ steps.check.outputs.release == 'true' }}
       run: python3 -m pip install build --user
     - name: Build wheel
+      if: ${{ steps.check.outputs.release == 'true' }}
       run: |
         python3 -m build -w ua-parser-builtins
         mv ua-parser-builtins/dist .
     - name: Store the distribution packages
+      if: ${{ steps.check.outputs.release == 'true' }}
       uses: actions/upload-artifact@v4
       with:
         name: python-package-distributions
@@ -51,9 +77,8 @@ jobs:
 
   publish-to-testpypi:
     name: Publish to TestPyPI
-    if: ${{ github.event.inputs.environment == 'testpypi' }}
-    needs:
-    - build
+    needs: build
+    if: ${{ github.event.inputs.environment == 'testpypi' && needs.build.outputs.release == 'true' }}
     runs-on: ubuntu-latest
 
     environment:
@@ -78,9 +103,8 @@ jobs:
 
   publish-to-pypi:
     name: publish
-    if: ${{ github.event_name == 'schedule' || github.event.inputs.environment == 'pypi' }}
-    needs:
-    - build
+    needs: build
+    if: ${{ (github.event_name == 'schedule' || github.event.inputs.environment == 'pypi') && needs.build.outputs.release == 'true' }}
     runs-on: ubuntu-latest
     environment:
       name: pypi
diff --git a/scripts/relrev.py b/scripts/relrev.py
new file mode 100644
index 0000000..0979a40
--- /dev/null
+++ b/scripts/relrev.py
@@ -0,0 +1,67 @@
+import argparse
+import contextlib
+import hashlib
+import json
+import re
+import shutil
+import sys
+import tempfile
+import zipfile
+from urllib import parse, request
+
+parser = argparse.ArgumentParser(
+    description="Retrieves the revision for the latest release of ua-parser-builtins",
+)
+parser.add_argument(
+    "--domain",
+    default="pypi.org",
+)
+args = parser.parse_args()
+
+url = parse.urlunsplit(("https", args.domain, "simple/ua-parser-builtins", "", ""))
+
+print("checking", url, file=sys.stderr)
+res = request.urlopen(
+    request.Request(
+        url,
+        headers={
+            "Accept": "application/vnd.pypi.simple.v1+json",
+        },
+    )
+)
+if res.status != 200:
+    exit(f"Failed to retrieve project distributions: {res.status}")
+
+distributions = json.load(res)
+version, distribution = next(
+    (v, d)
+    for v, d in zip(
+        reversed(distributions["versions"]), reversed(distributions["files"])
+    )
+    if not d["yanked"]
+    if re.fullmatch(
+        r"(\d+!)?\d+(\.\d+)*(\.post\d+)?",
+        v,
+        flags=re.ASCII,
+    )
+)
+print("latest version:", version, file=sys.stderr)
+
+res = request.urlopen(distribution["url"])
+if res.status != 200:
+    exit(f"Failed to retrieve wheel: {res.status}")
+
+with tempfile.SpooledTemporaryFile(256 * 1024) as tf:
+    shutil.copyfileobj(res, tf)
+    for name, val in distribution["hashes"].items():
+        tf.seek(0)
+        d = hashlib.file_digest(tf, name).hexdigest()
+        if d != val:
+            exit(f"{name} mismatch: expected {val!r} got {d!r}")
+    tf.seek(0)
+    with zipfile.ZipFile(tf) as z:
+        # if the REVISION file is not found then it's fine it's a
+        # pre-calver release (hopefully) and that means we should cut
+        # a calver one
+        with contextlib.suppress(KeyError):
+            print(z.read("REVISION").decode())
diff --git a/scripts/tagcore.py b/scripts/tagcore.py
new file mode 100644
index 0000000..a5ef7f8
--- /dev/null
+++ b/scripts/tagcore.py
@@ -0,0 +1,72 @@
+import argparse
+import datetime
+import pathlib
+import shutil
+import subprocess
+
+CORE_REMOTE = "https://github.com/ua-parser/uap-core"
+
+
+parser = argparse.ArgumentParser(
+    description="""Updates `uap-core` to `ref` and tags it with `version`
+
+If successful, writes the commit to `REVISION` and prints it to stdout.
+"""
+)
+parser.add_argument(
+    "--ref",
+    default="HEAD",
+    help="uap-core ref to build, defaults to HEAD (the head of the default branch)",
+)
+parser.add_argument(
+    "--version",
+    help="version to tag the package as, defaults to an YMD calendar version matching the ref's commit date",
+)
+args = parser.parse_args()
+
+
+if not shutil.which("git"):
+    exit("git required")
+
+r = subprocess.run(
+    ["git", "ls-remote", CORE_REMOTE, args.ref],
+    encoding="utf-8",
+    stdout=subprocess.PIPE,
+)
+if r.returncode:
+    exit("Unable to query uap-core repo")
+
+if r.stdout:
+    if r.stdout.count("\n") > 1:
+        exit(f"Found multiple matching refs for {args.ref}:\n{r.stdout}")
+    commit, _rest = r.stdout.split("\t", 1)
+else:
+    try:
+        int(args.ref, 16)
+        commit = args.ref
+    except ValueError:
+        exit(f"Unknown or invalid ref {args.ref!r}")
+
+CORE_PATH = pathlib.Path(__file__).resolve().parent.parent / "uap-core"
+
+r = subprocess.run(["git", "-C", CORE_PATH, "fetch", CORE_REMOTE, commit])
+if r.returncode:
+    exit(f"Unable to retrieve commit {commit!r}")
+
+if args.version:
+    tagname = args.version
+else:
+    r = subprocess.run(
+        ["git", "-C", CORE_PATH, "show", "-s", "--format=%cs", commit],
+        encoding="utf-8",
+        stdout=subprocess.PIPE,
+    )
+    if r.returncode or not r.stdout:
+        exit(f"Unable to retrieve commit date from commit {commit!r}")
+
+    tagname = datetime.date.fromisoformat(r.stdout.rstrip()).strftime("%Y%m%d")
+
+subprocess.run(["git", "-C", CORE_PATH, "switch", "-d", commit])
+subprocess.run(["git", "-C", CORE_PATH, "tag", tagname, commit])
+CORE_PATH.joinpath("REVISION").write_text(commit)
+print(commit)
diff --git a/ua-parser-builtins/hatch_build.py b/ua-parser-builtins/hatch_build.py
index 9bbe23f..2a86012 100644
--- a/ua-parser-builtins/hatch_build.py
+++ b/ua-parser-builtins/hatch_build.py
@@ -41,6 +41,10 @@ def initialize(
         version: str,
         build_data: dict[str, Any],
     ) -> None:
+        rev = os.path.join(self.root, "uap-core/REVISION")
+        if os.path.exists(rev):
+            build_data["force_include"][rev] = "REVISION"
+
         with open(os.path.join(self.root, "uap-core/regexes.yaml"), "rb") as f:
             data = yaml.safe_load(f)