diff --git a/.github/workflows/publish.yml b/.github/workflows/publish.yml
index 3e229df..94cb58a 100644
--- a/.github/workflows/publish.yml
+++ b/.github/workflows/publish.yml
@@ -1,10 +1,12 @@
 name: Release
 
+# Formal releases are tag-only. Tags must be vX.Y.Z (stable) or a PEP 440
+# prerelease with a v prefix (e.g. v0.9.16a1). The package version in
+# pyproject.toml is the source of truth and must match the tag (without v).
 on:
   push:
     tags:
-      - "*"
-  workflow_dispatch:
+      - "v*"
 
 jobs:
   release-pypi:
@@ -22,39 +24,124 @@ jobs:
         with:
           enable-cache: "auto"
 
-      - name: Check prerelease
-        id: check_version
+      - name: Parse tag and verify package version
+        id: ver
         run: |
-          if [[ "${{ github.ref }}" =~ ^refs/tags/[0-9.]+$ ]]; then
-            echo "PRERELEASE=false" >> $GITHUB_OUTPUT
+          set -euo pipefail
+          TAG="${GITHUB_REF#refs/tags/}"
+
+          # Stable: v1.2.3
+          if [[ "$TAG" =~ ^v([0-9]+\.[0-9]+\.[0-9]+)$ ]]; then
+            TAG_VERSION="${BASH_REMATCH[1]}"
+            PRERELEASE=false
+          # Prerelease (PEP 440-ish): v1.2.3a1, v1.2.3b2, v1.2.3rc1, v1.2.3.dev0, …
+          elif [[ "$TAG" =~ ^v([0-9]+\.[0-9]+\.[0-9]+((a|b|rc|alpha|beta)[0-9]*|\.dev[0-9]+))$ ]]; then
+            TAG_VERSION="${BASH_REMATCH[1]}"
+            PRERELEASE=true
           else
-            echo "PRERELEASE=true" >> $GITHUB_OUTPUT
+            echo "Unsupported tag format: $TAG" >&2
+            echo "Expected vX.Y.Z or a PEP 440 prerelease with a v prefix (e.g. v0.9.16a1)." >&2
+            exit 1
+          fi
+
+          PKG_VERSION=$(python3 -c "import tomllib; print(tomllib.load(open('pyproject.toml', 'rb'))['project']['version'])")
+          if [[ "$PKG_VERSION" != "$TAG_VERSION" ]]; then
+            echo "Version mismatch: tag=$TAG_VERSION pyproject=$PKG_VERSION" >&2
+            echo "Bump pyproject.toml [project].version to match the tag before releasing." >&2
+            exit 1
           fi
 
+          {
+            echo "TAG_VERSION=$TAG_VERSION"
+            echo "PRERELEASE=$PRERELEASE"
+          } >> "$GITHUB_OUTPUT"
+          echo "tag=$TAG version=$TAG_VERSION prerelease=$PRERELEASE"
+
       - name: Build package
         run: uv build
 
+      - name: Assert dist version matches tag
+        run: |
+          set -euo pipefail
+          TAG_VERSION="${{ steps.ver.outputs.TAG_VERSION }}"
+          shopt -s nullglob
+          wheels=(dist/*.whl)
+          sdists=(dist/*.tar.gz)
+          if [[ ${#wheels[@]} -eq 0 ]]; then
+            echo "No wheel found under dist/" >&2
+            exit 1
+          fi
+          for path in "${wheels[@]}"; do
+            base=$(basename "$path")
+            if [[ ! "$base" =~ ^fit_tool-(.+)-py[0-9]+-none-any\.whl$ ]]; then
+              echo "Unexpected wheel name: $base" >&2
+              exit 1
+            fi
+            if [[ "${BASH_REMATCH[1]}" != "$TAG_VERSION" ]]; then
+              echo "Wheel version ${BASH_REMATCH[1]} != tag version $TAG_VERSION" >&2
+              exit 1
+            fi
+          done
+          for path in "${sdists[@]}"; do
+            base=$(basename "$path")
+            if [[ ! "$base" =~ ^fit[_-]tool-(.+)\.tar\.gz$ ]]; then
+              echo "Unexpected sdist name: $base" >&2
+              exit 1
+            fi
+            if [[ "${BASH_REMATCH[1]}" != "$TAG_VERSION" ]]; then
+              echo "Sdist version ${BASH_REMATCH[1]} != tag version $TAG_VERSION" >&2
+              exit 1
+            fi
+          done
+
+      - name: Extract changelog for this version
+        run: |
+          set -euo pipefail
+          TAG_VERSION="${{ steps.ver.outputs.TAG_VERSION }}"
+          # Match Towncrier headers exactly: "## Release v{version} ({date})".
+          # Require a space after the version so v0.9.1 does not match v0.9.15.
+          awk -v ver="$TAG_VERSION" '
+            $0 ~ ("^## Release v" ver " ") {
+              if (found) exit
+              found = 1
+              print
+              next
+            }
+            /^## Release/ && found { exit }
+            found { print }
+          ' CHANGELOG.md > .changelog.md
+
+          if ! grep -Eq "^## Release v${TAG_VERSION} " .changelog.md; then
+            echo "CHANGELOG.md has no section header matching '## Release v${TAG_VERSION} …'" >&2
+            echo "Run: uv run towncrier build --version ${TAG_VERSION}" >&2
+            exit 1
+          fi
+          if [[ ! -s .changelog.md ]]; then
+            echo "Extracted changelog is empty" >&2
+            exit 1
+          fi
+
       - name: Upload artifacts
         uses: actions/upload-artifact@v7.0.1
         with:
           name: fit-tool-wheel
-          path: dist/*.whl
+          path: |
+            dist/*.whl
+            dist/*.tar.gz
           if-no-files-found: error
           retention-days: 15
 
+      # Publish only after version + changelog gates pass so a missing
+      # Towncrier section never leaves an orphan PyPI upload.
       - name: Publish to PyPI
         uses: pypa/gh-action-pypi-publish@release/v1
 
-      - name: Get Changelog
-        id: get-changelog
-        run: |
-          awk '/## Release/{if (flag==1)exit;else;flag=1;next} flag' CHANGELOG.md > .changelog.md
-
-      - name: Create Release
+      - name: Create GitHub Release
         uses: softprops/action-gh-release@v3
         with:
+          tag_name: ${{ github.ref_name }}
           body_path: .changelog.md
           draft: false
-          prerelease: ${{ steps.check_version.outputs.PRERELEASE }}
+          prerelease: ${{ steps.ver.outputs.PRERELEASE }}
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
diff --git a/AGENTS.md b/AGENTS.md
index e8702f3..f55f7c4 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -17,6 +17,7 @@ The project uses setuptools through `pyproject.toml`, `uv` for dependency and lo
 - `fit_tool/profile/profile_type.py` and `fit_tool/profile/messages/`: generated profile code.
 - `news/`: Towncrier fragments named `<issue>.<type>`.
 - `.github/workflows/`: CI and PyPI release workflows.
+- `docs/RELEASING.md`: maintainer checklist for tagging and publishing a new version.
 
 ## Setup and common commands
 
@@ -139,6 +140,12 @@ Write fragments as concise, user-facing descriptions. Do not edit a released sec
 
 Update `README.md` when installation, CLI usage, supported workflows, or runnable examples change. Keep packaging metadata and console entry points in `pyproject.toml` aligned with the code and documentation.
 
+## Releasing
+
+Package version is static in `pyproject.toml` (`[project].version`). Git tags use a `v` prefix (`v0.9.15`) and must match that version (without `v`). Pushing a matching `v*` tag runs the Release workflow (PyPI via Trusted Publishing + GitHub Release from `CHANGELOG.md`).
+
+Full checklist, tag rules, and failure notes: [`docs/RELEASING.md`](docs/RELEASING.md).
+
 ## Change discipline
 
 - Keep changes focused and preserve unrelated user modifications in the working tree.
diff --git a/README.md b/README.md
index a35a994..ef5c02c 100644
--- a/README.md
+++ b/README.md
@@ -175,4 +175,5 @@ uv run python fit_tool/examples/write_workout_example.py
 | [`docs/CAPABILITY_BOUNDARY.md`](docs/CAPABILITY_BOUNDARY.md) | Supported / partial / incomplete matrix; validation & encode details |
 | [`docs/FIT_CONFORMANCE_DESIGN.md`](docs/FIT_CONFORMANCE_DESIGN.md) | Target architecture and roadmap |
 | [`docs/EPIC_SHA12_RELEASE_NOTES.md`](docs/EPIC_SHA12_RELEASE_NOTES.md) | Protocol-capability epic rollup notes |
+| [`docs/RELEASING.md`](docs/RELEASING.md) | Maintainer checklist for PyPI / GitHub releases |
 | [`fit_tool/tests/data/README.md`](fit_tool/tests/data/README.md) | Fixture inventory and gap map |
diff --git a/docs/RELEASING.md b/docs/RELEASING.md
new file mode 100644
index 0000000..638d53d
--- /dev/null
+++ b/docs/RELEASING.md
@@ -0,0 +1,74 @@
+# Releasing `fit-tool`
+
+This document is the checklist for publishing a new version to PyPI and GitHub
+Releases. Day-to-day contribution rules live in [`AGENTS.md`](../AGENTS.md).
+
+## How release works
+
+| Piece | Role |
+| --- | --- |
+| `pyproject.toml` → `[project].version` | **Source of truth** for the package version (wheel / sdist / PyPI) |
+| Git tag `vX.Y.Z` | Triggers [`.github/workflows/publish.yml`](../.github/workflows/publish.yml) |
+| `news/*` + Towncrier | Builds the new section in `CHANGELOG.md` |
+| PyPI | Trusted Publishing (OIDC); no long-lived API token in the repo |
+| GitHub Release | Created by the same workflow; body = the matching `CHANGELOG.md` section |
+
+The workflow **does not** rewrite the package version from the tag. It only
+checks that they match. If they differ, the job fails before publish.
+
+**Tag rules**
+
+- Stable: `v0.9.16` (must match `version = "0.9.16"` in `pyproject.toml`)
+- Prerelease: `v0.9.16a1`, `v0.9.16rc1`, `v0.9.16.dev0` (same string without `v` in `pyproject.toml`)
+- Do not use bare `0.9.16` or legacy `version/0.9.x` tags for new releases
+
+## Checklist
+
+1. **`main` is green** — CI (Python 3.9–3.14 + Garmin JS interop) passes on the commit you will tag.
+2. **News fragments are ready** — user-visible changes have `news/<id>.<type>` files (see `AGENTS.md`). Do not hand-edit an already-released section of `CHANGELOG.md`.
+3. **Choose the version** — e.g. `0.9.16` (patch) or `0.10.0` (broader capability signal). PyPI will not accept re-uploading an existing version.
+4. **Bump the package version** in `pyproject.toml`:
+   ```toml
+   version = "0.9.16"
+   ```
+5. **Build the changelog**:
+   ```bash
+   uv run towncrier build --version 0.9.16
+   # optional dry-run first:
+   uv run towncrier build --version 0.9.16 --draft
+   ```
+   This prepends `## Release v0.9.16 (YYYY-MM-DD)` to `CHANGELOG.md` and removes consumed `news/*` fragments (keep `news/.gitkeep`).
+6. **Review** the new `CHANGELOG.md` section and the diff (version + changelog + deleted news files only, unless the release intentionally includes other commits already on `main`).
+7. **Commit and merge to `main`** (via PR if that is your normal process).
+8. **Tag and push the tag** on the release commit:
+   ```bash
+   git checkout main
+   git pull
+   git tag v0.9.16
+   git push origin v0.9.16
+   ```
+9. **Watch** Actions → workflow **Release**. Expect: version gate → `uv build` → dist version check → **changelog section gate** → PyPI publish → GitHub Release with changelog body and `prerelease=false` for stable tags. (Changelog is validated *before* PyPI so a missing Towncrier section cannot leave an orphan upload.)
+10. **Verify**:
+    - https://pypi.org/project/fit-tool/ shows the new version
+    - `pip install fit-tool==X.Y.Z` (or `uv add fit-tool==X.Y.Z`) works
+    - GitHub Release page body matches the changelog section and is not marked Pre-release for stable tags
+
+## What the workflow rejects
+
+- Tags that are not `v…`
+- Tag version ≠ `pyproject.toml` version
+- Built wheel/sdist version ≠ tag version
+- Missing `## Release vX.Y.Z` section in `CHANGELOG.md`
+- Empty extracted changelog body
+
+## Failure notes
+
+- **PyPI succeeded, GitHub Release failed**: do **not** re-run the whole job blindly (PyPI will reject the same files). Create or edit the GitHub Release for that tag and paste the matching changelog section, or fix the Release step and re-run only that step if the workflow is later split.
+- **Version already on PyPI**: bump to a new version; never try to overwrite.
+- **Never** push a release tag or publish to PyPI from an automated agent unless a human explicitly requested that release.
+
+## Related docs
+
+- [`AGENTS.md`](../AGENTS.md) — news fragment types and agent constraints
+- [`CHANGELOG.md`](../CHANGELOG.md) — published history
+- [`EPIC_SHA12_RELEASE_NOTES.md`](EPIC_SHA12_RELEASE_NOTES.md) — narrative rollup for the protocol epic (not a substitute for Towncrier)
diff --git a/news/SHA-36.doc b/news/SHA-36.doc
new file mode 100644
index 0000000..1ac1015
--- /dev/null
+++ b/news/SHA-36.doc
@@ -0,0 +1 @@
+Document the release checklist and harden the tag-based PyPI/GitHub Release workflow (version gate, ``v``-prefix tags, changelog extraction).