diff --git a/scripts/update_changelog.sh b/scripts/update_changelog.sh
index 2889e41..a9a2998 100644
--- a/scripts/update_changelog.sh
+++ b/scripts/update_changelog.sh
@@ -1,9 +1,33 @@
 #!/usr/bin/env bash
-set -euo pipefail
+# -----------------------------------------------------------------------------
 
-# scripts/update_changelog.sh
+# Copyright (C) 2025 Moko Consulting <hello@mokoconsulting.tech>
 #
-# Purpose:
+# This file is part of a Moko Consulting project.
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# This program is free software; you can redistribute it and/or modify it under
+# the terms of the GNU General Public License as published by the Free Software
+# Foundation; either version 3 of the License, or (at your option) any later
+# version.
+#
+# This program is distributed in the hope that it will be useful, but WITHOUT
+# ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+# FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License (./LICENSE.md).
+# -----------------------------------------------------------------------------
+
+# FILE INFORMATION
+# DEFGROUP: MokoStandards
+# INGROUP: Generic.Script
+# REPO: https://github.com/mokoconsulting-tech/MokoDefaults
+# PATH: /scripts/update_changelog.sh
+# VERSION: 01.00.00
+# BRIEF: Insert a versioned CHANGELOG.md entry immediately after the main Changelog heading.
+# NOTES
+# # Purpose:
 # - Apply the MokoWaaS-Brand CHANGELOG template entry for a given version.
 # - Insert a new header at the top of CHANGELOG.md, immediately after "# Changelog".
 # - Avoid duplicates if an entry for the version already exists.
@@ -14,67 +38,87 @@ set -euo pipefail
 #
 # Example:
 #   ./scripts/update_changelog.sh 01.05.00
+# =============================================================================
 
-VERSION="${1:-}"
-
-if [[ -z "${VERSION}" ]]; then
-  echo "ERROR: Version argument is required. Usage: scripts/update_changelog.sh <VERSION>" >&2
-  exit 1
-fi
+set -euo pipefail
 
 CHANGELOG_FILE="CHANGELOG.md"
 
-DATE_UTC="$(date -u +"%Y-%m-%d")"
-HEADER="## ${VERSION} - ${DATE_UTC}"
+die() {
+  echo "ERROR: $*" 1>&2
+  exit 1
+}
 
-if [[ ! -f "${CHANGELOG_FILE}" ]]; then
-  {
-    echo "# Changelog"
-    echo
-  } > "${CHANGELOG_FILE}"
-fi
+info() {
+  echo "INFO: $*"
+}
 
-# Do not duplicate existing entries
-if grep -qE "^##[[:space:]]+${VERSION}[[:space:]]+-[[:space:]]+" "${CHANGELOG_FILE}"; then
-  echo "CHANGELOG.md already contains an entry for ${VERSION}. No changes made."
-  exit 0
-fi
+require_cmd() {
+  command -v "$1" >/dev/null 2>&1 || die "Missing required command: $1"
+}
 
-TMP_FILE="${CHANGELOG_FILE}.tmp"
+validate_version() {
+  local v="$1"
+  [[ "$v" =~ ^[0-9]{2}\.[0-9]{2}\.[0-9]{2}$ ]] || die "Invalid version '$v'. Expected NN.NN.NN (example 03.01.00)."
+}
 
-# Insert after the first '# Changelog' line.
-# If '# Changelog' is missing, prepend it.
-if grep -qE "^# Changelog$" "${CHANGELOG_FILE}"; then
-  awk -v header="${HEADER}" '
+main() {
+  require_cmd awk
+  require_cmd grep
+  require_cmd mktemp
+  require_cmd date
+
+  [[ $# -eq 1 ]] || die "Usage: $0 <VERSION>"
+  local version="$1"
+  validate_version "$version"
+
+  [[ -f "$CHANGELOG_FILE" ]] || die "Missing $CHANGELOG_FILE in repo root."
+
+  if ! grep -qE '^# Changelog[[:space:]]*$' "$CHANGELOG_FILE"; then
+    die "$CHANGELOG_FILE must contain a top level heading exactly: # Changelog"
+  fi
+
+  if grep -qE "^## \[$version\][[:space:]]" "$CHANGELOG_FILE"; then
+    info "CHANGELOG.md already contains an entry for version $version. No action taken."
+    exit 0
+  fi
+
+  local stamp
+  stamp="$(date '+%Y-%m-%d')"
+
+  local tmp
+  tmp="$(mktemp)"
+  trap 'rm -f "$tmp"' EXIT
+
+  awk -v v="$version" -v d="$stamp" '
     BEGIN { inserted=0 }
     {
-      print
-      if (!inserted && $0 ~ /^# Changelog$/) {
-        print ""
-        print header
-        print ""
-        inserted=1
-      }
+	print $0
+	if (inserted==0 && $0 ~ /^# Changelog[[:space:]]*$/) {
+	  print ""
+	  print "## [" v "] " d
+	  print "- Version bump."
+	  print ""
+	  inserted=1
+	}
     }
     END {
-      if (!inserted) {
-        # fallback: append at end
-        print ""
-        print header
-        print ""
-      }
+	if (inserted==0) {
+	  exit 3
+	}
     }
-  ' "${CHANGELOG_FILE}" > "${TMP_FILE}"
-else
-  {
-    echo "# Changelog"
-    echo
-    echo "${HEADER}"
-    echo
-    cat "${CHANGELOG_FILE}"
-  } > "${TMP_FILE}"
-fi
+  ' "$CHANGELOG_FILE" > "$tmp" || {
+    rc=$?
+    if [[ $rc -eq 3 ]]; then
+	die "Insertion point not found. Expected: # Changelog"
+    fi
+    die "Failed to update $CHANGELOG_FILE (awk exit code $rc)."
+  }
 
-mv "${TMP_FILE}" "${CHANGELOG_FILE}"
+  mv "$tmp" "$CHANGELOG_FILE"
+  trap - EXIT
 
-echo "Applied changelog header: ${HEADER}"
+  info "Inserted CHANGELOG.md entry for version $version on $stamp."
+}
+
+main "$@"