diff --git a/.cspell.json b/.cspell.json
index cf80ea0..572cd22 100644
--- a/.cspell.json
+++ b/.cspell.json
@@ -38,7 +38,10 @@
     "nixpkgs",
     "Anson",
     "pipefail",
-    "mikefarah"
+    "mikefarah",
+    "kislyuk",
+    "gsub",
+    "RLENGTH"
   ],
   "ignorePaths": [
     ".git",
diff --git a/.file-size.yml b/.file-size.yml
new file mode 100644
index 0000000..d1fae20
--- /dev/null
+++ b/.file-size.yml
@@ -0,0 +1,35 @@
+# =============================================================================
+# Org-wide File Size Limits
+# =============================================================================
+# Per-repo overrides: create .file-size.yml in the repo root.
+# Sizes are in bytes.
+# =============================================================================
+
+defaults:
+  warn: 5120      # 5 KB
+  error: 10240    # 10 KB
+
+extended:
+  warn: 10240     # 10 KB
+  error: 20480    # 20 KB
+  files:
+    - CHANGELOG.md
+    - CONTRIBUTING.md
+    - LABELS.md
+    - README.md
+    - repo-health-audit-prompt.md
+
+exempt:
+  - "*.lock"
+  - "package-lock.json"
+  - "pnpm-lock.yaml"
+
+scan:
+  - .nix
+  - .md
+  - .sh
+  - .yml
+  - .yaml
+  - .tf
+  - .py
+  - .j2
diff --git a/.github/workflows/_file-size.yml b/.github/workflows/_file-size.yml
index 55b76c8..86da7c4 100644
--- a/.github/workflows/_file-size.yml
+++ b/.github/workflows/_file-size.yml
@@ -1,12 +1,12 @@
 # Reusable: File Size Check
-# Delegates to repo's own script if available, otherwise runs inline check.
+# Delegates to repo's own script, shared YAML-config checker, or inline fallback.
 name: _file-size
 
 on:
   workflow_call:
     inputs:
       max-file-size-kb:
-        description: "Maximum file size in KB"
+        description: "Maximum file size in KB (legacy fallback)"
         type: number
         default: 500
       exclude-patterns:
@@ -32,11 +32,23 @@ jobs:
         env:
           MAX_KB: ${{ inputs.max-file-size-kb }}
           EXCLUDES: ${{ inputs.exclude-patterns }}
+          REPO_OWNER: ${{ github.repository_owner }}
         run: |
-          # Delegate to repo script if available
+          # Priority 1: Delegate to repo's own script
           [ -x "./scripts/workflows/check-file-sizes.sh" ] && exec ./scripts/workflows/check-file-sizes.sh
 
-          # Build find exclusions from JSON input
+          # Priority 2: Use shared YAML-config checker if .file-size.yml exists
+          if [ -f ".file-size.yml" ]; then
+            if curl -sSfL --retry 3 --retry-connrefused \
+              "https://raw.githubusercontent.com/${REPO_OWNER}/.github/main/scripts/workflows/check-file-sizes.sh" \
+              -o /tmp/check-file-sizes.sh; then
+              chmod +x /tmp/check-file-sizes.sh
+              exec /tmp/check-file-sizes.sh
+            fi
+            echo "::warning::Failed to download shared checker; falling back to inline"
+          fi
+
+          # Priority 3: Inline fallback (legacy)
           args=()
           for p in $(echo "$EXCLUDES" | jq -r '.[]'); do
             [[ "$p" == */* ]] && args+=(-not -path "$p") || args+=(-not -name "$p")
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index be529ce..6190976 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -74,3 +74,16 @@ repos:
       - id: check-branch
         name: Check branch naming conventions
         stages: [pre-push]
+
+  # ---------------------------------------------------------------------------
+  # File size enforcement
+  # ---------------------------------------------------------------------------
+  - repo: local
+    hooks:
+      - id: file-size-check
+        name: Check file sizes
+        entry: scripts/workflows/check-file-sizes.sh
+        language: script
+        always_run: true
+        pass_filenames: false
+        stages: [pre-commit]
diff --git a/scripts/workflows/check-file-sizes.sh b/scripts/workflows/check-file-sizes.sh
new file mode 100755
index 0000000..93f9810
--- /dev/null
+++ b/scripts/workflows/check-file-sizes.sh
@@ -0,0 +1,155 @@
+#!/usr/bin/env bash
+# =============================================================================
+# File Size Checker
+# =============================================================================
+# Checks file sizes against YAML config (.file-size.yml).
+# Requires yq (Go mikefarah/yq or Python kislyuk/yq).
+# Outputs GitHub Actions annotations in CI, plain text otherwise.
+# Exit code = number of error-level violations (capped at 125).
+# =============================================================================
+set -euo pipefail
+
+# ---------------------------------------------------------------------------
+# Defaults (used when no config file is present)
+# ---------------------------------------------------------------------------
+DEFAULT_WARN=5120
+DEFAULT_ERROR=10240
+DEFAULT_SCAN=(.nix .md .sh .yml .yaml .tf .py .j2)
+EXTENDED_WARN=""
+EXTENDED_ERROR=""
+declare -a EXTENDED_FILES=()
+declare -a EXEMPT_PATTERNS=()
+declare -a SCAN_EXTENSIONS=()
+
+# Resolve CI mode once at startup
+CI_MODE=false
+[[ -n "${GITHUB_ACTIONS:-}" ]] && CI_MODE=true
+
+# ---------------------------------------------------------------------------
+# Helpers
+# ---------------------------------------------------------------------------
+emit() {
+  local level="$1" file="$2" msg="$3"
+  if $CI_MODE; then
+    echo "::${level} file=${file}::${msg}"
+  else
+    echo "${level^^}: ${file}: ${msg}"
+  fi
+}
+
+# Populate a global array from a command's line-by-line output
+# Usage: read_into ARRAY_NAME command args...
+read_into() {
+  local -n _arr=$1; shift
+  while IFS= read -r line; do
+    [[ -n "$line" ]] && _arr+=("$line")
+  done < <("$@")
+}
+
+# Check if a basename matches any entry in a named array (glob matching)
+# Usage: matches_list ARRAY_NAME "$file"
+matches_list() {
+  local -n _list=$1
+  local bn
+  bn=$(basename "$2")
+  for pattern in "${_list[@]}"; do
+    # shellcheck disable=SC2254
+    case "$bn" in $pattern) return 0 ;; esac
+  done
+  return 1
+}
+
+# ---------------------------------------------------------------------------
+# Parse config (requires yq)
+# ---------------------------------------------------------------------------
+parse_config() {
+  local config="$1"
+
+  if ! command -v yq &>/dev/null; then
+    echo "ERROR: yq is required to parse ${config}" >&2
+    return 1
+  fi
+
+  if ! yq '.' "$config" &>/dev/null; then
+    echo "ERROR: yq failed to parse ${config}" >&2
+    return 1
+  fi
+
+  DEFAULT_WARN=$(yq -r '.defaults.warn // empty' "$config")
+  DEFAULT_ERROR=$(yq -r '.defaults.error // empty' "$config")
+  EXTENDED_WARN=$(yq -r '.extended.warn // empty' "$config")
+  EXTENDED_ERROR=$(yq -r '.extended.error // empty' "$config")
+
+  read_into EXTENDED_FILES yq -r '.extended.files // [] | .[]' "$config"
+  read_into EXEMPT_PATTERNS yq -r '.exempt // [] | .[]' "$config"
+  read_into SCAN_EXTENSIONS yq -r '.scan // [] | .[]' "$config"
+
+  : "${DEFAULT_WARN:=5120}"
+  : "${DEFAULT_ERROR:=10240}"
+}
+
+# ---------------------------------------------------------------------------
+# Main
+# ---------------------------------------------------------------------------
+main() {
+  local config_file=".file-size.yml"
+
+  if [[ -f "$config_file" ]]; then
+    parse_config "$config_file" || exit 1
+  fi
+
+  if [[ ${#SCAN_EXTENSIONS[@]} -eq 0 ]]; then
+    SCAN_EXTENSIONS=("${DEFAULT_SCAN[@]}")
+  fi
+
+  # Build find name predicates
+  local name_args=() first=true
+  for ext in "${SCAN_EXTENSIONS[@]}"; do
+    $first && first=false || name_args+=(-o)
+    name_args+=(-name "*${ext}")
+  done
+
+  local error_count=0 warning_count=0
+  local size_bytes warn_limit error_limit size_kb limit_kb
+
+  while IFS= read -r -d '' file; do
+    if [[ ${#EXEMPT_PATTERNS[@]} -gt 0 ]] && matches_list EXEMPT_PATTERNS "$file"; then
+      continue
+    fi
+
+    size_bytes=$(wc -c < "$file" | tr -d ' ')
+    warn_limit="$DEFAULT_WARN"
+    error_limit="$DEFAULT_ERROR"
+
+    if [[ -n "${EXTENDED_WARN:-}" && -n "${EXTENDED_ERROR:-}" ]] \
+       && [[ ${#EXTENDED_FILES[@]} -gt 0 ]] \
+       && matches_list EXTENDED_FILES "$file"; then
+      warn_limit="$EXTENDED_WARN"
+      error_limit="$EXTENDED_ERROR"
+    fi
+
+    if [[ "$size_bytes" -ge "$error_limit" ]]; then
+      size_kb=$(( size_bytes / 1024 )); limit_kb=$(( error_limit / 1024 ))
+      emit error "$file" "${size_kb}KB exceeds ${limit_kb}KB error limit"
+      error_count=$(( error_count + 1 ))
+    elif [[ "$size_bytes" -ge "$warn_limit" ]]; then
+      size_kb=$(( size_bytes / 1024 )); limit_kb=$(( warn_limit / 1024 ))
+      emit warning "$file" "${size_kb}KB exceeds ${limit_kb}KB warning limit"
+      warning_count=$(( warning_count + 1 ))
+    fi
+  done < <(find . -type f \( "${name_args[@]}" \) \
+    -not -path "./.git/*" -not -path "./result/*" -not -path "./node_modules/*" \
+    -print0 2>/dev/null | sort -z)
+
+  if [[ $error_count -gt 0 || $warning_count -gt 0 ]]; then
+    echo ""
+    echo "File size check: ${error_count} error(s), ${warning_count} warning(s)"
+  else
+    echo "File size check: all files within limits"
+  fi
+
+  [[ $error_count -gt 125 ]] && exit 125
+  exit "$error_count"
+}
+
+main "$@"