diff --git a/.github/workflows/checksum_addresses.yaml b/.github/workflows/checksum_addresses.yaml
new file mode 100644
index 00000000..6673b482
--- /dev/null
+++ b/.github/workflows/checksum_addresses.yaml
@@ -0,0 +1,48 @@
+name: Checksum Addresses
+
+on:
+  pull_request_target:
+    paths:
+      - 'config/*.json'
+      - 'extras/*.json'
+
+jobs:
+  checksum-addresses:
+    runs-on: ubuntu-latest
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout base (trusted script)
+        uses: actions/checkout@v4
+        with:
+          ref: ${{ github.base_ref }}
+
+      - name: Overlay PR JSON files
+        env:
+          PR_SHA: ${{ github.event.pull_request.head.sha }}
+        run: |
+          git fetch origin "$PR_SHA"
+          git checkout "$PR_SHA" -- config/ extras/ 2>/dev/null || true
+
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+
+      - name: Install dependencies
+        run: pip install eth-utils
+
+      - name: Fix address checksums
+        run: python scripts/validate_checksums.py --fix
+
+      - name: Push fixes to PR branch
+        env:
+          HEAD_REF: ${{ github.head_ref }}
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add config/*.json extras/*.json
+          if ! git diff --staged --quiet; then
+            git commit -m "chore: checksum addresses"
+            git push origin "HEAD:$HEAD_REF"
+          fi
diff --git a/scripts/validate_checksums.py b/scripts/validate_checksums.py
new file mode 100644
index 00000000..19ca6d33
--- /dev/null
+++ b/scripts/validate_checksums.py
@@ -0,0 +1,215 @@
+#!/usr/bin/env python3
+"""
+Validate that all Ethereum addresses in JSON files are checksummed (EIP-55).
+Exits with code 1 if any address is not checksummed or invalid.
+
+Usage:
+    python validate_checksums.py              # Validate extras/*.json
+    python validate_checksums.py --fix        # Fix addresses in-place
+    python validate_checksums.py file.json    # Validate specific file(s)
+"""
+
+import argparse
+import json
+import re
+import sys
+from pathlib import Path
+
+from eth_utils import is_checksum_address, to_checksum_address, is_hex_address
+
+ETH_ADDRESS_PATTERN = re.compile(r"^0x[a-fA-F0-9]{40}$")
+
+
+def _checksum_str(s):
+    """Checksum a string if it's an Ethereum address, otherwise return as-is."""
+    if ETH_ADDRESS_PATTERN.match(s) and is_hex_address(s):
+        return to_checksum_address(s)
+    return s
+
+
+def checksum_addresses_in_obj(obj):
+    """Recursively checksum all Ethereum addresses in a JSON object (keys and values)."""
+    if isinstance(obj, dict):
+        return {_checksum_str(k): checksum_addresses_in_obj(v) for k, v in obj.items()}
+    elif isinstance(obj, list):
+        return [checksum_addresses_in_obj(item) for item in obj]
+    elif isinstance(obj, str):
+        return _checksum_str(obj)
+    else:
+        return obj
+
+
+def find_addresses_in_obj(obj, path=""):
+    """Recursively find all Ethereum addresses in a JSON object (keys and values)."""
+    addresses = []
+
+    if isinstance(obj, dict):
+        for key, value in obj.items():
+            new_path = f"{path}.{key}" if path else key
+            if ETH_ADDRESS_PATTERN.match(key):
+                addresses.append((f"{path}[key]" if path else "[key]", key))
+            addresses.extend(find_addresses_in_obj(value, new_path))
+    elif isinstance(obj, list):
+        for i, item in enumerate(obj):
+            addresses.extend(find_addresses_in_obj(item, f"{path}[{i}]"))
+    elif isinstance(obj, str):
+        if ETH_ADDRESS_PATTERN.match(obj):
+            addresses.append((path, obj))
+
+    return addresses
+
+
+def validate_json_file(filepath: Path) -> list[tuple[str, str, str]]:
+    """
+    Validate all addresses in a JSON file.
+    Returns list of (path, address, issue) tuples for invalid/non-checksummed addresses.
+    """
+    issues = []
+
+    try:
+        with open(filepath) as f:
+            data = json.load(f)
+    except json.JSONDecodeError as e:
+        return [("", "", f"Invalid JSON: {e}")]
+
+    addresses = find_addresses_in_obj(data)
+
+    for json_path, address in addresses:
+        # Skip zero address
+        if address == "0x0000000000000000000000000000000000000000":
+            continue
+
+        if not is_hex_address(address):
+            issues.append((json_path, address, "Invalid hex address"))
+            continue
+
+        if not is_checksum_address(address):
+            try:
+                checksummed = to_checksum_address(address)
+                issues.append((json_path, address, f"Should be: {checksummed}"))
+            except Exception as e:
+                issues.append((json_path, address, f"Cannot checksum: {e}"))
+
+    return issues
+
+
+def fix_json_file(filepath: Path) -> tuple[int, list[tuple[str, str]]]:
+    """
+    Fix all addresses in a JSON file.
+    Returns (count of fixed addresses, list of invalid addresses that couldn't be fixed).
+    """
+    with open(filepath) as f:
+        data = json.load(f)
+
+    # Find all addresses and check for invalid ones
+    addresses = find_addresses_in_obj(data)
+    invalid = []
+    non_checksummed = 0
+
+    for json_path, addr in addresses:
+        if addr == "0x0000000000000000000000000000000000000000":
+            continue
+        if not is_hex_address(addr):
+            invalid.append((json_path, addr))
+        elif not is_checksum_address(addr):
+            non_checksummed += 1
+
+    if non_checksummed == 0:
+        return 0, invalid
+
+    # Fix valid addresses (invalid ones pass through unchanged)
+    fixed_data = checksum_addresses_in_obj(data)
+
+    # Write back with consistent formatting
+    with open(filepath, "w") as f:
+        json.dump(fixed_data, f, indent=2)
+        f.write("\n")
+
+    return non_checksummed, invalid
+
+
+def main():
+    parser = argparse.ArgumentParser(
+        description="Validate or fix Ethereum address checksums in JSON files"
+    )
+    parser.add_argument(
+        "--fix",
+        action="store_true",
+        help="Fix addresses in-place instead of validating",
+    )
+    parser.add_argument(
+        "files", nargs="*", help="JSON files to process (default: extras/*.json)"
+    )
+    args = parser.parse_args()
+
+    # Collect JSON files
+    json_files = []
+    if args.files:
+        json_files = [Path(f) for f in args.files if f.endswith(".json")]
+    else:
+        for dir_name in ["config", "extras"]:
+            dir_path = Path(dir_name)
+            if dir_path.exists():
+                json_files.extend(dir_path.glob("*.json"))
+
+    if not json_files:
+        print("No JSON files to process")
+        sys.exit(0)
+
+    if args.fix:
+        # Fix mode
+        total_fixed = 0
+        all_invalid = []
+
+        for filepath in sorted(json_files):
+            fixed, invalid = fix_json_file(filepath)
+            if fixed > 0:
+                print(f"Fixed {fixed} address(es) in {filepath}")
+                total_fixed += fixed
+            if invalid:
+                all_invalid.append((filepath, invalid))
+
+        if all_invalid:
+            print("\nInvalid addresses that cannot be checksummed:")
+            for filepath, invalid in all_invalid:
+                print(f"  {filepath}:")
+                for json_path, addr in invalid:
+                    print(f"    {json_path}: {addr}")
+            sys.exit(1)
+
+        if total_fixed > 0:
+            print(f"\nTotal: {total_fixed} address(es) fixed")
+        else:
+            print("All addresses were already checksummed")
+        sys.exit(0)
+    else:
+        # Validate mode
+        all_issues = []
+
+        for filepath in sorted(json_files):
+            issues = validate_json_file(filepath)
+            if issues:
+                all_issues.append((filepath, issues))
+
+        if all_issues:
+            print("Address checksum validation failed!\n")
+            for filepath, issues in all_issues:
+                print(f"{filepath}:")
+                for json_path, address, issue in issues:
+                    print(f"   {json_path}: {address}")
+                    print(f"      -> {issue}")
+                print()
+
+            total = sum(len(issues) for _, issues in all_issues)
+            print(f"Total: {total} address(es) need fixing")
+            print("\nRun with --fix to auto-correct")
+            sys.exit(1)
+        else:
+            print(
+                f"All {len(json_files)} JSON files have properly checksummed addresses"
+            )
+            sys.exit(0)
+
+
+if __name__ == "__main__":
+    main()