diff --git a/.github/scripts/update-tool-checksums.sh b/.github/scripts/update-tool-checksums.sh
new file mode 100755
index 0000000..9b4f15e
--- /dev/null
+++ b/.github/scripts/update-tool-checksums.sh
@@ -0,0 +1,158 @@
+#!/usr/bin/env bash
+#
+# Recalculate and optionally apply the SHA-256 checksums of the pinned CI tools.
+#
+# Renovate bumps the version numbers but cannot compute a checksum, so without
+# this the pinned hash keeps pointing at the previous release and every bump
+# fails the build with "computed checksum did NOT match". The workflow in
+# .github/workflows/update-checksums.yml runs this on Renovate's own pull
+# requests and commits the result back onto the branch.
+#
+# The hash is not simply taken from whatever the download happened to return.
+# Each project publishes its own checksum file next to the release; the
+# download is verified against that first, and only a verified hash is written
+# into the repository.
+#
+# Usage:
+#   .github/scripts/update-tool-checksums.sh           # show, then ask
+#   .github/scripts/update-tool-checksums.sh --apply    # write without asking
+#
+
+set -euo pipefail
+
+readonly RED='\033[0;31m' GREEN='\033[0;32m' YELLOW='\033[1;33m' BLUE='\033[0;34m' NC='\033[0m'
+
+Write-Log() {
+    local level=$1; shift
+    local color=$NC
+    case $level in
+        INFO)    color=$BLUE ;;
+        SUCCESS) color=$GREEN ;;
+        WARN)    color=$YELLOW ;;
+        ERROR)   color=$RED ;;
+    esac
+    if [[ $level == ERROR ]]; then
+        echo -e "${color}[$level]${NC} $*" >&2
+    else
+        echo -e "${color}[$level]${NC} $*"
+    fi
+}
+
+Stop-Script() {
+    Write-Log ERROR "$1"
+    exit 1
+}
+
+Show-Usage() {
+    cat <<'EOF'
+Usage: update-tool-checksums.sh [--apply]
+
+Options:
+  --apply     Write the checksums without prompting
+  -h, --help  Show this help
+EOF
+}
+
+APPLY=false
+while [[ $# -gt 0 ]]; do
+    case "$1" in
+        --apply) APPLY=true; shift ;;
+        -h|--help) Show-Usage; exit 0 ;;
+        *) Write-Log ERROR "Unknown argument: $1"; Show-Usage; exit 1 ;;
+    esac
+done
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/../.." && pwd)"
+readonly REPO_ROOT
+cd "$REPO_ROOT"
+
+readonly CONFIG_VALIDATION=".github/workflows/config-validation.yml"
+readonly PR_CHECKS=".github/workflows/pr-checks.yml"
+
+# ── Reading and writing the pinned values ───────────────────────────────────
+
+# Usage: Get-KeyValue <file> <KEY>   ->  value of `KEY: "value"`
+Get-KeyValue() {
+    sed -n "s/^[[:space:]]*$2:[[:space:]]*\"\([^\"]*\)\".*/\1/p" "$1" | head -n1
+}
+
+# Usage: Set-KeyValue <file> <KEY> <value>
+Set-KeyValue() {
+    sed -i "s|^\([[:space:]]*$2:[[:space:]]*\"\)[^\"]*\"|\1$3\"|" "$1"
+}
+
+# ── Fetching and verifying ──────────────────────────────────────────────────
+
+TEMP_DIR="$(mktemp -d)"
+trap 'rm -rf -- "$TEMP_DIR"' EXIT
+
+# Usage: Get-VerifiedHash <name> <artifact-url> <expected-sha256>
+# Downloads the artifact, checks it against the hash the project published, and
+# echoes that hash. Refuses to return anything if the two disagree.
+Get-VerifiedHash() {
+    local name=$1 url=$2 expected=$3
+    local file="$TEMP_DIR/$name"
+
+    [[ "$expected" =~ ^[a-f0-9]{64}$ ]] || Stop-Script "$name: no valid checksum published upstream (got: '$expected')"
+
+    curl -sSL --fail-with-body --retry 5 --retry-delay 3 --retry-all-errors -o "$file" "$url" \
+        || Stop-Script "$name: download failed ($url)"
+
+    local actual
+    actual="$(sha256sum "$file" | awk '{print $1}')"
+
+    if [[ "$actual" != "$expected" ]]; then
+        Stop-Script "$name: download does not match the published checksum. published=$expected downloaded=$actual"
+    fi
+
+    echo "$actual"
+}
+
+# Usage: Get-PublishedHash <url> <grep-pattern>
+# Pulls one line out of a checksums file and returns the hash on it.
+Get-PublishedHash() {
+    curl -sSL --fail-with-body --retry 5 --retry-delay 3 --retry-all-errors "$1" \
+        | grep -- "$2" | awk '{print $1}' | head -n1
+}
+
+# ── The tools ───────────────────────────────────────────────────────────────
+
+ACTIONLINT_VERSION="$(Get-KeyValue "$CONFIG_VALIDATION" ACTIONLINT_VERSION)"
+LYCHEE_VERSION="$(Get-KeyValue "$PR_CHECKS" LYCHEE_VERSION)"
+
+for pair in "actionlint:$ACTIONLINT_VERSION" "lychee:$LYCHEE_VERSION"; do
+    [[ -n "${pair#*:}" ]] || Stop-Script "Could not read the ${pair%%:*} version. Did the file layout change?"
+done
+
+Write-Log INFO "Versions found in the repository:"
+echo "  actionlint:  $ACTIONLINT_VERSION"
+echo "  lychee:      $LYCHEE_VERSION"
+echo
+
+Write-Log INFO "Downloading and verifying against the published checksums..."
+
+ACTIONLINT_SHA256="$(Get-VerifiedHash "actionlint.tar.gz" \
+    "https://github.com/rhysd/actionlint/releases/download/v${ACTIONLINT_VERSION}/actionlint_${ACTIONLINT_VERSION}_linux_amd64.tar.gz" \
+    "$(Get-PublishedHash "https://github.com/rhysd/actionlint/releases/download/v${ACTIONLINT_VERSION}/actionlint_${ACTIONLINT_VERSION}_checksums.txt" "linux_amd64.tar.gz")")"
+Write-Log SUCCESS "actionlint: $ACTIONLINT_SHA256"
+
+LYCHEE_SHA256="$(Get-VerifiedHash "lychee.tar.gz" \
+    "https://github.com/lycheeverse/lychee/releases/download/lychee-v${LYCHEE_VERSION}/lychee-x86_64-unknown-linux-gnu.tar.gz" \
+    "$(Get-PublishedHash "https://github.com/lycheeverse/lychee/releases/download/lychee-v${LYCHEE_VERSION}/lychee-x86_64-unknown-linux-gnu.tar.gz.sha256" "")")"
+Write-Log SUCCESS "lychee:     $LYCHEE_SHA256"
+
+echo
+if [[ "$APPLY" != true ]]; then
+    read -rp "Write these checksums into the repository? [y/N] " response
+    if [[ ! "$response" =~ ^[Yy]$ ]]; then
+        Write-Log INFO "No changes made"
+        exit 0
+    fi
+fi
+
+Set-KeyValue "$CONFIG_VALIDATION" ACTIONLINT_SHA256 "$ACTIONLINT_SHA256"
+Set-KeyValue "$PR_CHECKS" LYCHEE_SHA256 "$LYCHEE_SHA256"
+
+Write-Log SUCCESS "Updated:"
+echo "  - $CONFIG_VALIDATION"
+echo "  - $PR_CHECKS"
diff --git a/.github/workflows/update-checksums.yml b/.github/workflows/update-checksums.yml
new file mode 100644
index 0000000..32dfa43
--- /dev/null
+++ b/.github/workflows/update-checksums.yml
@@ -0,0 +1,56 @@
+# Copyright (C) 2026 Sten Tijhuis
+# SPDX-License-Identifier: MIT
+name: Update tool SHA256 checksums
+
+# Renovate bumps the pinned tool versions but cannot compute a checksum, so on
+# its own every bump lands with the previous release's hash still in place and
+# the build stops at "computed checksum did NOT match". This recalculates the
+# hashes on Renovate's pull requests and commits them back onto the branch.
+#
+# Renovate must be told to ignore those commits, or it treats the branch as
+# modified by someone else and stops maintaining the pull request. That is the
+# gitIgnoredAuthors entry in renovate.json.
+
+on:
+  pull_request:
+    types: [opened, synchronize, reopened]
+    branches: [main, development]
+    paths:
+      - '.github/workflows/config-validation.yml'
+      - '.github/workflows/pr-checks.yml'
+      - '.github/scripts/update-tool-checksums.sh'
+
+permissions: {}
+
+jobs:
+  update-checksums:
+    name: Recalculate SHA256 checksums
+    runs-on: ubuntu-latest
+    # Only Renovate's own branches. Running this on a human's pull request
+    # would mean pushing commits to a branch someone is actively working on.
+    if: startsWith(github.head_ref, 'renovate/') && github.actor == 'renovate[bot]'
+    permissions:
+      contents: write
+    steps:
+      - name: Check out the pull request branch
+        uses: actions/checkout@3d3c42e5aac5ba805825da76410c181273ba90b1 # v7.0.1
+        with:
+          ref: ${{ github.head_ref }}
+
+      # The script verifies each download against the checksum the project
+      # publishes next to the release before writing anything, so a hash only
+      # lands here if upstream vouches for it too.
+      - name: Recalculate and apply checksums
+        run: .github/scripts/update-tool-checksums.sh --apply
+
+      - name: Commit updated checksums
+        run: |
+          git config user.name "github-actions[bot]"
+          git config user.email "github-actions[bot]@users.noreply.github.com"
+          git add .github/workflows/config-validation.yml .github/workflows/pr-checks.yml
+          if git diff --staged --quiet; then
+            echo "Checksums are already up to date, nothing to commit."
+          else
+            git commit -m "chore: update tool SHA256 checksums"
+            git push
+          fi
diff --git a/renovate.json b/renovate.json
index 94c4088..d8e6177 100644
--- a/renovate.json
+++ b/renovate.json
@@ -6,6 +6,10 @@
   "timezone": "Europe/Amsterdam",
   "forkProcessing": "enabled",
   "pinDigests": true,
+  "gitIgnoredAuthors": [
+    "github-actions[bot]@users.noreply.github.com",
+    "41898282+github-actions[bot]@users.noreply.github.com"
+  ],
   "assigneesFromCodeOwners": true,
   "reviewersFromCodeOwners": true,
   "enabledManagers": [