Blogger automatically injects CSS and JavaScript files that can slow down your site. If you build or maintain your own theme, you can safely disable those assets to improve performance — with a few caveats. This guide shows how, plus a safe alternative for cookie notices and contact forms.
Why these default files matter
Blogger inserts several default resources into every page. Two of the most common are:
- widget_css_bundle.css — a reset/utility stylesheet and widget styles.
- widget.js — JavaScript that powers many built-in widgets and some template features.
If you use a custom theme that provides its own, well-optimized styles and widget logic, these injected files can be redundant and may delay above-the-fold rendering and increase page weight.
Quick method: disable the injected CSS and JS (recommended for custom themes)
To stop Blogger from injecting those default files at the template level, add these attributes to the top-level <html> tag in your theme HTML (Template > Edit HTML):
<html b:css='false' b:js='false'>What this does: prevents automatic insertion of widget_css_bundle.css and widget.js.
Important caveats
- The built-in contact form widget will stop working.
- The Blogger dashboard Design → Layout widget editor may not behave as expected (you may lose drag-and-drop editing for some widgets).
- If you later need those features, revert the attributes or selectively add back parts you need.
Alternative: block widget.js execution (keeps Design tab usable)
If you want to keep Blogger’s Design interface available but prevent the script from executing on the live site, use this approach. It blocks execution while preserving the template code that Dashboard features expect.
- Open your template HTML and find the closing
</body>tag. - Replace it with this (paste exactly):
<textarea hidden id='bjs'></body></textarea>
</body>Then add this CSS (anywhere in your theme CSS) to ensure the textarea never appears:
[hidden] { display: none !important; }Finally, add the following JavaScript before the closing </body> to re-enable the cookie notice (if present) and to safely load that script only when needed:
<script>
const REG_EXP = /cookieOptions\.(\w+)\) \|\| '(.+)'/g;
const cookieJs = '/js/cookienotice.js';
const textarea = document.getElementById('bjs');
const loadScript = (src) => new Promise((resolve, reject) => {
const s = document.createElement('script');
s.src = src;
s.onload = resolve;
s.onerror = reject;
document.body.appendChild(s);
});
const decodeHtml = (string) => string.replace(/\\x(\w{2})/g, (_, hex) => String.fromCharCode(parseInt(hex, 16)));
const loadCookieScript = () => {
if (!textarea) return;
const content = textarea.value || '';
const cookieOptions = window.cookieOptions || {};
const Default = {};
content.replace(REG_EXP, (_, key, value) => {
Default[key] = decodeHtml(value);
});
if (content.includes(cookieJs)) {
loadScript(new URL(cookieJs, window.location.origin).href)
.then(() => {
const { msg = Default.msg, close = Default.close, learn = Default.learn, link = Default.link } = cookieOptions;
if (typeof window.cookieChoices?.showCookieConsentBar === 'function') {
cookieChoices.showCookieConsentBar(msg, close, learn, link);
}
})
.catch(console.error);
}
};
if (textarea) {
loadCookieScript();
textarea.remove();
}
</script>This approach stops widget.js from executing on page load while keeping template code in place for the Dashboard. The contact form still won’t work; consider using a light external form (see below).
Replace the contact form with a lightweight external service
If you lose the built-in contact widget, use a simple external alternative that works with plain HTML:
- Formspree — simple to set up and privacy-friendly.
- Netlify Forms — if you host form endpoint elsewhere.
- Or build a small serverless endpoint to accept form submissions.
Example Formspree markup:
<form action="https://formspree.io/f/YOUR_ID" method="POST">
<label>Name<input name="name"></label>
<label>Email<input type="email" name="_replyto"></label>
<label>Message<textarea name="message"></textarea></label>
<button type="submit">Send</button>
</form>Best practices & checklist
- Always backup your template before editing (Template → Backup).
- Test on a staging copy of your blog, if possible.
- Measure performance before and after with PageSpeed Insights or another audit tool.
- Defer or lazy-load non-critical JS and inline critical CSS for faster First Contentful Paint (FCP).
FAQ
Q: Is it safe to remove those files?
A: Yes, if your theme doesn't rely on them. For custom themes that include their own styles and JS, removing the injected files often improves performance. If you use a third-party theme that expects those files, do not remove them.
Q: Will removing them affect AdSense approval?
A: No—removing widget_css_bundle.css or blocking execution of widget.js doesn’t conflict with AdSense rules by itself. What matters for AdSense approval is content policy compliance and correct ad script placement. Do not remove or block Google ad scripts.
Q: I need the contact form. What should I do?
A: Replace it with Formspree or any lightweight external form handler. That gives you a working contact form without the extra Blogger JS overhead.
Q: Can I revert the changes?
A: Yes. Remove b:css='false' and/or b:js='false' from your <html> tag, or undo the textarea replacement to restore original behavior.
Q: Will this improve SEO?
A: Indirectly. Faster page load and improved Core Web Vitals help search ranking. But content relevance and quality remain the most important ranking factors.
Thanks for reading! If you want, I can generate a ready-to-paste version of your theme header/footer with these changes, or prepare a rollback script to make testing safer.