Short answer: use Script Manager. In your BigCommerce control panel, open the storefront settings and find Script Manager, create a new script, paste the widget's script tag, set location to footer and pages to all, and save. It applies store-wide without you touching a single theme file.
Why Script Manager is the right tool here
BigCommerce built Script Manager precisely so store owners could add third-party tags without editing Stencil theme files. That distinction matters more than it sounds.
Theme edits are fragile. Update your theme, or switch to a new one during a redesign, and anything you hand-added disappears. Script Manager entries live at the store level, so they survive theme changes entirely. When you eventually redesign your storefront, your chat widget just keeps working.
It also gives you controls you would otherwise have to code yourself: which pages the script appears on, and whether it loads in the head or the footer.
The install, step by step
In your BigCommerce control panel, go to the storefront area and open Script Manager. Create a new script.
Give it a name you will recognise later. "Clerkzo chat widget" is better than "script 3", because in a year you will be looking at this list wondering what everything does.
Set the location to footer. Chat widgets belong at the end of the body so they never delay your product images and copy from rendering.
Set the pages to all pages, unless you have a specific reason not to. Store-wide is the default you want, because a visitor on a category page is as likely to have a question as one on a product page.
Choose the script type that lets you paste a script tag directly, then paste the whole tag including its opening and closing brackets. Save.
A note on the checkout page
BigCommerce treats checkout as its own protected surface. Depending on your plan and permissions, scripts targeted at checkout are restricted, and for good reason: nobody wants third-party code running where card details are entered.
This is fine. You almost certainly do not want a chat widget on checkout anyway. Once someone is entering payment details, the job is to remove distractions, not add a floating bubble. Leave checkout alone and let the widget do its work on the pages where people are still deciding.
The theme-file alternative, and when it makes sense
You can edit your Stencil theme instead, dropping the script into the base template before the closing body tag. Two situations justify it: you need very specific placement logic that Script Manager cannot express, or you are already maintaining a custom theme in a proper development workflow.
For everyone else, it is strictly worse. It requires theme file access, it breaks on theme updates, and it makes the widget invisible to whoever inherits the store after you. Use Script Manager.
Verifying it went live
Open your storefront on the live domain, not the preview link, in a private browser window. The bubble should appear in the corner shortly after the page loads.
Then check a product page, a category page and your homepage. Script Manager's page targeting means it is genuinely possible for the script to be on one and not another, especially if you narrowed the scope while experimenting.
If the bubble is missing, view page source and search for your script tag. In the source but not rendering means an error, so open the browser console. Not in the source means the Script Manager entry is not applying to that page type, or it saved as inactive.
Common gotchas
Preview versus live storefront. BigCommerce theme previews do not always execute store-level scripts. Judge from the real storefront.
Store-level caching and CDN. Your storefront is served through a CDN. A change can take a short while to propagate. Wait a couple of minutes and use a private window before concluding it failed.
AMP pages. If you serve AMP versions of any pages, custom JavaScript will not run there. AMP forbids arbitrary scripts by design. Your chat widget will be absent from AMP pages and there is no workaround, only the choice to stop serving AMP for those pages.
Duplicate scripts. If you previously tried an app that injected the same widget, you can end up with two bubbles. Check Script Manager and your installed apps before adding another entry.
Content security policy. If you have added a restrictive CSP to your storefront, you must allow the widget's domain or the browser blocks it silently. The console will tell you.
Making it useful for an actual store
An ecommerce store has a different job to a service business. Most of your chat volume will be shipping times, returns policy, sizing, stock and order status. Those are exactly the questions that eat your inbox.
Train the widget by pointing it at your store so it crawls product and policy pages, then upload a knowledge file for anything not published, like your internal returns rules or a size guide that only exists as a PDF. Set guardrails so it stays on topic and hands off to a human rather than improvising on refunds. And when a pre-sales question turns into a real opportunity, capture the details rather than letting the conversation end in the browser.
That last part is the money bit, and it is covered in how to capture more leads from your website.
Frequently asked questions
Does this need an app from the BigCommerce marketplace?
No. A script tag through Script Manager is enough. That also means nothing extra to update or uninstall later.
Will it slow down my store?
Loaded in the footer and asynchronously, it does not block your page rendering. Your product pages paint first.
Can I show it only on product pages?
Yes. Script Manager's page targeting supports narrowing scope, though store-wide is usually the better choice.
Can it answer questions about specific products?
It answers from what it has learned by crawling your site, so published product information is fair game. Live stock levels and order status are a different problem and generally belong with a human handoff.
What does it cost per conversation?
Nothing. Clerkzo is flat monthly pricing, which matters for a store where traffic spikes are normal.