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Written by: Ronnel DG Last updated: 21 Aug., 2026 |
Backend file storage lets users of your site upload their own files and images, such as a member's profile photo or a document a client attaches to a form. It's part of Backends, the feature that adds app-like capabilities to your B12 site, and the AI Agent builds and configures it for you. This is different from uploading your own files to show on your site, so this article explains when you need each one and how to request it.
Backend file storage vs. uploading website files
B12 has two kinds of file storage, and it's easy to mix them up. The difference comes down to who does the uploading and when.
| Uploading website files | Backend file storage | |
|---|---|---|
| Who uploads | You, the site owner | You or your visitors or users/members |
| When | While you build or edit your site | Anytime, while people use your live site |
| Examples | Your logo, static photos, PDFs you link to | User profile photos, uploaded resumes, members' personal files |
| Where files live | B12's CDN (Content Delivery Network) | A secure storage bucket with its own privacy setting |
| How to set it up | Upload files through your B12 Editor | Ask the AI Agent to build the specific storage functionality you need |
Note: If you only want to add your own files to your site, you don't need backend file storage. See Uploading website files and resources instead.
When to use backend file storage
You need backend file storage whenever someone other than you uploads a file while using your site or if you need to display files or images dynamically based on criteria like user access. Common examples include:
- Profile photos and avatars for members on an account page
- Product images a seller adds to a community board, portfolio, or listing
- Documents such as resumes, contracts, or completed application forms that clients upload
- Photos or images submitted through a form, intake flow, or member portal
You don't have to set anything up in advance. Whenever you ask for a feature that involves an upload, the AI Agent adds the storage and the upload controls at the same time.
What a storage bucket is
B12's backend file storage is powered by Supabase, a secure service for storing files and data. Supabase keeps uploaded files in a storage bucket: a labeled container for files, a bit like a folder, that has its own privacy setting.
Each bucket is either public, meaning anyone can view the files, or private, meaning only the people you allow can view them. The AI Agent creates the buckets and sets the right privacy level as it builds your feature, so there's nothing for you to install or manage.
Asking the AI Agent to add uploads
To add an upload, describe the feature in plain language: where the upload should appear, who it's for, and who should be able to see the files. The AI Agent builds the upload field, connects it to storage, and sets the privacy level for you. Here are a few examples you can copy and adjust:
Add a profile photo upload to my [member profile] page so signed-in members can add and change their picture.
Let customers upload product images when they add a listing on my [Sell] page.
Add a document upload to my [intake] form so clients can attach [PDFs and contracts], and keep these files private.
The first time you ask for a feature that needs storage, the AI Agent may show a card in the chat to turn on Backends. Select Enable, and the AI Agent continues building your feature.
Tip: Tell the AI Agent who should be able to see the uploaded files. Saying "only signed-in clients can view these documents" helps it set the right privacy level from the start.
Frequently asked questions
→ Do I need to turn on backend file storage before I can use it?
⇒ No. When you ask for a feature that involves uploads, the AI Agent turns on Backends and sets up the storage automatically. There's no separate step to enable first.
→ Can visitors see files that are meant to be private?
⇒ No. The AI Agent marks sensitive files, such as documents, as private by default. Private files are viewable only by the people you allow, such as signed-in members.
→ Can I change a file from public to private later?
⇒ Yes. Ask the AI Agent to change the access level for that feature, and it will update the setting for you.
→ What kinds of files can people upload, and how large can they be?
⇒ Any file type is supported, and each file can be up to 50 MB. If a specific file type or size doesn't work, ask the AI Agent what's allowed.