v0 API preview not supported error for shadcn/ui registry blocks

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When opening a custom shadcn/ui registry block via the https://v0.dev/chat/api/open?url= API, v0 always displays “Preview Not Supported” — even though the block code is loaded into the chat correctly.

This is not limited to custom registries. I tested with official shadcn/ui blocks and the same issue occurs:

  • https://v0.dev/chat/api/open?url=https://ui.shadcn.com/r/styles/new-york-v4/sidebar-01.json
  • https://v0.dev/chat/api/open?url=https://ui.shadcn.com/r/styles/new-york-v4/login-01.json

Both resolve with “Preview Not Supported.”

Expected Behavior

The block renders a live preview in the v0 chat, similar to how v0-generated components show previews.

Current Behavior

v0 loads the block’s code but displays “Preview Not Supported” instead of a visual preview. When asked to analyze why, v0’s AI points to missing infrastructure files:

  • package.json
  • tsconfig.json
  • next.config.mjs
  • layout.tsx
  • globals.css

These are files that v0 should scaffold automatically, and official blocks don’t include them either.

https://v0.app/chat/open-in-v0-vZrQ4QBVYbY?ref=VDB14Q

Additional Context

v0 also appears to be running an older version of the shadcn/ui registry — it doesn’t recognize components added in the October 2025 update (e.g., input-group) or newer button size variants (icon-sm).

Environment

  • Registry format: registry.json with $schema: https://ui.shadcn.com/schema/registry.json
  • Tested: February 2026
5

Experiencing almost the exact same thing when using the ShadCN registry approach with the components from our design system. It just started happening recently: Preview Not Supported. Things were working a few weeks ago (before Feb 2026).

The LLM involved in the chat does not seem to be aware of what is going on in the preview window. Once you get past some initial install infra issues as mentioned by the initial reporter of this problem, it will report “No issues found” yet all you see is Preview Not Supported. Interestingly everything works if you go directly to the generated sandboxed NextJS app. The terminal logs also look fine, yet always: Preview Not Supported. So the LLM is correct. It just doesn’t know we can’t see anything in the preview window. This is confusing our designers and they are quickly losing confidence in the tool.

Here are some more details:

  • If you use the “open in new tab” button to go to the actual sandboxed app it will render the page.
  • If you send the chat link to another user, the preview works, but never for the user that initiated the chat with the Open in V0 button (using ShadCN registry)
  • If you clear cookies, the preview will work as long as you set the proper permissions because it will sign you out.
  • If you use V0 without the shadcn registry, preview will work.

There seems to be a few js errors on the V0 chat page but can’t tell if they are relevant.

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