Error: No "sanity.json" file found in plugin "@sanity/vision

This error is happening because you're mixing Sanity Studio v2 and v3 dependencies in your monorepo. The @sanity/vision plugin you have installed is the newer v3 version, but something in your setup is trying to run it with Studio v2 commands or dependencies that expect the old sanity.json configuration file.

Here's what's happening: Sanity Studio v3 completely removed sanity.json in favor of JavaScript/TypeScript configuration files (sanity.config.js or sanity.config.ts). The v3 vision plugin doesn't have a sanity.json file because it doesn't need one - but your setup is looking for it.

How to fix it:

Option 1: Use Studio v3 (recommended)

Make sure you're fully on Studio v3:

1. Check your package.json - you should have "sanity": "^3.x.x" (not separate @sanity/core, @sanity/base, etc.)
2. Delete your sanity.json file if it exists
3. Create a sanity.config.ts (or .js) file in your Studio directory:

import {defineConfig} from 'sanity'
import {structureTool} from 'sanity/structure'
import {visionTool} from '@sanity/vision'

export default defineConfig({
  name: 'default',
  title: 'My Project',
  
  projectId: 'your-project-id',
  dataset: 'production',
  
  plugins: [
    structureTool(),
    visionTool(),
  ],
  
  schema: {
    types: [/* your schema types */],
  },
})

4. Use npm run dev or sanity dev instead of sanity start

Option 2: Use Studio v2 (not recommended - it's deprecated)

If you need to stay on v2 for some reason:

1. Downgrade vision to v2: npm install @sanity/vision@^2
2. Keep your sanity.json file
3. Use sanity start

The v2 to v3 migration is straightforward for most projects. Check out the official migration guide for a complete walkthrough. In a monorepo setup, make sure all your Sanity dependencies are aligned to the same major version across packages.