/sanity-best-practices

Sanity Image Rules

1. Schema Definition

Always enable hotspot: true. This allows editors to control cropping and the focal point.

defineField({
  name: 'mainImage',
  title: 'Main Image',
  type: 'image',
  options: {
    hotspot: true // CRITICAL
  },
  fields: [
    defineField({
      name: 'alt',
      type: 'string',
      title: 'Alternative Text',
      validation: rule => rule.required().warning('Alt text is important for SEO')
    })
  ]
})

2. URL Builder (urlFor)

Use the Sanity Image URL Builder to generate optimized URLs (resize, crop, format).

Setup (sanity/lib/image.ts):

import createImageUrlBuilder from '@sanity/image-url'
import { dataset, projectId } from '../env'

const builder = createImageUrlBuilder({ projectId, dataset })

export const urlFor = (source: any) => {
  return builder.image(source)
}

Usage: The URL builder automatically uses hotspot/crop data when available:

const imageUrl = urlFor(mainImage)
  .width(800)
  .height(600)
  .fit('crop')  // Respects hotspot when cropping
  .url()

3. Next.js Image Component Pattern

Create a reusable SanityImage component that handles the urlFor logic and next/image props.

import Image from 'next/image'
import { urlFor } from '@/sanity/lib/image'

interface SanityImageProps {
  value: any // SanityImageSource
  width?: number
  height?: number
  className?: string
  priority?: boolean
}

export function SanityImage({ value, width = 800, height, className, priority }: SanityImageProps) {
  if (!value?.asset) return null

  return (
    <Image
      className={className}
      src={urlFor(value)
        .width(width)
        .height(height || Math.round(width / 1.5)) // Default aspect ratio if no height
        .url()}
      alt={value.alt || ''}
      width={width}
      height={height || Math.round(width / 1.5)}
      priority={priority}
      // Optional: Use LQIP (Low Quality Image Placeholder)
      placeholder={value.asset.metadata?.lqip ? 'blur' : 'empty'}
      blurDataURL={value.asset.metadata?.lqip}
    />
  )
}

4. Querying Images

Critical: LQIP (Low Quality Image Placeholder) is not automatic. You must explicitly query it via asset->{ metadata { lqip } }.

Minimal Query (No LQIP)

mainImage {
  asset->{ _id, url },
  alt
}

Full Query (With LQIP & Dimensions)

mainImage {
  asset->{
    _id,
    url,
    metadata {
      lqip,                          // Base64 blur placeholder
      dimensions { width, height }   // For aspect ratio
    }
  },
  alt,
  hotspot,  // Include if using hotspot cropping
  crop      // Include if using cropping
}

Why this matters: Without querying metadata.lqip, the blurDataURL in your component will be undefined and the blur effect won't work.

5. Performance Tips

• Auto Format: Sanity CDN automatically serves WebP/AVIF if the browser supports it (no need to specify .format('webp') manually in most cases, but next/image handles this too).
• Sizing: Always request the exact size you need using .width() and .height() in urlFor. Don't download a 4000px image for a thumbnail.