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Use this path when you need a block with custom rendering logic, references to Sanity documents (sponsors, projects, events), or Portable Text content. For connecting an existing fulldev/ui template to Sanity without writing a new component, see Wiring a template block.
Before you start, make sure you are on a feature branch created from preview: git checkout preview && git pull && git checkout -b feat/block-your-block-name.

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Overview

Adding a custom block touches five areas:
  1. Sanity schema — define the block’s fields
  2. Schema registration — add the block to the studio
  3. fulldev/ui primitives — install any UI components the block needs
  4. Astro component — implement the block using the flat-props pattern
  5. GROQ projection and typegen — expose the data and generate types

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Steps

1

Create the Sanity schema

Create a new file in studio/src/schemaTypes/blocks/. Use the defineBlock helper, which automatically adds the shared base fields (backgroundVariant, spacing, maxWidth) to every block and generates a collapsible Layout Options fieldset.
// studio/src/schemaTypes/blocks/your-block.ts
import { defineField, defineArrayMember } from 'sanity'
import { defineBlock } from '../helpers/defineBlock'

export const yourBlock = defineBlock({
  name: 'yourBlock',          // camelCase — must match PascalCase filename with lowercased first char
  title: 'Your Block',        // displayed in Sanity Studio
  fields: [
    defineField({
      name: 'heading',
      title: 'Heading',
      type: 'string',
      validation: (Rule) => Rule.required(),
    }),
    defineField({
      name: 'description',
      title: 'Description',
      type: 'text',
    }),
    defineField({
      name: 'items',
      title: 'Items',
      type: 'array',
      of: [defineArrayMember({ type: 'yourItemObject' })],
    }),
  ],
})
The defineBlock helper also supports variants (for layout variant radio buttons), hiddenByVariant (to hide fields based on the selected variant), and an icon for the Sanity Studio block picker.For reference, here is how heroBanner uses variants and hiddenByVariant:
// studio/src/schemaTypes/blocks/hero-banner.ts
import { defineField, defineArrayMember } from 'sanity'
import { RocketIcon } from '@sanity/icons'
import { defineBlock } from '../helpers/defineBlock'

export const heroBanner = defineBlock({
  name: 'heroBanner',
  title: 'Hero Banner',
  icon: RocketIcon,
  variants: [
    { name: 'centered', title: 'Centered' },
    { name: 'split', title: 'Split' },
    { name: 'overlay', title: 'Overlay' },
    { name: 'spread', title: 'Spread' },
  ],
  hiddenByVariant: {
    alignment: ['split', 'spread'],  // hide 'alignment' when variant is split or spread
  },
  fields: [
    defineField({ name: 'heading', title: 'Heading', type: 'string',
      validation: (Rule) => Rule.required() }),
    defineField({ name: 'subheading', title: 'Subheading', type: 'string' }),
    defineField({
      name: 'ctaButtons',
      title: 'CTA Buttons',
      type: 'array',
      of: [defineArrayMember({ type: 'button' })],
    }),
    defineField({
      name: 'alignment',
      title: 'Alignment',
      type: 'string',
      fieldset: 'layout',
      options: { list: ['left', 'center', 'right'], layout: 'radio' },
      initialValue: 'center',
    }),
  ],
})
2

Register the schema

Open studio/src/schemaTypes/index.ts and add two things:1. Import the schema at the top:
import { yourBlock } from './blocks/your-block'
2. Add it to the schemaTypes array:
export const schemaTypes: SchemaTypeDefinition[] = [
  // ... existing schemas ...
  yourBlock,   // add here, grouped with other block schemas
]
Then open the page schema at studio/src/schemaTypes/documents/page.ts and add yourBlock to the blocks[] array’s of list so editors can select it:
defineField({
  name: 'blocks',
  title: 'Blocks',
  type: 'array',
  of: [
    // ... existing block types ...
    defineArrayMember({ type: 'yourBlock' }),
  ],
})
3

Install fulldev/ui primitives

If your block needs UI components (buttons, badges, icons, images), install them from the fulldev registry via the shadcn CLI. Do not copy components manually.
# From the astro-app directory
npx shadcn@latest add @fulldev/button
npx shadcn@latest add @fulldev/badge
npx shadcn@latest add @fulldev/section
Installed components land in astro-app/src/components/ui/. Import them from @/components/ui/{name}.Skip this step if your block only uses components that are already installed.
4

Create the Astro component

Create astro-app/src/components/blocks/custom/YourBlock.astro. The filename must be PascalCase and the first character lowercased must match the schema name exactly (YourBlock → yourBlock).All blocks use the flat-props pattern: interface Props extends YourBlockBlock and destructure fields directly from Astro.props.
---
// astro-app/src/components/blocks/custom/YourBlock.astro
import type { YourBlockBlock } from '@/lib/types';
import { Section, SectionContent, SectionActions } from '@/components/ui/section';
import { Button } from '@/components/ui/button';
import { stegaClean } from '@sanity/client/stega';

interface Props extends YourBlockBlock {
  class?: string;
  id?: string;
}

// Destructure fields directly — not from a nested object
const { heading, description, items, class: className, id } = Astro.props;
---

<Section class={className} id={id} data-animate>
  <SectionContent>
    <h2>{heading}</h2>
    {description && <p>{description}</p>}
    <!-- Compose from ui/ primitives + Tailwind utilities -->
  </SectionContent>
</Section>
Key conventions:
  • Use stegaClean(value) on any string field used for logic (variant selection, conditional rendering). Raw strings from Sanity may contain stega metadata in the preview branch.
  • Compose from components in src/components/ui/ — do not write raw HTML for things buttons or badges cover.
  • Add data-animate to the outer <Section> to opt into the intersection-observer entrance animation.
  • Interactivity goes in a <script> tag using vanilla JS with data-attribute event delegation. Keep each handler under 50 lines.
Because block-registry.ts uses import.meta.glob, the file is automatically registered as soon as it exists. No other file needs to be updated.
5

Add the GROQ projection and run typegen

Open astro-app/src/lib/sanity.ts (or the relevant query file) and add a projection for your block type inside the blocks[] projection. The projection reshapes Sanity’s data into the flat structure your component expects.
// Example projection fragment inside the page blocks[] array projection
_type == 'yourBlock' => {
  _type,
  _key,
  heading,
  description,
  backgroundVariant,
  spacing,
  maxWidth,
  items[] {
    // project each item's fields
  },
},
After adding the projection, regenerate TypeScript types:
npm run typegen
This creates the YourBlockBlock type that your component imports from @/lib/types.Finally, build and verify Lighthouse scores hold at 90+:
npm run build --workspace=astro-app

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Checklist

Before opening a PR, confirm:
  • Schema file created in studio/src/schemaTypes/blocks/
  • Schema imported and added to schemaTypes array in index.ts
  • Block type added to the page schema’s blocks[] array
  • Astro component created in blocks/custom/ with PascalCase filename
  • Component uses interface Props extends YourBlockBlock (flat-props pattern)
  • stegaClean used on any string used for conditional logic
  • GROQ projection added and npm run typegen run successfully
  • Block renders correctly in local dev with npm run dev
  • Lighthouse scores remain at 95+ Performance, 90+ Accessibility
Write a Storybook story (YourBlock.stories.ts) alongside the component so the block is visible in the component library without needing real Sanity data. See existing stories in blocks/custom/ for the pattern.