WP Block Development

When to use

Use this skill for block work such as:

• creating a new block or updating an existing one
• changing block.json (scripts/styles/supports/attributes/render)
• fixing "block invalid / not saving / attributes not persisting"
• adding dynamic rendering (render.php / render_callback)
• block deprecations and migrations (deprecated versions)
• build tooling (@wordpress/scripts, @wordpress/create-block)
• block patterns and variations

Inputs required

• Repo root and target (plugin vs theme vs full site).
• The block name/namespace and where it lives (path to block.json if known).
• Target WordPress version range (especially for viewScriptModule / apiVersion 3).

Procedure

0) Triage and locate blocks

1. Search for existing block.json files
2. Search for register_block_type calls
3. Identify the block root (directory containing block.json)

1) Create a new block (if needed)

If creating a new block, prefer scaffolding:

npx @wordpress/create-block@latest my-custom-block

For interactive blocks, use the interactive template.

Read:

• references/creating-blocks.md

2) Ensure apiVersion 3 (WordPress 6.9+)

WordPress 6.9 enforces apiVersion: 3 in block.json schema. Blocks with apiVersion 2 or lower trigger console warnings when SCRIPT_DEBUG is enabled.

Why this matters:

• WordPress 7.0 will run the post editor in an iframe regardless of block apiVersion
• apiVersion 3 ensures your block works correctly inside the iframed editor (style isolation, viewport units, media queries)

Migration from apiVersion 2:

1. Update the apiVersion field in block.json to 3
2. Test in a local environment with the iframe editor enabled
3. Ensure any style handles are included in block.json (styles missing from the iframe won't apply)
4. Third-party scripts attached to a specific window may have scoping issues

{
  "apiVersion": 3,
  "name": "my-plugin/my-block",
  "...": "..."
}

Read:

• references/block-json.md

3) Pick the right block model

• Static block (markup saved into post content): implement save()
• Dynamic block (server-rendered): use render in block.json and keep save() minimal or null
• Interactive frontend: use viewScriptModule for modern module-based view scripts

viewScript vs viewScriptModule:

Property	viewScript	viewScriptModule
Module type	Classic script	ES Module
Loading	Synchronous	Async/deferred
Use for	Legacy/compatibility	Interactivity API, modern JS
Dependencies	Manual registration	Import statements

{
  "viewScript": "file:./view.js",
  "viewScriptModule": "file:./view.js"
}

Prefer viewScriptModule for:

• Interactivity API (@wordpress/interactivity)
• Modern ES module imports
• Better performance (deferred loading)

4) Update block.json safely

For field-by-field guidance:

Read:

• references/block-json.md

Common pitfalls:

• Changing name breaks compatibility (treat it as stable API)
• Changing saved markup without adding deprecated causes "Invalid block"
• Adding attributes without defining source/serialization causes "attribute not saving"

5) Register the block (server-side preferred)

Prefer PHP registration using metadata for:

• Dynamic rendering
• Translations (wp_set_script_translations)
• Conditional asset loading

Read:

• references/registration.md

6) Implement edit/save/render patterns

Follow wrapper attribute best practices:

• Editor: useBlockProps()
• Static save: useBlockProps.save()
• Dynamic render (PHP): get_block_wrapper_attributes()

Read:

• references/edit-save-render.md

7) Inner blocks (block composition)

If your block is a container that nests other blocks:

• Use useInnerBlocksProps() to integrate inner blocks with wrapper props
• Keep migrations in mind if you change inner markup

Read:

• references/inner-blocks.md

8) Block patterns and variations

• Patterns: predefined block arrangements
• Variations: different configurations of a single block

Read:

• references/patterns-variations.md

9) Migrations and deprecations

If you change saved markup or attributes:

1. Add a deprecated entry (newest → oldest)
2. Provide save for old versions and optional migrate

Read:

• references/deprecations.md

Verification

• Block appears in inserter and inserts successfully.
• Saving + reloading does not create "Invalid block".
• Frontend output matches expectations (static: saved markup; dynamic: server output).
• Assets load where expected (editor vs frontend).
• Run the repo's lint/build/tests.

Failure modes / debugging

• "Invalid block content" after changes:
  • Missing deprecation entry, changed markup without migration
• Block attributes not saving:
  • Missing source definition, wrong attribute type, serialization mismatch
• Block not appearing in inserter:
  • Registration failed, wrong category, PHP fatal error
• Styles not applying in editor:
  • Missing editorStyle in block.json, wrong asset path

Read:

• references/debugging.md

Escalation

For canonical detail, consult:

• Block Editor Handbook
• Block API Reference
• Gutenberg Storybook