Wp Block Development Agent Skill

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/viewScriptModule)
• fixing “block invalid / not saving / attributes not persisting”
• adding dynamic rendering (render.php / render_callback)
• block deprecations and migrations (deprecated versions)
• build tooling for blocks (@wordpress/scripts, @wordpress/create-block, wp-env)

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 if using modules / viewScriptModule).

Procedure

0) Triage and locate blocks

• Run triage:
• node skills/wp-project-triage/scripts/detect_wp_project.mjs
• List blocks (deterministic scan):
• node skills/wp-block-development/scripts/list_blocks.mjs
• Identify the block root (directory containing block.json) you’re changing.

If this repo is a full site (wp-content/ present), be explicit about *which* plugin/theme contains the block.

1) Create a new block (if needed)

If you are creating a new block, prefer scaffolding rather than hand-rolling structure:

• Use @wordpress/create-block to scaffold a modern block/plugin setup.
• If you need Interactivity API from day 1, use the interactive template.

Read:

• references/creating-new-blocks.md

After scaffolding:

• Re-run the block list script and confirm the new block root.
• Continue with the remaining steps (model choice, metadata, registration, serialization).

2) Ensure apiVersion 3 (WordPress 6.9+)

WordPress 6.9 enforces apiVersion: 3 in the 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: Changing from version 2 to 3 is usually as simple as updating the apiVersion field in block.json. However:

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

Read:

• references/block-json.md (apiVersion and schema details)

3) Pick the right block model

• Static block (markup saved into post content): implement save(); keep attributes serialization stable.
• Dynamic block (server-rendered): use render in block.json (or render_callback in PHP) and keep save() minimal or null.
• Interactive frontend behavior:
• Prefer viewScriptModule for modern module-based view scripts where supported.
• If you're working primarily on data-wp-* directives or stores, also use wp-interactivity-api.

4) Update block.json safely

Make changes in the block’s block.json, then confirm registration matches metadata.

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 correctly causes “attribute not saving”

5) Register the block (server-side preferred)

Prefer PHP registration using metadata, especially when:

• you need dynamic rendering
• you need translations (wp_set_script_translations)
• you need conditional asset loading

Read and apply:

• 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/supports-and-wrappers.md
• references/dynamic-rendering.md (if dynamic)

7) Inner blocks (block composition)

If your block is a “container” that nests other blocks, treat Inner Blocks as a first-class feature:

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

Read:

• references/inner-blocks.md

8) Attributes and serialization

Before changing attributes:

• confirm where the attribute value lives (comment delimiter vs HTML vs context)
• avoid the deprecated meta attribute source

Read:

• references/attributes-and-serialization.md

9) Migrations and deprecations (avoid "Invalid block")

If you change saved markup or attributes:

• Add a deprecated entry (newest → oldest).
• Provide save for old versions and an optional migrate to normalize attributes.

Read:

• references/deprecations.md

10) Tooling and verification commands

Prefer whatever the repo already uses:

• @wordpress/scripts (common) → run existing npm scripts
• wp-env (common) → use for local WP + E2E

Read:

• references/tooling-and-testing.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 that triage recommends.

Failure modes / debugging

If something fails, start here:

• references/debugging.md (common failures + fastest checks)
• references/attributes-and-serialization.md (attributes not saving)
• references/deprecations.md (invalid block after change)

Escalation

If you’re uncertain about upstream behavior/version support, consult canonical docs first:

• WordPress Developer Resources (Block Editor Handbook, Theme Handbook, Plugin Handbook)
• Gutenberg repo docs for bleeding-edge behaviors