Agent Skills: WP Plugin Development

WP Plugin Development

When to use

Use this skill for plugin work such as:

• creating or refactoring plugin structure (bootstrap, includes, namespaces/classes)
• adding hooks/actions/filters
• activation/deactivation/uninstall behavior and migrations
• adding settings pages / options / admin UI (Settings API)
• security fixes (nonces, capabilities, sanitization/escaping, SQL safety)
• packaging a release (build artifacts, readme, assets)

Inputs required

• Repo root + target plugin(s) (path to plugin main file if known).
• Where this plugin runs: single site vs multisite; WP.com conventions if applicable.
• Target WordPress + PHP versions (affects available APIs).

Procedure

0) Triage and locate plugin entrypoints

1. Identify the main plugin file (contains Plugin Name: header)
2. Check for existing structure (includes/, admin/, public/ directories)
3. Note any existing hooks or class patterns

1) Follow a predictable architecture

Guidelines:

• Keep a single bootstrap (main plugin file with header).
• Avoid heavy side effects at file load time; load on hooks.
• Prefer a dedicated loader/class to register hooks.
• Keep admin-only code behind is_admin() (or admin hooks) to reduce frontend overhead.

Read:

• references/structure.md

2) Hooks and lifecycle (activation/deactivation/uninstall)

Activation hooks are fragile; follow guardrails:

• Register activation/deactivation hooks at top-level, not inside other hooks
• Flush rewrite rules only when needed and only after registering CPTs/rules
• Uninstall should be explicit and safe (uninstall.php or register_uninstall_hook)

Read:

• references/lifecycle.md

3) Settings and admin UI (Settings API)

Prefer Settings API for options:

• register_setting(), add_settings_section(), add_settings_field()
• Sanitize via sanitize_callback

Read:

• references/settings-api.md

4) Security baseline (always)

Before shipping:

• Validate/sanitize input early; escape output late.
• Use nonces to prevent CSRF and capability checks for authorization.
• Avoid directly trusting $_POST / $_GET; use wp_unslash() and specific keys.
• Use $wpdb->prepare() for SQL; avoid building SQL with string concatenation.

Read:

• references/security.md

5) Custom Post Types and REST API (if needed)

• Register CPTs/taxonomies on init with show_in_rest for Gutenberg support.
• Follow REST API conventions: proper permission callbacks, schema, prepared statements.

Read:

• references/rest-api.md

6) Hooks and extensibility

• Add action hooks at key lifecycle points for extensibility.
• Use filters for modifiable output.
• Prefix all hook names with plugin slug.

Read:

• references/hooks.md

7) Cron and scheduled tasks (if needed)

• Schedule on activation, clear on deactivation.
• Critical: Never use same name for cron hook and internal do_action().
• Process large datasets in batches.

Read:

• references/cron.md

8) Internationalization

• Use proper text domain matching plugin slug.
• Load textdomain on plugins_loaded.
• Use translation functions: __(), _e(), _x(), _n().

Verification

• Plugin activates with no fatals/notices.
• Settings save and read correctly (capability + nonce enforced).
• Uninstall removes intended data (and nothing else).
• Run repo lint/tests (PHPUnit/PHPCS if present).
• Passes Plugin Check plugin (no errors).

Failure modes / debugging

• Activation hook not firing:
  • Hook registered incorrectly (not in main file scope), wrong main file path, or plugin is network-activated
• Settings not saving:
  • Settings not registered, wrong option group, missing capability, nonce failure
• Security regressions:
  • Nonce present but missing capability checks; or sanitized input not escaped on output
• Cron infinite recursion:
  • Same name used for cron hook and internal do_action() call

Read:

• references/debugging.md

Escalation

For canonical detail, consult the Plugin Handbook and security guidelines before inventing patterns.

• Plugin Developer Handbook
• Security Best Practices
• Settings API