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 and placeholder support in $wpdb->prepare()).

Procedure

0) Triage and locate plugin entrypoints

1. Run triage:
   • node skills/​wp-project-triage/​scripts/​detect_wp_project.mjs
2. Detect plugin headers (deterministic scan):
   • node skills/​wp-plugin-development/​scripts/​detect_plugins.mjs

If this is a full site repo, pick the specific plugin under wp-content/​plugins/ or mu-plugins/ before changing code.

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.

See:

• 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)

See:

• 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

See:

• 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.

See:

• references/​security.md

5) Data storage, cron, migrations (if needed)

• Prefer options for small config; custom tables only if necessary.
• For cron tasks, ensure idempotency and provide manual run paths (WP-CLI or admin).
• For schema changes, write upgrade routines and store schema version.

See:

• references/​data-and-cron.md

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) and any JS build steps if the plugin ships assets.

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

See:

• references/​debugging.md

Escalation

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