WordPress Bootstrap Hooks Explained: Why Timing Determines Success or Failure

In WordPress development, calling functions in the wrong bootstrap hook can cause silent failures or fatal errors, even when the code itself is syntactically correct. For example, registering a post type during plugins_loaded triggers errors because taxonomies are not yet available, while adding theme support during init is silently ignored because that window has already closed. WordPress provides five key hooks in a strict sequence — muplugins_loaded, plugins_loaded, after_setup_theme, init, and wp_loaded — each designed for a specific class of actions. These timing bugs are notoriously difficult to diagnose because symptoms, such as missing thumbnails or broken translations, often appear unrelated to their root cause. Understanding which hook is open at each stage of the WordPress lifecycle is essential to writing reliable, predictable plugin and theme code.