How to create custom fields in WordPress

Decide what information you need to store, where it belongs, and whether it is a single value or a collection. Examples include an event date, product reference, subtitle, rating, or external URL.

Use a clear, lowercase meta key such as event_date. Do not change the key later without migrating existing values, or the old data will appear to have disappeared.

For a simple field, open a post or page in the block editor. Select the three-dot Options menu, choose Preferences, open General, enable Custom fields under Advanced, and reload the editor. The Custom Fields panel then appears below the content area.

Enter a key, enter its value, and select Add Custom Field. This is fine for occasional metadata, but it gives editors a plain key/value interface and does not provide field validation, conditional display, repeaters, or a polished editing experience.

For a reusable editor field, add a meta box from a custom plugin or child theme. Hook a function to add_meta_boxes, call add_meta_box(), and render the input in its callback. The meta box is placed inside the normal post editing form, so it does not need its own submit button.

Limit the box to the post types that need it. Give the input a unique name, load its existing value with get_post_meta(), and use an appropriate HTML input type such as text, date, number, checkbox, or select.

Save the field from a save callback attached to save_post. Add a nonce with wp_nonce_field() when rendering the box, verify it with wp_verify_nonce(), check the user capability, and return during autosaves or revisions. The save_post action can run more than once for one update, so these checks matter.

Read only the expected value from $_POST. Unslash it, validate the allowed format, sanitise it with the function that matches its type, and save it with update_post_meta(). That function adds the key if it does not already exist. Do not trust raw form data, and do not process the entire request array.

If JavaScript, the block editor, or the REST API needs the value, register the key with register_post_meta() or register_meta(). Set the correct type, set single according to whether one or several values are returned, and add a sanitisation callback where necessary.

Set show_in_rest only when the value should be available through the REST API. The post type must support custom-fields, and array values need an appropriate REST schema. Exposing a field without considering permissions can make private data readable or writable, so use an authorisation callback for restricted values.

Retrieve a single value with get_post_meta( $post_id, 'event_date', true ). Escape it at the point of output: use esc_html() for visible text, esc_attr() for an HTML attribute, esc_url() for a URL, and an appropriate escaping method for other contexts. Sanitising on save does not replace escaping on output.

For more than basic post metadata, Meta Box AIO is a practical shortcut. It provides a visual field and meta-box builder with multiple field types, conditional logic, custom post type and taxonomy support, and integrations. Use it when hand-built boxes would create too much maintenance, but keep the same rules for field naming, access control, validation, and output.