the_content

Filters a post's content before it's shown. Use it to add or change text before or after the post body.

Type Filter
From WordPress
Since 0.71
Fired in wp-includes/post-template.php

When it fires

WordPress applies the_content when a theme calls the_content() and when the Post Content block renders, and also for feeds, REST API responses and automatic excerpts. Core's own filters run on it too: blocks are rendered at priority 9, paragraphs are added at 10 and shortcodes run at 11.

You receive the content as HTML and must return it, changed or not.

Parameters

Parameters
`$content`string	Content of the current post.

What to return

The content as an HTML string. Always return $content, even when you don't change it.

Example: Add a note after single blog posts

PHP

add_filter( 'the_content', function ( $content ) {
	if ( ! is_singular( 'post' ) || ! in_the_loop() || ! is_main_query() ) {
		return $content;
	}
	$note = sprintf(
		'<p class="post-note">%s</p>',
		esc_html__( 'Thanks for reading. Questions? Leave a comment below.', 'my-snippets' )
	);
	return $content . $note;
} );

Good to know

Check in_the_loop() and is_main_query() so your text isn't added to excerpts, sidebars or other posts shown on the page.
Nothing escapes your output for you. Escape any text or URLs you add.
Page builders and custom templates that don't call the_content() won't run this filter.