PHP: Remove all HTML Tags from String

Sometimes, it is necessary to remove all HTML tags and formatting from a text. In other words, to extract the plain text from a formatted HTML document.

In this tutorial, I would like to show you, how you can do it. We are using the PHP function strip-tags() for this purpose.

Remove all of the Formatting

Let us look at a small example firs

$txt = "<p>This is a <b>text</b>.</p>";

$txt = strip_tags($txt);  // This is a text.

We are storing a string with some HTML formattings into the variable $txt. After we have applied strip_tags() to this text, all of the formatting is vanished.

Strip HTML Comments

Incidentally, strip_tags() is also deleting all HTML comments that are possibly located in the passed string.

$txt = "<p>AB<!-- Comment -->CD</p>";

$txt = strip_tags($txt);  // ABCD

As you can see in this example, only "ABCD" remains in the string.

Keep some of the Formatting

The second parameter of strip_tags() is optional. You can use this parameter to pass a collection of HTML tags that should not be deleted.

$txt = "<p>This is a <b>text</b>.</p>";

$txt = strip_tags($txt,'<p><h1>');  // <p>This is a text.</p>

In this example, we would like to keep paragraphs (<p>) and headings (<h1>) in the string while the rest should be sorted out. Accordingly, only the <b> tag will be removed in the example above.

Security Advice

Finally, I would like to make a few words about the security when using strip_tags(). It is not automatically ensured that you can use this function to make a user input "secure". For example, when allowing the <p> tag and someone is submitting something like <p onmouseover="do_evil_code">, this is not removed by strip_tags(). Generally, strip_tags() is not removing any attributes from allowed HTML tags.

Furthermore, it can cause problems when passing invalid, incorrect or incomplete HTML code to this function. Under circumstances, this can lead to more deleted text than intended.

You can read some more information about this in the answers to the question about how to allow only specific HTML code.