HTML Tidy  5.1.25
The HTACG Tidy HTML Project
Featured Options

Overview of popular features and problems

Indenting output for readability

Indenting the source markup of an HTML document makes the markup easier to read. Tidy can indent the markup for an HTML document while recognizing elements whose contents should not be indented. In the example below, Tidy indents the output while preserving the formatting of the <pre> element:


1 <html>
2  <head>
3  <title>Test document</title>
4  </head>
5  <body>
6  <p>This example shows how Tidy can indent output while preserving
7  formatting of particular elements.</p>
9  <pre>This is
10  <em>genuine
11  preformatted</em>
12  text
13  </pre>
14  </body>
15  </html>


1 <html>
2  <head>
3  <title>Test document</title>
4  </head>
6  <body>
7  <p>This example shows how Tidy can indent output while preserving
8  formatting of particular elements.</p>
9 <pre>
10 This is
11 <em>genuine
12  preformatted</em>
13  text
14 </pre>
15  </body>
16 </html>

Tidy’s indenting behavior is not perfect and can sometimes cause your output to be rendered by browsers in a different way than the input. You can avoid unexpected indenting-related rendering problems by setting indent:no or indent:auto in a config file.

Preserving original indenting not possible

Tidy is not capable of preserving the original indenting of the markup from the input it receives. That’s because Tidy starts by building a clean parse tree from the input, and that parse tree doesn’t contain any information about the original indenting. Tidy then pretty-prints the parse tree using the current config settings. Trying to preserve the original indenting from the input would interact badly with the repair operations needed to build a clean parse tree, and would considerably complicate the code.

Encodings and character references

Tidy defaults to assuming you want output to be encoded in UTF-8. But Tidy offers you a choice of other character encodings: US ASCII, ISO Latin-1, and the ISO 2022 family of 7 bit encodings.

Tidy doesn’t yet recognize the use of the HTML <meta> element for specifying the character encoding.

The full set of HTML character references are defined. Cleaned-up output uses named character references for characters when appropriate. Otherwise, characters outside the normal range are output as numeric character references.


Tidy offers advice on potential accessibility problems for people using non-graphical browsers.

Cleaning up presentational markup

Some tools generate HTML with presentational elements such as <font>, <nobr>, and <center>. Tidy’s -clean option will replace those elements with <style> elements and CSS.

Some HTML documents rely on the presentational effects of <p> start tags that are not followed by any content. Tidy deletes such <p> tags (as well as any headings that don’t have content). So do not use <p> tags simply for adding vertical whitespace; instead use CSS, or the <br> element. However, note that Tidy won’t discard <p> tags that are followed by any non-breaking space (that is, the


named character reference).

Teaching Tidy about new tags

You can teach Tidy about new tags by declaring them in the configuration file, the syntax is:

new-inline-tags: tag1, tag2, tag3
new-empty-tags: tag1, tag2, tag3
new-blocklevel-tags: tag1, tag2, tag3
new-pre-tags: tag1, tag2, tag3

The same tag can be defined as empty and as inline, or as empty and as block.

These declarations can be combined to define a new empty inline or empty block element, but you are not advised to declare tags as being both inline and block.

Note that the new tags can only appear where Tidy expects inline or block-level tags respectively. That means you can’t place new tags within the document head or other contexts with restricted content models.

Ignoring PHP, ASP, and JSTE instructions

Tidy will gracefully ignore many cases of PHP, ASP, and JSTE instructions within element content and as replacements for attributes, and preserve them as-is in output; for example:

<option <% if rsSchool.Fields("ID").Value
= session("sessSchoolID")
then Response.Write("selected") %>

But note that Tidy may report missing attributes when those are “hidden” within the PHP, ASP, or JSTE code. If you use PHP, ASP, or JSTE code to create a start tag, but place the end tag explicitly in the HTML markup, Tidy won’t be able to match them up, and will delete the end tag. In that case you are advised to make the start tag explicit and to use PHP, ASP, or JSTE code for just the attributes; for example:

<a href="<>">do you feel lucky?</a>

Tidy can also get things wrong if the PHP, ASP, or JSTE code includes quotation marks; for example:


Tidy will see the quotation mark preceding ID as ending the attribute value, and proceed to complain about what follows.

Tidy allows you to control whether line wrapping on spaces within PHP, ASP, and JSTE instructions is enabled; see the wrap-php, wrap-asp, and wrap-jste config options.

Correcting well-formedness errors in XML markup

Tidy can help you to correct well-formedness errors in XML markup. Tidy doesn’t yet recognize all XML features, though; for example, it doesn’t understand CDATA sections or DTD subsets.