[[analysis-charfilters]]
== Character filters reference

_Character filters_ are used to preprocess the stream of characters before it
is passed to the <<analysis-tokenizers,tokenizer>>.

A character filter receives the original text as a stream of characters and
can transform the stream by adding, removing, or changing characters.  For
instance, a character filter could be used to convert Hindu-Arabic numerals
(٠‎١٢٣٤٥٦٧٨‎٩‎) into their Arabic-Latin equivalents (0123456789), or to strip HTML
elements like `<b>` from the stream.


Elasticsearch has a number of built in character filters which can be used to build
<<analysis-custom-analyzer,custom analyzers>>.

<<analysis-htmlstrip-charfilter,HTML Strip Character Filter>>::

The `html_strip` character filter strips out HTML elements like `<b>` and
decodes HTML entities like `&amp;`.

<<analysis-mapping-charfilter,Mapping Character Filter>>::

The `mapping` character filter replaces any occurrences of the specified
strings with the specified replacements.

<<analysis-pattern-replace-charfilter,Pattern Replace Character Filter>>::

The `pattern_replace` character filter replaces any characters matching a
regular expression with the specified replacement.

include::charfilters/htmlstrip-charfilter.asciidoc[]

include::charfilters/mapping-charfilter.asciidoc[]

include::charfilters/pattern-replace-charfilter.asciidoc[]
