---
title: Character filter reference
description: Character filters are used to preprocess the stream of characters before it is passed to the tokenizer. A character filter receives the original text...
url: https://www.elastic.co/elastic/docs-builder/docs/3028/reference/text-analysis/character-filter-reference
products:
  - Elasticsearch
---

# Character filter reference
*Character filters* are used to preprocess the stream of characters before it is passed to the [tokenizer](https://www.elastic.co/elastic/docs-builder/docs/3028/reference/text-analysis/tokenizer-reference).
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 [custom analyzers](https://docs-v3-preview.elastic.dev/elastic/docs-builder/docs/3028/manage-data/data-store/text-analysis/create-custom-analyzer).
<definitions>
  <definition term="HTML Strip Character Filter">
    The `html_strip` character filter strips out HTML elements like `<b>` and decodes HTML entities like `&amp;`.
  </definition>
  <definition term="Mapping Character Filter">
    The `mapping` character filter replaces any occurrences of the specified strings with the specified replacements.
  </definition>
  <definition term="Pattern Replace Character Filter">
    The `pattern_replace` character filter replaces any characters matching a regular expression with the specified replacement.
  </definition>
</definitions>