HTML strip character filter

The html_strip character filter removes HTML tags, such as <div>, <p>, and <a>, from the input text and renders plain text. The filter can be configured to preserve certain tags or decode specific HTML entities, such as &nbsp;, into spaces.

Example: HTML analyzer

  1. GET /_analyze
  2. {
  3.   "tokenizer": "keyword",
  4.   "char_filter": [
  5.     "html_strip"
  6.   ],
  7.   "text": "<p>Commonly used calculus symbols include &alpha;, &beta; and &theta; </p>"
  8. }

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Using the HTML analyzer, you can convert the HTML character entity references into their corresponding symbols. The processed text would read as follows:

  1. Commonly used calculus symbols include α, β and θ

Example: Custom analyzer with lowercase filter

The following example query creates a custom analyzer that strips HTML tags and converts the plain text to lowercase by using the html_strip analyzer and lowercase filter:

  1. PUT /html_strip_and_lowercase_analyzer
  2. {
  3.   "settings": {
  4.     "analysis": {
  5.       "char_filter": {
  6.         "html_filter": {
  7.           "type": "html_strip"
  8.         }
  9.       },
  10.       "analyzer": {
  11.         "html_strip_analyzer": {
  12.           "type": "custom",
  13.           "char_filter": ["html_filter"],
  14.           "tokenizer": "standard",
  15.           "filter": ["lowercase"]
  16.         }
  17.       }
  18.     }
  19.   }
  20. }

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Testing html_strip_and_lowercase_analyzer

You can run the following request to test the analyzer:

  1. GET /html_strip_and_lowercase_analyzer/_analyze
  2. {
  3.   "analyzer": "html_strip_analyzer",
  4.   "text": "<h1>Welcome to <strong>OpenSearch</strong>!</h1>"
  5. }

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In the response, the HTML tags have been removed and the plain text has been converted to lowercase:

  1. welcome to opensearch!

Example: Custom analyzer that preserves HTML tags

The following example request creates a custom analyzer that preserves HTML tags:

  1. PUT /html_strip_preserve_analyzer
  2. {
  3.   "settings": {
  4.     "analysis": {
  5.       "char_filter": {
  6.         "html_filter": {
  7.           "type": "html_strip",
  8.           "escaped_tags": ["b", "i"]
  9.         }
  10.       },
  11.       "analyzer": {
  12.         "html_strip_analyzer": {
  13.           "type": "custom",
  14.           "char_filter": ["html_filter"],
  15.           "tokenizer": "keyword"
  16.         }
  17.       }
  18.     }
  19.   }
  20. }

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Testing html_strip_preserve_analyzer

You can run the following request to test the analyzer:

  1. GET /html_strip_preserve_analyzer/_analyze
  2. {
  3.   "analyzer": "html_strip_analyzer",
  4.   "text": "<p>This is a <b>bold</b> and <i>italic</i> text.</p>"
  5. }

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In the response, the italic and bold tags have been retained, as specified in the custom analyzer request:

  1. This is a <b>bold</b> and <i>italic</i> text.