elasticsearch/docs/reference/text-analysis/analysis-stemmer-tokenfilter.md

---

navigation_title: "Stemmer" mapped_pages:

• https://www.elastic.co/guide/en/elasticsearch/reference/current/analysis-stemmer-tokenfilter.html ---

Stemmer token filter [analysis-stemmer-tokenfilter]

Provides algorithmic stemming for several languages, some with additional variants. For a list of supported languages, see the language parameter.

When not customized, the filter uses the porter stemming algorithm for English.

Example [analysis-stemmer-tokenfilter-analyze-ex]

The following analyze API request uses the stemmer filter’s default porter stemming algorithm to stem the foxes jumping quickly to the fox jump quickli:

GET /_analyze
{
  "tokenizer": "standard",
  "filter": [ "stemmer" ],
  "text": "the foxes jumping quickly"
}

The filter produces the following tokens:

[ the, fox, jump, quickli ]

Add to an analyzer [analysis-stemmer-tokenfilter-analyzer-ex]

The following create index API request uses the stemmer filter to configure a new custom analyzer.

PUT /my-index-000001
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "whitespace",
          "filter": [ "stemmer" ]
        }
      }
    }
  }
}

Configurable parameters [analysis-stemmer-tokenfilter-configure-parms]

$$$analysis-stemmer-tokenfilter-language-parm$$$

language: (Optional, string) Language-dependent stemming algorithm used to stem tokens. If both this and the name parameter are specified, the language parameter argument is used.

:::{dropdown} Valid values for language

Valid values are sorted by language. Defaults to english. Recommended algorithms are bolded. Arabic: arabic Armenian: armenian Basque: basque Bengali:bengali Brazilian Portuguese:brazilian Bulgarian:bulgarian Catalan:catalan Czech:czech Danish:danish Dutch:dutch, dutch_kp [8.16.0] English:english, light_english, lovins [8.16.0], minimal_english, porter2, possessive_english Estonian:estonian Finnish:finnish, light_finnish French:light_french, french, minimal_french Galician:galician, minimal_galician (Plural step only) German:light_german, german, minimal_german Greek:greek Hindi:hindi Hungarian:hungarian, light_hungarian Indonesian:indonesian Irish:irish Italian:light_italian, italian Kurdish (Sorani):sorani Latvian:latvian Lithuanian:lithuanian Norwegian (Bokmål):norwegian, light_norwegian, minimal_norwegian Norwegian:(Nynorsk)light_nynorsk, minimal_nynorsk Persian:persian Portuguese:light_portuguese, minimal_portuguese, portuguese, portuguese_rslp Romanian:romanian Russian:russian, light_russian Serbian:serbian Spanish:light_spanish, spanish spanish_plural Swedish:swedish, light_swedish Turkish:turkish :::

name: An alias for the language parameter. If both this and the language parameter are specified, the language parameter argument is used.

Customize [analysis-stemmer-tokenfilter-customize]

To customize the stemmer filter, duplicate it to create the basis for a new custom token filter. You can modify the filter using its configurable parameters.

For example, the following request creates a custom stemmer filter that stems words using the light_german algorithm:

PUT /my-index-000001
{
  "settings": {
    "analysis": {
      "analyzer": {
        "my_analyzer": {
          "tokenizer": "standard",
          "filter": [
            "lowercase",
            "my_stemmer"
          ]
        }
      },
      "filter": {
        "my_stemmer": {
          "type": "stemmer",
          "language": "light_german"
        }
      }
    }
  }
}