Elasticsearch allows you to configure a text scoring algorithm or similarity per field. The similarity setting provides a simple way of choosing a text similarity algorithm other than the default BM25, such as boolean.

Only text-based field types like text and keyword support this configuration.

Custom similarities can be configured by tuning the parameters of the built-in similarities. For more details about this expert options, see the similarity module.

The only similarities which can be used out of the box, without any further configuration are:

The similarity can be set on the field level when a field is first created, as follows:

PUT my-index-000001
{
  "mappings": {
    "properties": {
      "default_field": { 
        "type": "text"
      },
      "boolean_sim_field": {
        "type": "text",
        "similarity": "boolean" 
      }
    }
  }
}