﻿---
title: normalizer
description: The normalizer property of keyword fields is similar to analyzer except that it guarantees that the analysis chain produces a single token. The normalizer...
url: https://www.elastic.co/elastic/docs-builder/docs/2642/reference/elasticsearch/mapping-reference/normalizer
products:
  - Elasticsearch
applies_to:
  - Elastic Cloud Serverless: Generally available
  - Elastic Stack: Generally available
---

# normalizer
The `normalizer` property of [`keyword`](https://www.elastic.co/elastic/docs-builder/docs/2642/reference/elasticsearch/mapping-reference/keyword) fields is similar to [`analyzer`](https://www.elastic.co/elastic/docs-builder/docs/2642/reference/elasticsearch/mapping-reference/analyzer) except that it guarantees that the analysis chain produces a single token.
The `normalizer` is applied prior to indexing the keyword, as well as at search-time when the `keyword` field is searched via a query parser such as the [`match`](https://www.elastic.co/elastic/docs-builder/docs/2642/reference/query-languages/query-dsl/query-dsl-match-query) query or via a term-level query such as the [`term`](https://www.elastic.co/elastic/docs-builder/docs/2642/reference/query-languages/query-dsl/query-dsl-term-query) query.
A simple normalizer called `lowercase` ships with elasticsearch and can be used. Custom normalizers can be defined as part of analysis settings as follows.
```json

{
  "settings": {
    "analysis": {
      "normalizer": {
        "my_normalizer": {
          "type": "custom",
          "char_filter": [],
          "filter": ["lowercase", "asciifolding"]
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "foo": {
        "type": "keyword",
        "normalizer": "my_normalizer"
      }
    }
  }
}


{
  "foo": "BÀR"
}


{
  "foo": "bar"
}


{
  "foo": "baz"
}




{
  "query": {
    "term": {
      "foo": "BAR"
    }
  }
}


{
  "query": {
    "match": {
      "foo": "BAR"
    }
  }
}
```

The above queries match documents 1 and 2 since `BÀR` is converted to `bar` at both index and query time.
```json
{
  "took": $body.took,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped" : 0,
    "failed": 0
  },
  "hits": {
    "total" : {
        "value": 2,
        "relation": "eq"
    },
    "max_score": 0.4700036,
    "hits": [
      {
        "_index": "index",
        "_id": "1",
        "_score": 0.4700036,
        "_source": {
          "foo": "BÀR"
        }
      },
      {
        "_index": "index",
        "_id": "2",
        "_score": 0.4700036,
        "_source": {
          "foo": "bar"
        }
      }
    ]
  }
}
```

Also, the fact that keywords are converted prior to indexing also means that aggregations return normalized values:
```json

{
  "size": 0,
  "aggs": {
    "foo_terms": {
      "terms": {
        "field": "foo"
      }
    }
  }
}
```

returns
```json
{
  "took": 43,
  "timed_out": false,
  "_shards": {
    "total": 1,
    "successful": 1,
    "skipped" : 0,
    "failed": 0
  },
  "hits": {
    "total" : {
        "value": 3,
        "relation": "eq"
    },
    "max_score": null,
    "hits": []
  },
  "aggregations": {
    "foo_terms": {
      "doc_count_error_upper_bound": 0,
      "sum_other_doc_count": 0,
      "buckets": [
        {
          "key": "bar",
          "doc_count": 2
        },
        {
          "key": "baz",
          "doc_count": 1
        }
      ]
    }
  }
}
```


## Synthetic source

<applies-to>
  - Elastic Cloud Serverless: Generally available
  - Elastic Stack: Generally available since 9.3
</applies-to>

When [synthetic source](/elastic/docs-builder/docs/2642/reference/elasticsearch/mapping-reference/mapping-source-field#synthetic-source) is enabled on an index, keyword fields with a normalizer store the original pre-normalized value separately so that it can be included in the synthetic source. This can cause elevated disk usage since values are stored twice: once pre-normalized, and once normalized.
To reduce disk usage, the `normalizer_skip_store_original_value` mapping parameter can be set to `true`. When enabled, the original value is not stored, and the normalized value is used in the reconstructed source instead.
For custom normalizers, this parameter defaults to `false`. However, for the built-in `lowercase` normalizer, it defaults to `true`.