---
type: "fhirpath-function"
title: "FHIRPath Function: lower"
function: "lower"
category: "String Manipulation"
section: "5.6.8"
source: "fhirpath/functions.json"
---
# FHIRPath Function: lower
Returns the input string with all characters converted to lower case.

If the input collection is empty, the result is empty.

If the input collection contains multiple items, the evaluation of the expression will end and signal an error to the calling environment.

``` fhirpath
'ABCDEFG'.lower() // 'abcdefg'
'aBcDEFG'.lower() // 'abcdefg'
```
## Summary
- **Category**: String Manipulation
- **Section**: `5.6.8`
- **Return Type**: `String`
- **Empty Input Result**: `empty`
- **Errors on Multiple Input**: `true`
## Description
Returns the input string with all characters converted to lower case.
## Arguments
- none
## Type Mapping
- `String-String`
## Example
```fhirpath
'ABCDEFG'.lower() // 'abcdefg'
'aBcDEFG'.lower() // 'abcdefg'
```