Using regular expressions in XLSForm

Last updated: 21 Mar 2026

A regular expression, or regex, is a search pattern used to match specific characters or character ranges within text. Regular expressions are commonly used to validate, search, extract, or restrict text input.

In KoboToolbox, regular expressions are typically used to control how users enter data. For example, you can restrict a mobile number to exactly 10 digits, enforce a specific ID format, or limit text to uppercase letters only.

This article provides an overview of common regular expression components and practical examples you can use to validate and restrict text input in your forms.

To learn more about using regular expressions in your forms, see Introduction to form logic in XLSForm and Introduction to form logic in the Formbuilder.

Common regex components

Regular expressions in KoboToolbox are written inside the regex() function. For example, regex(., '^[0-9]{10}$') restricts an input to exactly 10 digits.

The following tables describe commonly used regex elements.

Anchors and grouping

Regex	Description
^	Matches the start of a string
$	Matches the end of a string
( )	Groups characters together
|	Matches one pattern or another (logical OR)

Character classes

Regex	Description
[abc]	Matches a, b, or c
[a-z]	Matches any lowercase letter
[A-Z]	Matches any uppercase letter
[0-9]	Matches any digit from 0 to 9
[a-zA-Z0-9]	Matches letters or digits
[^abc]	Matches any character except a, b, or c
[^A-Z]	Matches any character except uppercase letters

Special character shortcuts

Regex	Description
\d	Matches any digit (same as [0-9])
\D	Matches any non-digit
\w	Matches any word character (letters, digits, _)
\W	Matches any non-word character
\s	Matches a space or tab
\b	Matches a word boundary
.	Matches a literal dot (.)
\@	Matches a literal @
\$	Matches a literal $
\\	Matches a literal backslash (\)
\number	Refers to a previously matched group

Quantifiers

Regex	Description
?	Matches zero or one occurrence
*	Matches zero or more occurrences
+	Matches one or more occurrences
{x}	Matches exactly x occurrences
{x,}	Matches at least x occurrences
{x,y}	Matches between x and y occurrences

Common examples

The following examples can be used as constraints or validation criteria in your forms.

Common regex expressions with numbers

Regex	Description
regex(., ‘^\d+$’)	Limit input to numbers
regex(., ‘^\d{2}$’)	Limit input to 2 digits
regex(., ‘^\d{2,4}$’)	Limit input to 2-4 digits
regex(., ‘^\d{10}$’)	Limit input to 10 digits
regex(., ‘^[1-9][0-9]?$|^100$’)	Limit input to a number between 1 and 100 (e.g., for a percentage)
regex(., ‘^[1-9][0-9]{8}$’)	Limit input to 9 digits, first digit cannot be 0
regex(., ‘^\d{2}.\d{3}$’)	Limit input to number formatted as 12.345
regex(., ‘^(\d{10}|\d{13}|\d{17})$’)	Limit input to 10, 13, or 17 digits
regex(., ‘^(12|345)$’)	Input must be 12 or 345

Common regex expressions with letters

Regex	Description
regex(., ‘^\D*$’)	Limit input to letters, spaces, and symbols (no numbers)
regex(., ‘^[A-Za-z]+$’)	Limit input to letters
regex(., ‘^[A-Za-z\s]+$’)	Limit input to letters and spaces
regex(., ‘^[a-z]{1,6}$’)	Limit input to 1–6 lowercase letters
regex(., ‘^[A-Z]{1,10}$’)	Limit input to 1–10 uppercase letters
regex(., ‘^(Apple|Orange|Banana)$’)	Input must match one word from the list
regex(., ‘^colou?r$’)	Allows color or colour
regex(., ‘^[A-Z\s]+$’)	Limit input to uppercase letters and spaces only
regex(., ‘^[a-z_]+$’)	Limit input to lowercase letters and underscores (_)

Common regex expressions with letters and numbers

Regex	Description
regex(., ‘^\w{3}$’)	Limit input to exactly 3 letters, digits, or underscores (_)
regex(., ‘^[A-Z]{1}[0-9]{8}$’)	Limit input to one letter and eight numbers
regex(., ‘^CAR-PRC-2020-\d{4}$’)	Limit input to a specific ID format
regex(., ‘^\W*(\w+\b\W*){3}$’)	Limit input to exactly 3 words
regex(., ‘^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*(\.[a-zA-Z0-9]+(-[a-zA-Z0-9]+)*)*\.[a-zA-Z]{2,}$’)	Limit input to common email format

For additional help building and testing patterns, visit: http://www.regexr.com/