Custom Mask Expressions in Droplet let you define exactly how a user’s input should be structured in an Input (Single Line) component. By restricting allowable characters and formatting patterns, you can ensure cleaner, more consistent data in your forms.
When Should I Use a Custom Mask?
Masks in Droplet help ensure consistent, valid data entry. For instance, if you want a user to enter a specific number of digits (like a phone number) or strictly allow letters only (like a middle initial), custom masks let you define rules that enforce the exact format and type of characters entered.
Typically, you’d use a custom mask when:
You want to limit or validate input character-by-character in a single-line text field.
None of the Built-in Masks (like phone number, SSN, ZIP code) fit your use-case.
In essence, a custom mask is your go-to tool when you want to control exactly how input gets typed.
/9
Numeric character placeholder (0-9)
Numeric character placeholder (0-9)
Example Use
Accepts exactly 4 digits (like a year).
/a
Alphabetic character placeholder (A-Z, a-z)
Alphabetic character placeholder (A-Z, a-z)
Example Use
Accepts exactly 1 letter (like a middle initial).
/*
Alpha-numeric placeholder (letters or digits)
Alpha-numeric placeholder (letters or digits)
Example Use
Accepts exactly 15 alpha-numeric characters (e.g., Batch ID).
/l
Lowercase character placeholder
Lowercase character placeholder
Example Use
Accepts exactly 2 lowercase letters.
/u
Uppercase character placeholder
Uppercase character placeholder
Example Use
Accepts exactly 3 uppercase letters.
/?
Any character placeholder (a wildcard)
Any character placeholder (a wildcard)
Example Use
Accepts exactly 2 characters, then a dash, then exactly 3 characters. No restriction on letters, digits, etc.
Literal Characters
Certain characters appear exactly as typed — they are not placeholders. These can be letters, numbers, punctuation, parentheses, dashes, dots, etc.
Examples:
3, G,
Certain characters appear exactly as typed — they are not placeholders. These can be letters, numbers, punctuation, parentheses, dashes, dots, etc.
Examples:
3, G,
-, (, ), ., :, /Example Use
This mask accepts 3 numeric digits, but must begin with ABC- first (e.g. ABC-123 or ABC-456).
User-Defined Sets
Lets you specify exactly which characters are allowed. Use square brackets to define your set.
Lets you specify exactly which characters are allowed. Use square brackets to define your set.
Example Use
Accepts only letters
a, b, c, d and digits 1, 2, 3 in a single slot.Ranges
Specify exact or variable lengths using parentheses. You can do exact or min:max.
Specify exact or variable lengths using parentheses. You can do exact or min:max.
Example Uses
Exactly three digits.
Accepts between 2 and 3 digits. Perfect for optional digit lengths (e.g.,
99 or 999).NOT Operator (!)
Exclude certain characters or sets with
Exclude certain characters or sets with
!2 Exceptions
Cannot use the NOT operator with ranges or with the wildcard (for example, /!? is invalid).
Cannot use the NOT operator with ranges or with the wildcard (for example, /!? is invalid).
Example Use
Three characters, each must not be a digit. Could be letters, punctuation, etc. (e.g.,
XYZ, !!!, but not 123).Was this article helpful?
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