XLSForm Constraint Examples (Copy & Paste)

XLSForm constraints validate an answer the moment it is entered using the constraint column, rejecting impossible values like a negative age or a future birth date. This guide gives you copy-paste constraint examples for the validations field surveys need most.

After adding a constraint, follow the XLSForm validation checklist to test visible paths, device behavior, and the exported result.

A constraint is a rule the answer must satisfy. If it fails, ODK shows your constraint_message and refuses to advance until the answer is fixed. This is how you keep bad data out of your dataset at the source — far more reliable than cleaning it later.

How does the constraint column work?

Add two columns to your survey sheet: constraint (the rule) and constraint_message (what the enumerator sees if it fails). Inside the rule, a single dot . refers to the current question's answer.

type	name	label	constraint	constraint_message
integer	age	What is your age?	. >= 0 and . <= 120	Age must be between 0 and 120

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If someone types 250, ODK blocks it and shows "Age must be between 0 and 120". Below are ready-to-use rules for common cases — copy the constraint and constraint_message straight into your form.

Number range constraints

Keep numeric answers inside a plausible range:

type	name	label	constraint	constraint_message
integer	age	Age of respondent	. >= 0 and . <= 120	Age must be between 0 and 120
integer	household	Household size	. >= 1 and . <= 30	Household size must be 1 to 30
decimal	price	Price paid (USD)	. >= 0	Price cannot be negative

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Phone number and text constraints

Use regex() to enforce a text pattern, such as a 10-digit phone number:

type	name	label	constraint	constraint_message
text	phone	Phone number	regex(.	'^[0-9]{10}$')
text	id_code	National ID	regex(.	'^[A-Z]{2}[0-9]{6}$')

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The string-length() function constrains length without a full pattern:

type	name	label	constraint	constraint_message
text	pin	4-digit PIN	string-length(.) = 4	PIN must be exactly 4 characters

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Date constraints

Stop future dates or unrealistic ones using today():

type	name	label	constraint	constraint_message
date	dob	Date of birth	. <= today()	Date of birth cannot be in the future
date	visit	Visit date	. <= today() and . >= '2026-01-01'	Visit date must be in 2026 up to today

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Cross-question constraints

A constraint can reference another answer with ${name} — for example, an end date that cannot precede a start date:

type	name	label	constraint	constraint_message
date	start_date	Start date
date	end_date	End date	. >= ${start_date}	End date must be on or after the start date

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Select-question constraints

Limit how many options a respondent may choose in a select_multiple question with count-selected():

type	name	label	constraint	constraint_message
select_multiple symptoms	symptoms	Select up to 3 symptoms	count-selected(.) <= 3	Choose no more than 3 symptoms

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Why constraints matter in the field

Constraints are your first and cheapest line of data-quality defense. They block impossible values before they enter the dataset, cut hours of post-survey cleaning, and reduce the back-and-forth of re-contacting respondents to fix errors. Combined with an audit log, validated answers give you data you can trust on day one rather than at endline.

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