Debug Template Validation Errors

Template errors can prevent document generation or produce unexpected output. This guide helps you identify and resolve common template validation errors.

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Enabling Error Display

Inline Errors (Recommended for Development)

Enable “Inline template syntax errors” in the Build a Doc action:

• Errors appear in the output document instead of failing the action
• Helps identify exactly where errors occur
• Useful during template development

Error Messages

When inline errors are disabled, errors are returned in the action failure response.

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Common Syntax Errors

Missing Closing Brackets

Error: Unexpected end of tag

Cause: Tag not properly closed

Wrong:

<<[CustomerName>

Correct:

<<[CustomerName]>>

Note

For complete syntax rules and examples, see the Word Template Syntax reference.

Unclosed Loops

Error: Unclosed foreach block

Cause: Missing <</foreach>> tag

Wrong:

<<foreach [item in Items]>>
<<[item.Name]>>

Correct:

<<foreach [item in Items]>>
<<[item.Name]>>
<</foreach>>

Unclosed Conditionals

Error: Unclosed if block

Cause: Missing <</if>> tag

Wrong:

<<if [ShowDiscount]>>
Discount applied

Correct:

<<if [ShowDiscount]>>
Discount applied
<</if>>

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Data Binding Errors

Invalid Property Path

Error: Invalid path: 'Custmer.Name'

Cause: Typo in property name or path doesn’t exist

Fix: Verify the path matches your JSON structure exactly (case-sensitive)

Note

To understand how data binding works, see templates and data binding.

Null Reference

Error: Null reference at 'Customer.Address.City'

Cause: Parent object is null

Fix: Ensure data is populated, and add null checks or ensure data is populated:

<<if [Customer.Address]>><<[Customer.Address.City]>><</if>>

Type Mismatch

Error: Cannot convert 'string' to 'number'

Cause: Attempting numeric operations on string values

Fix: Ensure data types match expected operations

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Loop Errors

Invalid Iterator

Error: Invalid iterator expression

Cause: Malformed foreach syntax

Wrong:

<<foreach [Items]>>

Correct:

<<foreach [item in Items]>>

Array Not Found

Error: 'Items' is not an array

Cause: Property is not an array or doesn’t exist

Fix: Verify the property exists and is an array in your data source

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Debugging Techniques

Step 1: Isolate the Problem

1. Remove complex sections temporarily
2. Test with minimal template
3. Add sections back gradually to find the issue

Step 2: Validate JSON Data

1. Use a JSON validator tool
2. Ensure structure matches template expectations (see Structure JSON Data)
3. Check for special characters that might need escaping

Step 3: Check Property Paths

1. List all placeholders in your template
2. Verify each path exists in your JSON
3. Check capitalisation matches exactly

Step 4: Test in Add-in

1. Use the Word Add-in preview feature
2. Errors display immediately
3. Faster iteration than full Power Automate testing

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Error Reference Table

Error	Cause	Solution
Unexpected end of tag	Missing >>	Close all tags with >>
Unclosed foreach block	Missing <</foreach>>	Add closing foreach tag
Unclosed if block	Missing <</if>>	Add closing if tag
Invalid path	Property doesn’t exist	Check spelling and structure
Null reference	Parent object is null	Add null checks
Type mismatch	Wrong data type	Verify data types
Invalid expression	Syntax error in expression	Check expression syntax

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Prevention Tips

1. Use consistent naming - Follow a naming convention for properties
2. Validate data first - Check data structure before template processing
3. Test incrementally - Don’t wait until the end to test
4. Keep templates simple - Break complex logic into data preparation
5. Use version control - Track template changes

Tip

Create a template testing checklist and use it before deploying templates to production.

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Related Topics

• Structure JSON Data
• Author Advanced Word Templates
• Word Template Syntax
• Handle Errors in Flows