Validator

Server Source code Package

Validates events using JSON Schema with two modes: format (structure) and contract (business rules).

Setup

Integrated

Install the package:

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Configure in your code:

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Bundled

Add to your flow.json:

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See Bundled Mode setup → | CLI reference →

Validation modes

Mode	Purpose
format	Validates full WalkerOS.Event structure
contract	Validates entity/action-specific business rules

Logger levels

Level	Output
ERROR	Validation failures only
DEBUG	All validation results (pass and fail)

Configuration

Property	Type	Description	More
format	boolean	Validate full WalkerOS.Event structure. Pre-compiled at init.
contract	object	Event-specific validation rules. Entity/action keyed, supports wildcards.

Option	Type	Default	Description
format	boolean	true	Validate full WalkerOS.Event structure
contract	Contract	-	Entity/action keyed validation rules

Behavior

When validation fails

Invalid events are dropped from the pipeline and do not reach destinations. The validator logs detailed error information:

Validation	Log message	Includes
Format	Event format invalid	Field-level errors from AJV
Contract	Contract validation failed	Rule name + field-level errors

Example log output:

[ERROR] Event format invalid { errors: "data/name must match pattern \"^\\w+ \\w+$\"" }
[ERROR] Contract validation failed { rule: "product add", errors: "data must have required property 'id'" }

When validation passes

• Format valid: Event continues to contract validation (if configured)
• Contract valid: Logs debug message, event continues to next transformer or destinations
• No matching contract: Event passes through unchanged (validation is opt-in per entity/action)

Pipeline flow

Event → Format check → Contract check → Next transformer/Destination
             ↓                ↓
          Invalid?         Invalid?
             ↓                ↓
        Drop + Log       Drop + Log

Conditional rules

Apply different schemas based on event data:

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Wildcard patterns

Match multiple events with wildcards:

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Next steps

• Create your own - Build custom transformers