Validate JSON payloads against a schema with detailed error messages (no AI)

What is this?

A modular schema checker that returns detailed error messages on validation failure.

Stop your workflows from breaking due to bad input. This subworkflow validates incoming JSON against a schema you define and returns clear, human readable errors before anything has the chance to break.

The most common use: a webhook receives data, you validate it, and either continue or return a 400 with exactly what was wrong. This is how production APIs handle input validation, and this template brings that same reliability to webhooks in n8n.

Works anywhere you need to check data: webhook payloads, form submissions, API requests, or LLM outputs.

Supports: type checks, required fields, enums, regex patterns, numeric ranges, array constraints, conditional logic (oneOf / anyOf / allOf), and rejection of unknown fields.

Why use this?

Bad input breaks workflows and is a nightmare to debug. This catches it upfront so you can error fast, fail safe, and return useful messages instead of breaking down.