Contract preflight
Checks one sanitized payload against explicit top-level field rules before the data enters an automation.
Day 051 / n8n / Workflow Automation
Workflow Input Validator
/ Overview
A dependency-free Python CLI that checks a sanitized workflow payload against a small declarative contract before automation begins.
Webhook and form payloads can reach an automation with missing fields, unexpected types or extra data. A small preflight check needs to make those mismatches visible without executing a workflow or copying payload values into routine reports.
/ Provided servicesClear thinking.
Clear thinking.
Practical delivery.
Bounded validation
Limits file size, field count, names, rule keys and collection sizes while rejecting malformed contracts.
Data-minimized reporting
Reports field names, generic issue codes and counts without echoing supplied payload values.
/ Solution
Workflow Input Validator loads one bounded local contract and one bounded local payload, rejects duplicate JSON keys, and checks required fields, supported types, string and array limits, allowlisted string choices, numeric bounds and undeclared fields. It produces deterministic text or JSON reports with value-free issue messages and automation-friendly exit codes. It does not execute n8n, call webhooks, inspect credentials, fetch remote data or implement the full JSON Schema specification.
/ Impact
Required and optional field checks
Seven supported JSON value types
String, array and numeric limits
Unknown-field allow or reject policy
Duplicate-key rejection
Value-free text and JSON reports
1 MB and 100-field input limits
Twelve standard-library tests
Python standard library
Argparse, JSON, pathlib and regular expressions provide a dependency-free offline command-line tool.
Declarative contracts
A deliberately small rule format covers common workflow boundaries without claiming full JSON Schema compatibility.
Unittest
Twelve tests cover valid data, required fields, unknown keys, types, bounds, arrays, duplicate keys and CLI exit behavior.