n8n-nodes-input-validation

Custom n8n community node for validating incoming API and webhook data — parameters, body fields, and headers — and routing the result to Valid or Invalid outputs.

When you use n8n as an API gateway, every endpoint needs to check that required fields exist and match the expected format. Today that usually means chaining Webhook → IF → SET → Respond to Webhook just to return a 400 with a readable error. This package replaces that pattern with a single node.

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What does it do?

The Input Validation node reads fields from the incoming item (using dot-notation paths like body.email or query.page), evaluates your rules, and:

• Valid — passes the original input through unchanged (continue your workflow)
• Invalid — outputs a ready-made error object for Respond to Webhook (status code, plain-text error, and structured errors array)

No credentials required. Works with any trigger that outputs JSON (typically Webhook).

Before vs After

Without this node:

Webhook → IF (field checks) → SET (build error JSON) → Respond to Webhook
         → IF (else branch)  → your business logic

With this node:

Webhook → Input Validation ─ Valid   → your business logic → Respond 200
                          └ Invalid → Respond to Webhook ({{ $json }})

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Node in this Package

Node	Type	Description
Input Validation	Transform	Validate fields with rule groups; route to Valid or Invalid

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Installation

Community Nodes (Recommended)

1. Go to Settings → Community Nodes in your n8n instance
2. Click Install a community node
3. Enter n8n-nodes-input-validation
4. Click Install and restart n8n if prompted

Manual Installation

cd ~/.n8n/custom   # or your N8N_CUSTOM_EXTENSIONS path
npm install n8n-nodes-input-validation
# Restart n8n

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Input Validation Node

Configuration

Setting	Description
Combine Groups	AND = every group must pass · OR = at least one group must pass
Rule Groups	One or more groups of conditions (see below)
Combine Conditions (per group)	AND = all conditions in the group · OR = at least one condition
Field	Dot-notation path on the incoming JSON, e.g. body.email, query.page, headers.x-api-key
Operation	See Operators
Value	Comparison value (not used for empty/boolean-only operations)
Default Value	When the field is missing: skip this condition, and add the default to the Valid output JSON
Error Message	Optional custom text when this condition fails

Options

Option	Default	Description
Ignore Case	true	Case-insensitive string comparisons
Error Status Code	400	HTTP code in the Invalid output (statusCode)
Include Original Input	false	Adds original with the full input JSON on Invalid
Error Message	Validation failed	Summary text in the Invalid output (message)

How it works

1. A request hits your workflow (e.g. via Webhook)
2. The node reads each configured Field from the item JSON
3. Conditions are evaluated inside each Rule Group, then groups are combined with Combine Groups
4. All rules pass → item goes to the Valid output (unchanged)
5. Any rule fails → item goes to the Invalid output with a structured error payload

Operators

Operation	Value	Description
Is Empty	—	null, undefined, "", or empty array
Is Not Empty	—	Field must have a value
Contains	Yes	String contains the value
Does Not Contain	Yes	String does not contain the value
Equals	Yes	String equality (respects Ignore Case)
Does Not Equal	Yes	String inequality
Greater Than	Yes	Numeric comparison (body.age > 18)
Less Than	Yes	Numeric comparison
Is True	—	Value must be true (boolean, or true / 1 as string)
Is False	—	Value must be false (boolean, or false / 0 as string)
Is Boolean	—	Value must be a valid boolean (true or false)

Accepts native booleans and common API string forms: true, false, 1, 0 (case-insensitive).

Rule groups example

Validate that either (email AND age) or (premium OR enterprise plan):

Combine Groups	OR
Group 1 — Combine Conditions: AND	body.email · Is Not Empty
	body.age · Greater Than · 18
Group 2 — Combine Conditions: OR	query.type · Equals · premium
	query.type · Equals · enterprise

Logic: (email ∧ age>18) ∨ (type=premium ∨ type=enterprise)

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Invalid Output

When validation fails, the Invalid branch receives:

{
  "valid": false,
  "statusCode": 400,
  "message": "Validation failed",
  "error": "body.email must not be empty; body.age must be greater than 18",
  "errors": [
    {
      "field": "body.email",
      "operation": "isNotEmpty",
      "message": "body.email must not be empty",
      "received": null
    },
    {
      "field": "body.age",
      "operation": "greaterThan",
      "message": "body.age must be greater than 18",
      "received": "12"
    }
  ]
}

Field	Use
statusCode	Set Respond to Webhook → Response Code to {{ $json.statusCode }}
error	Plain-text body — all failures joined with ;
errors	Full list for logging or JSON API responses
message	Short summary line
original	Present only if Include Original Input is enabled

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Examples

Example: Missing field with default (skip + inject)

Field	Operation	Default Value
Test	Is Empty	false

Input: { "ClientName": "Moses" } — no Test field.

• The Is Empty condition is skipped (field does not exist)
• Valid output: { "ClientName": "Moses", "Test": false }

If the client sends Test, the condition runs normally (Is Empty must pass).

Example: POST API with required body fields

Workflow:

Webhook (POST /api/orders)
  → Input Validation
      Valid   → Create Order → Respond to Webhook (200)
      Invalid → Respond to Webhook
                  Response Code: {{ $json.statusCode }}
                  Response Body: {{ $json }}

Rules (single group, AND):

Field	Operation	Value
body.customer_id	Is Not Empty
body.amount	Greater Than	0
body.currency	Equals	USD

Invalid response (what the client sees if body.amount is missing):

{
  "valid": false,
  "statusCode": 400,
  "message": "Validation failed",
  "error": "body.amount must not be empty",
  "errors": [ ... ]
}

Example: Simple text error response

Connect Invalid → Respond to Webhook:

• Response Code: {{ $json.statusCode }}
• Response Body: {{ $json.error }}

Client receives: body.email must not be empty; body.age must be greater than 18

Example: calling the webhook

curl -X POST https://your-n8n.com/webhook/orders \
  -H "Content-Type: application/json" \
  -d '{"customer_id": "c_1", "amount": 99, "currency": "USD"}'

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License

MIT