JSON Path Assertions: Validate Nested API Responses

What is a JSON Path assertion?

A JSON Path assertion is a rule that points to a specific field inside a JSON response body and validates its value. Instead of scanning the entire body for a pattern (regex), you target exactly the field you care about.

// Response:
{
  "status": "ok",
  "data": {
    "user_id": 42,
    "balance": 1500,
    "plan": "pro"
  },
  "error": null
}

// Assertions:
$.status          ==       "ok"       ✓ passes
$.data.balance    >=       100        ✓ passes
$.error           is_null             ✓ passes
$.data.plan       ==       "free"     ✗ fails → alert fires

Which Operators Does CheckAPI Support for JSON Path Assertions?

CheckAPI supports 11 operators for JSON Path assertions:

What Are Real-World JSON Path Assertion Examples?

Health check endpoint

// GET /health
{
  "status": "ok",
  "db": "connected",
  "cache": "connected",
  "version": "2.4.1"
}

// Assertions:
$.status    ==           "ok"
$.db        ==           "connected"
$.cache     ==           "connected"
$.version   is_not_null

Payment API

// POST /payments/process
{
  "success": true,
  "transaction_id": "txn_abc123",
  "amount_charged": 4999,
  "error": null
}

// Assertions:
$.success           ==         true
$.transaction_id    exists
$.amount_charged    >          0
$.error             is_null

List endpoint (data must not be empty)

// GET /api/products
{
  "data": [...],
  "total": 142,
  "page": 1
}

// Assertions:
$.total     >     0
$.data      is_not_null

Should You Use AND or OR Logic for JSON Path Assertions?

By default, all assertions are evaluated with AND logic — every assertion must pass for the check to be green. You can switch individual assertions to OR in the Assertions tab, which means the check passes if at least one assertion is true.

How Many JSON Path Assertions Can You Set Per Monitor?

CheckAPI supports up to 10 JSON Path assertions per monitor. This is enough to comprehensively validate the critical fields of any API response in a single check — no code required.

Can You Combine JSON Path Assertions with Regex?

JSON Path and Regex aren't mutually exclusive. A common pattern is to use Regex for a quick top-level sanity check (e.g. error field is null) and JSON Path for precise field-level validation (e.g. balance is positive, user_id exists). Both run on every check.