Assertions define the conditions that a synthetic check must satisfy. If any assertion fails, the check is marked as Critical or Degraded, depending on the severity you configure. This allows you to enforce correctness (status codes, response data) as well as performance (latency, timing) requirements.

Available Assertions

Validate Status Codes

Validate the HTTP response status code.

Example: = 200 → the request must return 200 OK or the check will fail.

Set Timing Thresholds

You can add performance thresholds for different stages of the HTTP request lifecycle:

Response – total response time
Request – time to send the request
SSL – time for the TLS handshake
Connection – TCP connection establishment time
DNS – DNS resolution time
Total – end-to-end time

Example: Response < 5000 ms (Critical), Response < 2000 ms (Degraded)

This lets you distinguish between slow and failing services.

Match Error Types

Define which error types should cause a failure:

DNS – failures resolving the hostname
Connection – TCP connection could not be established
SSL – TLS handshake failure
Timeout – request exceeded maximum duration
Unknown – uncategorized errors

Verify SSL Certificate Validity

Enforce that the target server's TLS certificate remains valid for a minimum number of days.

Example: SSL certificate validity > 30 days → ensures certificates are rotated in time.

Check Response Headers

Validate the presence or value of a specific response header.

Example: x-auth-token = Bearer example-token

Assert JSON Body Content

Validate the structure or values in a JSON response using JSONPath. Use JSON Body assertions to validate fields inside a JSON response with JSONPath. This ensures your checks go beyond status codes and verify the actual API response content.

Examples:

JSONPath Expression	Passes For
`$.status = 200`	`{ "status": 200 }`
`$.user.name = "Alice"`	`{ "user": { "name": "Alice" } }`
`$.items[0].id = 123`	`{ "items": [ { "id": 123 } ] }`
`$.features.beta = true`	`{ "features": { "beta": true } }`

Match Text Body

Check if the plain-text body matches a value.

Example: Response body = "OK"

Configure Severity Levels

Critical – indicates the check has failed completely (e.g., wrong status code, timeout, certificate expired).
Degraded – indicates the check succeeded but with performance or quality below expectations (e.g., slower than target latency).

Define Synthetic Check Success Criteria