Assertions reference

Assertions verify that response data is correct. If any assertion fails, the check is marked as DOWN.

Assertion types

Status code

Choose Status code → Is one of and select one or more acceptable HTTP response codes. For example, select 401 Unauthorized when an endpoint should reject unauthenticated requests.

Any selected code is accepted. All other assertions and text searches must also pass. Without a status code assertion, any 2xx response is accepted. Network errors, TLS failures and timeouts always fail.

Field	Value
Property	Not used
Comparison	Is one of
Expected value	One or more unique codes from 100 through 599

Each HTTP check supports one status code assertion. Redirect settings determine whether the assertion checks the redirect response or its destination. History retains the actual response code, including accepted non-2xx responses.

For the API, use:

{
  "type": "STATUS_CODE",
  "property": "",
  "comparison": "IS_ONE_OF",
  "expected": [200, 204]
}

JSON body

Assert on values in JSON responses using JSONPath.

Field	Description
Property	JSONPath expression (e.g., $.data.user.name)
Expected value	Value to match

Use the JSONPath online sandbox to test expressions.

Text body

Assert on text content anywhere in the response body.

Field	Description
Property	Not used; text body assertions check the whole response body
Expected value	Text to match (for comparisons such as Contains or Equals)

Response headers

Assert on HTTP response headers.

Field	Description
Property	Header name (e.g., Content-Type)
Expected value	Expected header value

HTML body

Assert on HTML elements using CSS selectors.

Field	Description
Property	CSS selector (e.g., meta[name="viewport"])
Expected value	Expected element content

Notes:

• Commented-out elements (<!-- ... -->) are not found
• Supports all CSS selectors
• HTML assertions check the selected element's text content, except meta tags where they check the content attribute
• Empty elements like <link> can be checked for existence with Not null, but Not empty will fail because they have no text content
• To check a <link> attribute such as href, include it in the selector, for example link[rel="canonical"][href="https://example.com/page"] with Not null

Common CSS selector patterns:

Selector	Matches
meta[name="viewport"]	Exact attribute match
link[rel="canonical"]	Canonical link tag exists
link[rel="canonical"][href="https://example.com/page"]	Canonical link with exact URL exists
script[src*="analytics"]	Attribute contains substring
[property^="og:"]	Attribute starts with
[href$=".pdf"]	Attribute ends with
.cookie-banner	Class name
#main-content	ID

Comparisons

Comparison	Description
Equals	Exact match
Not equals	Does not match
Greater than	Numeric comparison
Less than	Numeric comparison
Null	Value is null
Not null	Value exists
Empty	Value is empty string
Not empty	Value has content
Contains	Substring match
Not contains	Substring not present
True	Boolean true
False	Boolean false