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Assertions define what “healthy” means for your HTTP monitor. Each check evaluates all assertions and records a pass or fail result. A failed fail-severity assertion causes the check to fail; a failed warn-severity assertion records a DEGRADED hint without triggering a DOWN incident.
Severity levels Severity Behavior failCheck is marked as failed. Contributes to incident trigger rules. warnCheck passes but records a DEGRADED severity hint. Can trigger degraded incident rules.
Assertion types status_code Validate the HTTP response status code.
Field Type Required Description expectedstring Yes Expected status code (e.g., "200", "2xx") operatorstring Yes equals, contains, matches, range
assertions : - config : type : status_code expected : "200" operator : equals severity : fail
Use range to match a range of status codes:
assertions : - config : type : status_code expected : "200-299" operator : range severity : fail
response_time Fail when response latency exceeds a threshold.
Field Type Required Description thresholdMsinteger No Maximum acceptable response time in milliseconds
assertions : - config : type : response_time thresholdMs : 2000 severity : fail
response_time_warn Record a degraded hint when response time is elevated but not critical.
Field Type Required Description warnMsinteger No Warning threshold in milliseconds
assertions : - config : type : response_time_warn warnMs : 1000 severity : warn
Use response_time with fail severity for outage detection and response_time_warn with warn severity for early degradation alerts.
body_contains Check that the response body contains a specific substring.
Field Type Required Description substringstring Yes Text to search for in the response body
assertions : - config : type : body_contains substring : '"status":"ok"' severity : fail
json_path Extract a value from a JSON response using JSONPath and compare it.
Field Type Required Description pathstring Yes JSONPath expression (e.g., $.status) expectedstring Yes Expected value operatorstring Yes equals, contains, less_than, greater_than, matches, range
assertions : - config : type : json_path path : $.status expected : healthy operator : equals severity : fail
Validate a response header value.
Field Type Required Description headerNamestring Yes Response header name expectedstring Yes Expected value operatorstring Yes equals, contains, less_than, greater_than, matches, range
assertions : - config : type : header_value headerName : content-type expected : application/json operator : contains severity : fail
regex_body Match the response body against a regular expression.
Field Type Required Description patternstring Yes Regular expression pattern
assertions : - config : type : regex_body pattern : '"version":\s*"\d+\.\d+\.\d+"' severity : fail
ssl_expiry Alert before TLS certificates expire. Requires verifyTls: true (the default).
Field Type Required Description minDaysRemaininginteger No Minimum days until expiry (default depends on severity)
assertions : - config : type : ssl_expiry minDaysRemaining : 30 severity : warn - config : type : ssl_expiry minDaysRemaining : 7 severity : fail
response_size Limit the response body size.
Field Type Required Description maxBytesinteger No Maximum response size in bytes
assertions : - config : type : response_size maxBytes : 1048576 severity : warn
redirect_count Limit the number of redirects followed.
Field Type Required Description maxCountinteger No Maximum number of redirects
assertions : - config : type : redirect_count maxCount : 3 severity : warn
redirect_target Verify the final redirect destination URL.
Field Type Required Description expectedstring Yes Expected final URL operatorstring Yes equals, contains, matches
assertions : - config : type : redirect_target expected : https://www.example.com operator : equals severity : fail
Operators reference Operator Behavior Applies to equalsExact string or numeric match status_code, json_path, header_value, redirect_targetcontainsSubstring match status_code, json_path, header_value, redirect_targetless_thanNumeric less-than json_path, header_valuegreater_thanNumeric greater-than json_path, header_valuematchesRegex match status_code, json_path, header_value, redirect_targetrangeNumeric range (e.g., "200-299") status_code, json_path, header_value
Common patterns
Health check with status + latency
assertions : - config : type : status_code expected : "200" operator : equals severity : fail - config : type : response_time thresholdMs : 3000 severity : fail - config : type : response_time_warn warnMs : 1500 severity : warn
assertions : - config : type : status_code expected : "200" operator : equals severity : fail - config : type : json_path path : $.status expected : healthy operator : equals severity : fail - config : type : header_value headerName : content-type expected : application/json operator : contains severity : fail
assertions : - config : type : status_code expected : "200" operator : equals severity : fail - config : type : ssl_expiry minDaysRemaining : 30 severity : warn - config : type : ssl_expiry minDaysRemaining : 7 severity : fail
Next steps
HTTP configuration Headers, body, TLS, and auth fields.
SSL monitoring guide Certificate expiry monitoring patterns.
Incident policies How assertion failures trigger incidents.
Monitoring as Code Define assertions in YAML.
