Look for a reassuring phrase

Choose a literal phrase

Open Response text in the monitor editor and choose Must contain or Must not contain. Enter between 1 and 200 characters. This is a literal phrase match, not a regular expression.

Matching ignores letter case unless you enable Match letter case. HTML is checked as response source, not as a rendered page; text inserted later by browser JavaScript will not be available to the check.

1. Choose Must contain.
2. Enter All systems ready.
3. Leave Match letter case off if capitalization can vary.
4. Save and run a check.

Catch an application error behind a successful status

If your endpoint returns HTTP 200 even when it displays an error, a Must not contain rule can check for a known error phrase. A response containing that phrase fails the rule.

Choose text that reliably describes health. A phrase in a comment, script or unrelated section of the source can also match.

When the owl cannot verify the text

The checker reads up to 64 KiB of supported UTF-8 response text within the check timeout. Unsupported content or undecodable text reports an issue.

For HTTP checks, a phrase found in the bounded read is evaluated normally. If the HTTP response is truncated and the phrase has not been found, the rule cannot be verified and reports an issue—even for Must not contain. WebSocket checks instead require the first complete text message to fit within 64 KiB; oversized or binary messages fail. We do not skip greetings or inspect later messages. Use a small, dedicated health response for predictable results.