Website (HTTP) monitors

What it checks

An HTTP monitor requests a URL from Mon's locations and checks the answer: that it arrives in time, that its status code is one you count as up, and - if you ask - that the page says what it should, ends up at the right address and has a valid certificate.

Adding one

Under Monitors, choose Add Monitor, then HTTP, and enter the URL. A URL without http:// or https:// gets https://. To add several sites at once, choose Add several at once and paste one URL per line.

The form's steps:

1. Target - the URL, and the advanced request options below.
2. Validation - what counts as up.
3. Monitoring - interval, timeout, maintenance windows and locations. See How checks work.
4. Alerts - who's told, and when. See Alerts and contacts.
5. Name - suggested from the URL.

The request

Under Advanced options:

• HTTP Method - HEAD by default, which fetches only the headers and is the lightest on your server. With a keyword set, Mon fetches the whole page with GET instead, since there's nothing to search in a HEAD.
• IP Protocol - Automatic, IPv4 or IPv6, to check one specifically.
• Body - for POST, PUT and PATCH: either raw content, with a content type of JSON (the default), XML or form-encoded, or form fields as names and values. A request with one of these methods and no body is counted as a failure.
• Custom Headers - extra headers to send, such as an API key. Paid plans.
• Username and Password - for pages behind HTTP authentication. The password is stored and never shown again; choose Remove Password to clear it. Paid plans.
• User Agent - what the request identifies itself as. Left blank, it's Mon Bot v1.
• Allow JavaScript Redirects and Allow Meta Redirects - see below.

What counts as up

• Up Status Codes - the codes that count as up. By default, the 2xx and 3xx codes: 200-208, 226 and 300-308. Changing them needs a paid plan.
• Keyword - a word or phrase to look for on the page. With Keyword must exist on (the default), the monitor is down if it's missing; turn it off to be told when it appears instead - an error message, say. Case Sensitive matches capitals exactly. Mon searches the text a visitor reads; Raw Keyword Check searches the page's HTML source instead.
• Expected URL - the address the request should end up at after redirects. Choose which parts must match: the sub-domain, the path, and the query and fragment.

Redirects

Mon follows 301, 302, 303, 307 and 308 redirects automatically, up to 10 of them, and stops a loop. Redirects made by JavaScript or by a <meta> refresh tag are followed only when Allow JavaScript Redirects or Allow Meta Redirects is on.

The certificate

With Monitor SSL on, the check also requires a valid certificate: a certificate that has expired, is issued for another name, or doesn't chain to a trusted root makes the monitor go down. The reminders beneath it - 30, 7 and 1 day on to start with, 15 if you add it - tell you before the certificate expires - a certificate that's only close to expiry doesn't take the site down.

Certificate checking is included on every plan. For certificates on other ports - mail, admin panels - use an SSL monitor.

Why a check fails

Each failed check records its reason:

Reason	What happened
Status code	The page answered with a code not in your up list - 503, say
Timeout	No answer within the timeout
Connection refused, reset or aborted	The server wouldn't connect, or dropped the connection
DNS resolution failed	The host name couldn't be looked up
Keyword	The keyword was missing - or present, if you're watching for it to appear
URL mismatch	The page ended up somewhere other than the expected URL
Redirect loop, too many redirects	The redirects went round in circles, or past 10
SSL	With Monitor SSL on, the certificate wasn't valid

On the Free plan

Custom headers, custom up status codes and HTTP authentication need a paid plan, and checks run at most every 5 minutes. Everything else, certificate checking included, is on every plan.