Website monitoring glossary

Plain definitions of the terms behind website monitoring, each with what it means for a client site and a link to the guide that goes deeper.

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AvailabilityAvailability is the share of a period a service worked. The formula, how it converts to minutes of downtime, and why a chain of services is less available.

Canonical URLThe canonical URL is the address a search engine treats as the main version of a page that exists at several URLs. How rel=canonical, redirects and sitemaps signal it.
Care planA website care plan is a recurring service in which an agency monitors, updates, backs up and reports on a client site for a monthly fee. What belongs in one.
Certificate authorityA certificate authority is an organisation browsers trust to issue TLS certificates after checking that the requester controls the domain. How validation and renewal work.
Check intervalThe check interval is the time between two uptime checks. How it sets the detection delay, the number of checks and how it interacts with confirmation.
CNAMEA CNAME record makes one name an alias of another. Why a name with a CNAME cannot hold other records, which blocks it from the root of a domain.
CrawlingCrawling is how a search engine fetches pages by following links and sitemaps. What affects it, why robots.txt and server errors change crawl rate and what crawl budget means.
Cron jobA cron job is a task scheduled to run at set times on a server. Why it fails silently, how WP-Cron differs from system cron and how to monitor it.

DKIMDKIM adds a cryptographic signature to outgoing email, verified with a public key in DNS. Where the key lives and what happens when the selector record is removed.
DMARCDMARC is a DNS policy that tells receivers what to do with email that fails SPF and DKIM alignment: nothing, quarantine or reject. Why strict policies amplify DNS mistakes.
DNS recordA DNS record is one entry in a domain’s zone that maps a name to data such as an address, a mail server or a text value. The common types and what breaks when one changes.
Domain expiryDomain expiry is the date a domain registration ends unless renewed. What happens in the days after it, why reminders fail and how to monitor the date.

False positiveA false positive is an alert saying a site is down when it was reachable. Usual causes: the monitor’s network, DNS, firewalls and timeouts, and how to cut them.

Heartbeat monitoringHeartbeat monitoring waits for a scheduled job to report in and alerts when the signal is missing. How the period and grace time work and what it is good for.
HSTSHSTS is a response header that tells browsers to use only HTTPS for a site. What max-age and includeSubDomains do, and why it turns an expired certificate into a hard failure.
HTTP status codeAn HTTP status code is the three-digit number that opens a server response and says how the request went: 2xx success, 3xx redirect, 4xx client error, 5xx server error.

IncidentAn incident is a period in which a monitored site is confirmed to be failing, from first confirmation to recovery. What an incident record should hold.
IndexingIndexing is how a search engine stores a page it has crawled so it can be returned for queries. What decides whether a page is indexed and why crawled does not mean indexed.

MX recordAn MX record lists the mail servers for a domain with priorities. What happens to email when it is missing or points to the wrong provider.

NameserverA nameserver is the server that holds a domain’s DNS records and answers queries for them. Why moving nameservers moves the whole zone and what to copy first.
NoindexNoindex is a robots directive, set in a meta tag or header, that tells search engines not to keep a page in their index. How Google reads it and its common failure.

RDAPRDAP is the standard, JSON-based way to look up domain registration data, including the expiry date. How it differs from WHOIS and what its events list contains.
RedirectA redirect is an HTTP response that sends a visitor or crawler to another URL. The permanent and temporary status codes and how Google treats each.
Redirect chainA redirect chain is a sequence of redirects between the first URL and the final page. How many hops Google follows and why to collapse chains to a single hop.
Regional issueA regional issue is when one monitoring region sees a failure and another does not. Why it is not the same as an outage and why it still deserves a look.
RegistrarA registrar is the company through which a domain is bought and renewed. What it controls, what the registry does and why the registrar account matters for client sites.
robots.txtrobots.txt is a text file at the top of a site that tells crawlers which URLs they may fetch. It manages crawling, is not security and cannot reliably hide pages.

SitemapAn XML sitemap lists the URLs a site wants search engines to know about. Google’s size limits, how lastmod is used and what belongs in the file.
SLAAn SLA is a written commitment on service levels such as availability and response time, how they are measured, what follows a miss, and the formulas behind it.
Soft 404A soft 404 is a page that looks like an error or is empty but returns a success status. How Google reports it and how to catch error pages that answer 200.
SPFSPF is a DNS record listing the servers allowed to send email for a domain. The one-record rule, the ten-lookup limit and the mistakes that make mail fail.
Status pageA status page is a public page that shows whether a service works and lists incidents. What it should show, how to word updates and why blips stay off it.

TLS certificateA TLS certificate proves that a website holds the name in the address bar and enables HTTPS. What it contains, how long it lasts and what happens when it expires.
TTLTTL is the number of seconds a DNS answer may be cached. How it makes DNS changes spread slowly, how to lower it before a change and why it is a maximum, not a promise.

Uptime monitoringUptime monitoring requests a website from outside at intervals and alerts when it fails to answer. What it measures, what it misses and how it is confirmed.

WHOISWHOIS is the older text-based service for looking up who registered a domain and when it expires. Why its format varies and why RDAP is replacing it.

X-Robots-TagX-Robots-Tag is an HTTP response header that carries robots directives such as noindex, for pages and for files like PDFs. Why it is easy to miss in the page source.

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