How to check if a website is down
A URL fails in one browser and you need an outside check from Cloudflare. Up means 2xx or 3xx. Down means a timeout, network error, or 5xx.
Read guide
Index and archive
Engineering guides and tool documentation
How-to guides for the PageUtil tools: what each check does, how to read the result, and which tool to open next.
80 guides
How to tell an outage from a 404
Someone says the site is down because a page will not load. 404 and 410 mean that URL is missing, not that the server is dead.
Read guide
How to read a slow response time
The site loads, but feels broken. The millisecond figure is time-to-response from Cloudflare, not full page load.
Read guide
How to see the final URL after a check
You pasted one address and the status belongs to another. Final URL is the last request. If it is a different host, you measured that host.
Read guide
How to check a site that blocks Cloudflare
The check fails, but the site works in your browser. A block, challenge, or empty failure against Cloudflare is inconclusive, not proof of an outage.
Read guide
How to look up what an HTTP status code means
A log or a check returned a number and you need the class. 1xx informational, 2xx success, 3xx redirect, 4xx client, 5xx server.
Read guide
How to tell a 301 from a 302
A move might be permanent or temporary, and caches will treat them differently. 301 and 308 are permanent. 302 and 307 are temporary.
Read guide
How to read the response headers for a URL
You need server, cache, cookie, or security-header evidence without the body. Status and final URL first. Then the header list.
Read guide
How to trace a redirect chain
A short link, http URL, or renamed page does not land where you expect. Each hop has a status, a URL, and a Location.
Read guide
How to spot a redirect loop
The browser says too many redirects. A repeated URL in the hop list, or a stopped reason of loop, is the loop.
Read guide
How to check whether a public port answers
You need to know if one public TCP port accepts a connection from Cloudflare. Reachable means connect() succeeded.
Read guide
How to read a port-check timeout
The result says timed out and someone wants to call the port closed. Timeout means no completed handshake from Cloudflare in time.
Read guide
How to see if HTTPS answers before you trust the certificate
The padlock is missing and you do not know if the port, the certificate, or the redirect is at fault. Down-check on https:// tells you the URL responded.
Read guide
How to confirm a site is up but unusable
Monitoring says up, users say broken. 200 with a tiny body is still up. 401/403 is up and refused. A redirect to an error host is up.
Read guide
How to look up a domain's A record
You need the IPv4 address the public DNS returns. NOERROR with answers means the name has A data. NXDOMAIN means the name does not exist.
Read guide
How to check whether a domain has IPv6
A v6-only network fails and you need to know if the name publishes AAAA. One or more AAAA answers means v6 is published.
Read guide
How to find the mail servers for a domain
Mail to the domain bounces or lands in the wrong system. MX answers are priority plus host. Lower priority number is preferred.
Read guide
How to read SPF and verification TXT records
A vendor asked you to prove a TXT record, or mail is failing SPF. SPF is the record that starts with v=spf1. TXT data is text.
Read guide
How to find a domain's nameservers
DNS edits are not showing up and you may be editing the wrong provider. NS answers are the servers publishing the zone.
Read guide
How to follow a CNAME to the real host
A www name or a SaaS hostname does not show an IP. CNAME data is the target name, not an IP. You still need A or AAAA on that target.
Read guide
How to read DNS TTL before you change records
You are about to cut over and want to know how long the old answer can stick. TTL is in seconds. 300 is five minutes. 86400 is a day.
Read guide
How to check who registered a domain
You need the registrar and the delegation, not a phone book. Privacy redaction is normal; missing contact fields are not a failed lookup.
Read guide
How to see when a domain expires
A renewal date is unknown. Expiry is the RDAP date. Updated is not expiry. Auto-renew can move expiry without a site change.
Read guide
How to read a domain status from RDAP
The domain looks registered but does not resolve. ok or active is normal. clientHold and serverHold stop DNS. clientTransferProhibited only locks transfers.
Read guide
How to check an SSL certificate's expiry date
You want days left before browsers reject the certificate. Days left under 14 is urgent. Under 30 is the usual renewal window.
Read guide
How to read the certificate issuer
You expect Let's Encrypt, a company CA, or Cloudflare, and need to see who actually signed. Issuer is the signing certificate's subject, not the site brand.
Read guide
How to investigate mail that never arrives
A form or a teammate says mail to a domain fails. Syntax fail means the address is malformed. MX missing or pointing at . means no mail host.
Read guide
How to prepare a domain before it expires
A domain you do not control day to day might lapse. RDAP expiry is the renewal deadline. Certificate days-left is independent.
Read guide
How to find your public IP address
A firewall, allow-list, or log needs the address the internet sees. The address is the one Cloudflare saw. It is not a LAN address like 192.168.x.x.
Read guide
How to tell whether you are on IPv4 or IPv6
A service behaves differently by protocol. Four decimal groups is IPv4. Groups with colons is IPv6. The page reports the family of the connecting address only.
Read guide
How to read your approximate location from your IP
You want a rough country, city, and network for this connection. Country is usually right. City can be the provider's location, not your street.
Read guide
How to see which network you are on
You need the ASN or ISP name for an allow-list note. ASN is the network number. Organisation may be a backbone, a VPN, or a mobile carrier.
Read guide
How to parse a browser user-agent string
A log line or a support paste needs browser, version, and OS. Browser and version come from tokens. The raw string is the source of truth.
Read guide
How to read a support ticket's client
It works for me, and you have a pasted user-agent plus the visitor on the phone. Parser output is the ticket. IP tools are the person on the phone.
Read guide
How to calculate an IPv4 subnet from CIDR
You have 203.0.113.10/26 and need the range. Network is the first address. Broadcast is the last. Usable addresses sit inside those two.
Read guide
How to size a subnet for a new network
You need N usable addresses and a prefix that covers them. Usable count must be at least N. A /24 has 254 usable. A /30 has 2.
Read guide
How to convert a Unix timestamp to a date
A log has 1710000000 or 1710000000000 and you need a wall time. Ten digits is seconds. Thirteen digits is milliseconds.
Read guide
How to turn a date into epoch seconds
An API wants a number and you have a calendar time. Use the seconds field unless the API docs say milliseconds. UTC is the value to send.
Read guide
How to tell seconds from milliseconds in a timestamp
A chart or a token expiry looks a thousand times off. Current epoch seconds is about 10 digits. Current milliseconds is about 13.
Read guide
How to check the current Unix time
You need a reference now while reading logs. Seconds, milliseconds, and ISO are the same instant. The page ticks. It is not a timezone database.
Read guide
How to read a cron expression in plain English
A five-field schedule is opaque. The English line is the schedule. The fields are minute, hour, day of month, month, and day of week.
Read guide
How to convert a time between time zones
A meeting or a log time needs to be read in another zone. The converted time is the same instant. The date can roll over. Trust the zone name.
Read guide
How to count down to a date
You want days, hours, minutes, and seconds until a local datetime. The split is remaining time, not a date difference in calendar units.
Read guide
How to work out days between two dates
A deadline needs a day count, not a countdown widget. Days is the interval. Weeks is days divided. The weekday note is context, not a business-day SLA.
Read guide
How to calculate age from a birth date
A form needs completed years, or you want years, months, and days. Years are completed years. Months and days are the remainder, not total months lived.
Read guide
How to schedule a job and state the next window
A crontab is about to be installed and the team is in another zone. Read the English schedule first, then convert the clock time to the reader's zone.
Read guide
How to generate a UUID
You need an id for a row, a request, or a filename. Version 4 means random, not time-ordered and not a hash of the content.
Read guide
How to generate a password that stays in the browser
You need a random password and do not want it sent anywhere. The string is the password. It is not stored and not strength-scored on this page.
Read guide
How to score a password's strength
A password exists and you want a local score before you use it. The score is a heuristic from length, classes, and common patterns. It is not a breach check.
Read guide
How to encode text as Base64
A header, a basic-auth toy, or a data URL needs Base64. Output is ASCII. Padding with equals is normal. Base64 is not encryption.
Read guide
How to decode a Base64 string
A log or a JWT segment looks like gibberish and might be Base64. Readable text means it was text. You still do not have a verified token.
Read guide
How to URL-encode a query string
A parameter contains spaces, &, or non-ASCII, and the request breaks. Encode a component, not a whole URL, or you will escape ://.
Read guide
How to decode a percent-encoded URL
A link is full of % sequences and you need the human value. Decoding once is usually enough. A result that still contains %26 was double-encoded.
Read guide
How to escape HTML before you display user text
Text might contain <, >, or & and will be inserted into HTML. Escaping is safe in element text. It is not a sanitiser for a whole HTML document.
Read guide
How to hash a string with SHA-256
You need a fingerprint to compare two values without storing the original. The hex digest is 64 characters. The same input always gives the same digest.
Read guide
How to decode a JWT header and payload
You have a bearer token and need the claims. The header names the algorithm and the payload is JSON. The signature is not checked.
Read guide
How to read the expiry claim in a JWT
A user is logged out and the token might be expired. exp is seconds since the epoch, UTC. If now is past exp, the claim says the token is expired.
Read guide
How to tell that a decoded JWT was not verified
Someone wants to treat a decoded role claim as authorisation. A successful decode is valid Base64url JSON. It does not mean the signature matched.
Read guide
How to format and validate JSON
A payload is one line, or a client says it is JSON and the parser disagrees. Formatted output means it parsed. The error line is the first break.
Read guide
How to minify JSON
A pretty payload is too large for a query or a snippet. Minified means whitespace removed and the same values. It is still not encrypted.
Read guide
How to format XML and read a parse error
A feed or a config will not parse. Formatted output means well-formed. The error is the first break: an unclosed tag, a bare ampersand, or a mismatched close.
Read guide
How to test a regular expression
A pattern should extract or accept a sample and you need to see the match. Matches are what JavaScript found. No match is a real result.
Read guide
How to compare two texts line by line
A config, a list, or a paragraph changed and you need the lines. Added, removed, and unchanged are by line. A reorder looks like a delete plus an add.
Read guide
How to count words and characters
A meta description, a title, or a post has a limit. Words are whitespace-separated. Keep titles near 60 characters and descriptions near 150.
Read guide
How to convert text case
A heading, a constant, or a sentence needs a different case. Upper and lower are mechanical. Title case capitalises small words. It will not fix names.
Read guide
How to turn a title into a URL slug
A page title needs a path segment. The slug is lowercase, with hyphens, and no leading or trailing hyphen. It is not checked for uniqueness on your site.
Read guide
How to generate lorem ipsum placeholder copy
A layout needs text that is not real content. Paragraphs are dummy Latin. Do not publish them. Word count is approximate to what you asked.
Read guide
How to remove duplicate lines
A paste of emails, hosts, or ids has repeats. The first occurrence is kept. Later copies are dropped. Comparison is the whole line.
Read guide
How to sort lines alphabetically
A list is hard to scan or you want a stable order before a diff. Sort is A to Z or Z to A. By character code, 10 can sort before 2.
Read guide
How to find and replace in pasted text
A repeated string in a paste needs swapping, without a full editor. The output is the paste with replacements. The count shows if the find was too narrow.
Read guide
How to check whether an email address is valid syntax
A form rejects an address, or you are cleaning a list. Valid means a plausible shape. It does not mean the mailbox exists, accepts mail, or is free of typos.
Read guide
How to make a QR code for a URL
A print or a slide needs a scannable link. The PNG encodes exactly the text you entered. A missing https still encodes. The page does not host the URL.
Read guide
How to make a Code 128 barcode
A label needs a Code 128 of an id or SKU. The image is that string. It is not a product lookup. A rejected character is a page error.
Read guide
How to convert a hex colour to RGB
A design tool speaks hex and a stylesheet wants RGB or HSL. #RRGGBB maps to three channels from 0 to 255. HSL is the same colour.
Read guide
How to check colour contrast for WCAG
Text on a background may fail accessibility. AA for normal text is 4.5 to 1. A pass for large text is not a pass for body text.
Read guide
How to make a letter favicon
A project needs a temporary icon. The PNG is a letter on a square at 32 or 180. It is not an ico set and not a maskable icon pack.
Read guide
How to generate Open Graph tags
A share card needs title, description, URL, and image tags. The snippet does not upload the image or prove the URL returns 200.
Read guide
How to write a robots.txt
You need allow, disallow, and a sitemap line. Disallow blocks crawlers that honour it. It is not access control. A sitemap line does not create the sitemap.
Read guide
How to write an Apache redirect rule
One path should move, permanently or not. The snippet is one rule, 301 or 302, from a path to a URL. It does not read your existing htaccess.
Read guide
How to look up a file's MIME type
A download opens as text, or a header needs a type. The type is the usual mapping for that extension. Unknown means the table has no entry.
Read guide