How to set up a custom short domain

Step 1: decide on the hostname

You need to choose between a subdomain of a domain you already own, such as go.example.com, and the root of a dedicated short domain, such as exa.mp. Subdomains are simpler because they use a CNAME record and never collide with your website. Root domains need an A record or an ALIAS-style record, and the domain cannot also host a site on the same hostname. The subdomain vs dedicated domain entry covers the trade-off; if in doubt, use a subdomain.

Step 2: add the DNS record

In your shortener's domain settings, add the hostname you chose. The shortener will show you a target to point it at. Then open the DNS management page at the registrar or DNS host for the domain and create the record.

• Subdomain: create a CNAME record. Name is the subdomain label, for example go. Value is the target the shortener displayed. A CNAME says "this name is an alias for that name", so the shortener can move its servers later without you changing anything.
• Root domain: CNAME records are not allowed at the apex of a zone, so create an A record with the IP address the shortener provides, or use the ALIAS, ANAME or CNAME-flattening feature your DNS host offers. Cloudflare, Route 53 and most modern hosts support one of these.

Leave the TTL at the default. Do not add the record to both a CNAME and an A record for the same name; a hostname can have one or the other.

Step 3: wait for propagation

DNS changes are cached. Resolvers around the world keep the old answer for up to the previous record's TTL, and a brand-new record is usually visible within a few minutes. Forty-eight hours is the worst case, almost never the real one. You can check from the command line with dig go.example.com CNAME or an online DNS checker that queries several locations. When the response shows the shortener's target, you are ready to verify.

Step 4: verify and issue the certificate

Back in the shortener's domain settings, trigger verification. The shortener looks up your hostname, confirms it points at its infrastructure, and then requests a TLS certificate for it. ReSlug, Short.io, Dub and Cuttly do this automatically; the certificate is typically ready a minute or two after verification succeeds. Other vendors do not document their certificate flow on the pricing page, so check the help centre before relying on it.

If verification fails, the DNS record is wrong or has not propagated to the resolver the shortener uses. Wait ten minutes and retry before changing anything. The SSL entry explains what the certificate does and why you should not publish links until it is active.

Step 5: test and switch the default

Create one short link on the new domain and open it on a phone that is not on your office network, so you are testing from a fresh resolver. Confirm three things: the browser shows the padlock, the redirect lands on the right page, and the click shows up in analytics. Then set the custom domain as the default for new links in the shortener, so nothing gets created on the vendor's shared domain by accident.

Keep the DNS record in place for as long as any link on the domain exists. Deleting the record breaks every link at once.

Optional: what the root should do

If your short domain is a dedicated one, visitors will sometimes type the bare domain. Decide where that goes. Most shorteners let you set a root redirect to your main website. If yours does not, add a redirect rule at the DNS host or registrar so exa.mp sends people to example.com rather than an error page.