What Is DNS? Why Your Domain Change Is Not Live Yet
DNS turns the name people type into the address a server answers on. Here is how it works, which records you edit, and why a change can take a while to show up.
What is DNS? The Domain Name System is the lookup service that turns a name people can remember, like a website address, into the numeric address of the server that actually hosts it. Without it you would type a string of digits to visit any site. When you connect a custom domain to an app your AI tool built, DNS is the step where you tell the internet which server that name should point to.
MDN defines it as "a hierarchical and decentralized naming system for Internet-connected resources" that "maintains a list of domain names along with the resources, such as IP addresses, that are associated with them." The two words that matter for a builder are "list" and "associated". DNS is a list, and you are the one who edits your entry.
What happens when someone opens your site
MDN's walkthrough of what a domain name is describes the sequence in plain steps, and it is worth knowing because each step is a place a change can be stuck:
A person types your address into the browser.
The browser asks the computer whether it already knows the matching IP address, using a local DNS cache. If so, it goes straight to the server.
If not, the computer asks a DNS server, "whose job is precisely to tell your computer which IP address matches each registered domain name", as MDN puts it.
Now that the browser has the address, it can ask the web server for the page.
The whole lookup usually takes a fraction of a second. The detail that trips people up is step two. Answers are stored, or cached, at several points along the way, and that is the reason a change you made ten minutes ago may not be visible to everyone yet.
The records you will actually edit
A DNS "record" is one line in the list for your domain. Dozens of types exist, but pointing a domain at an AI-built app involves four. The descriptions below follow Cloudflare's DNS record reference.
Record | What it does | When you touch it | Symptom when wrong |
|---|---|---|---|
A | Maps a name to an IPv4 address (AAAA does the same for IPv6) | Pointing the bare domain at a host that gives you an address | Site does not load, or loads a different site |
CNAME | Maps a name to another name instead of an address | Pointing "www" or an app subdomain at your host's hostname | "Server not found" on that subdomain |
MX | Says which mail server receives email for the domain | Setting up business email | Email to your domain bounces or vanishes |
TXT | Holds a piece of text, often to prove you own the domain | Verifying ownership with a host or email provider | Host keeps saying the domain is "unverified" |
Two rules of thumb. First, your hosting provider will tell you exactly which values to enter, so the job is copying them carefully, not designing anything. Second, a CNAME points at a name, never at a number. If a tool asks you to put an IP address in a CNAME field, something has been mixed up.
Why changes take time
Every DNS answer carries a number called TTL, short for time to live. Cloudflare's reference describes it as controlling "how long DNS resolvers should cache a response before revalidating it." MDN says the same thing from the other side: each DNS server stores the information "for some time before it is automatically invalidated and then refreshed."
That is all "propagation" is. There is no wave travelling across the internet. Different resolvers simply hold the old answer until their stored copy expires, then fetch the new one. Practical consequences:
If you know a change is coming, lower the TTL a day ahead, make the change, then raise it again.
If your phone shows the new site and your laptop shows the old one, that is two caches expiring at different times, not a broken setup.
Check from a different network, such as mobile data, before concluding the change failed.
A worked example: pointing a domain at a new app
Say your AI-built app is hosted and the host gives you a target hostname. The usual steps are:
Open the DNS settings where you bought the domain, or the DNS provider you delegated to.
Add a CNAME for "www" pointing at the hostname your host gave you.
Add or edit the A record for the bare domain with the address your host gave you.
Add the TXT record the host asks for, to verify you own the domain.
Wait, then test from two networks.
The longer walkthrough, including what to do when the host refuses to verify, is in how to move an AI-built app to a custom domain.
Where AI tools go wrong with DNS
DNS is one of the few areas where a small mistake can take a whole business offline, so it deserves caution with agents.
An agent may "helpfully" replace the existing records instead of adding to them, which silently breaks email if the MX or TXT lines are lost. Export or screenshot your current records before any change.
Giving an agent permission to edit DNS is a bigger step than it looks, and is it safe to let an AI agent manage your DNS settings goes through the risks.
Email trouble after a domain change is often a missing TXT record. Why emails from your AI-built app go to spam covers the sender checks that use them.
If you want the surrounding picture of getting an app live, the pillar guide on how to build an app with AI links the rest of the steps.
Frequently asked questions
What is DNS in simple words?
It is the internet's phone book. You give it a name, it gives back the numeric address of the server that should answer. Your domain registrar or DNS provider holds the entries for your own domain.
How long does a DNS change take?
It depends on the TTL stored with the old record. Resolvers keep the old answer until that time runs out, so some visitors see the change quickly and others later. Lowering the TTL before a planned change shortens the wait.
What is the difference between an A record and a CNAME?
An A record points a name at an IPv4 address. A CNAME points a name at another name, and the lookup continues from there. Hosts that change addresses often prefer CNAMEs so you never have to update a number.
Do I need to understand DNS to use a custom domain?
Not deeply. You need to copy the values your host gives you into the right record types and then wait for caches to refresh. Understanding TTL and the four record types above covers most real situations.
Why does my domain work on my phone but not my laptop?
Each device and network keeps its own cached answers. One cache has refreshed and the other has not. Waiting, or switching networks, usually resolves it.
How did this land?
About the author
Senior Editor, AI & Product
Cecilia leads the Swarmz editorial desk. She has spent a decade turning complex AI and product topics into writing people actually finish, and she owns the blog's quality bar.
