Compare a domain's records across major public resolvers to see whether a recent DNS change has taken effect.
DNS is cached at every step to keep the internet fast. Each record has a TTL (time to live) that tells resolvers how long to hold the answer before checking again. After you make a change, resolvers keep serving the old value until their cache expires, which is why a new record can appear in some places before others.
Want to inspect the records themselves? Use the DNS lookup tool, or learn how DNS works.
When you change a DNS record, resolvers around the world keep the old answer cached until it expires. Propagation is the period while that change spreads. It can take minutes to a couple of days depending on the record's TTL.
It queries the same record from several major public resolvers at once and compares the answers. If they all match, the change has likely propagated. If they differ, it's still spreading.
Usually a few minutes to a few hours, but it can take up to 48 hours. Lowering a record's TTL before you make a change makes future updates propagate faster.