Is this domain available?

Check at the registry level whether a domain name is registered. Works for every TLD with RDAP, with a WHOIS fallback for the rest.

Try . Free, no account needed.

Need this at scale?

The same lookup is one API call at 1 credit / request (one credit is $0.0003 to $0.001 depending on volume), with failed requests free.

cURL

curl "https://api.gridlode.com/v1/domain/availability?domain=gridlode-labs.com" \
  -H "Authorization: Bearer $GRIDLODE_KEY"

Is 'available' a guarantee I can buy it?

It means the registry has no registration for the name. Premium or reserved names can still be unavailable or priced differently at registrars.