Start with the chip number, not the company name
You cannot trace a registry without the number, so find that first. Look through the paperwork that came with your dog: vet invoices and vaccination certificates often print it, adoption and breeder documents usually list it, and many clinics hand over a small card or sticker sheet when the chip goes in. If nothing in the folder carries it, book a quick scan. Any vet clinic, shelter, or rescue can pass a scanner over your dog's shoulders in seconds and read the number aloud, and there is no charge for that check at most clinics. Write the digits down exactly, in order, and photograph the scan result or paperwork so a smudged digit does not send you to the wrong registry later.
Run the number through a universal lookup
Microchip registries each keep their own database, but universal lookup tools search across the major registries at once. Type the full number in carefully, with no spaces added or digits dropped, and the result will name the company that holds the registration for that chip, along with its phone number or website. If the lookup returns more than one possible registry, which can happen with older chips, contact each one in turn and ask whether your dog's number is live on its system. The registry that matters is the one holding your name and phone number against that number, not simply the brand that manufactured the chip, and those two are often different companies.
Confirm what the registry actually holds
Finding the company is only half the job, because a registration is only useful when the details behind it are right. Ask the registry to read back the contact name, phone numbers, and address attached to your dog's chip, and correct anything left over from a previous owner, an old home, or the shelter that implanted it. Owners who adopted often discover the chip still points to the rescue, and owners who moved may find a landline that no longer exists. If the registry shows no registration at all, the chip was implanted but never enrolled, and you can register it yourself with that company or another registry the lookup suggests, using the number you already have.
Keep the answer where the next person can find it
Once you know the registry, record three things together: the chip number, the company name, and the phone number or login route for updating it. File that note with your dog's vaccination records rather than in a separate drawer, because boarding facilities, new vets, and anyone who finds your dog will all ask for the same cluster of information. Check the registry details again whenever you move house or change your phone number, and treat the check as part of the move itself. Ask also whether the record can be updated online, since that decides how quickly you can fix your details on the very night your dog actually goes missing. KinsLe's Pet Passport holds your dog's chip number and records together in one portable packet, so the registry name travels with the rest of his paperwork instead of living in a forgotten email.