QR pet tag with your details for the collar

The tag doesn't replace the microchip

Worth saying first: the microchip is mandatory for dogs throughout Spain and is what legally identifies the animal. But a microchip can only be read by a vet, an animal shelter or the police with a scanner, and someone has to take the animal there first. The tag covers the first two hours, which are what really matter: the neighbor who finds the dog in the street has no scanner, but does have a phone in their pocket.

Ideally, have both. The chip for the legal side and in case the tag is lost; the tag so your pet comes back in the same neighborhood on the same day.

What to include and what not

This is where many people get it wrong, so it's worth thinking about for two minutes.

• Include a phone number. It's the only essential. A mobile is better than a landline, and better one you always carry.
• Don't include your address. Neither in the code nor engraved. A tag with the dog's name and your home address is, literally, a sign saying who lives where. If you want to give more details, use a link to a page you control.
• Think about the engraved name. Putting the pet's name on the tag helps the finder calm it down and trust you when you call. But it also lets a stranger call it by name, and some dogs will go off with anyone who talks to them like that. Your call; many people prefer to engrave just “CALL ME” or “I BELONG TO”.
• If your pet needs medication or has a condition, that's the best reason of all to use a link instead of a bare phone number.

Phone or link: which to choose

The phone is the simplest and most robust: it works without mobile data, without internet and without depending on a web page still existing five years from now. It's the default option.

The link —to a public note, your website or a ready-made WhatsApp message— lets you say more and change it whenever you like, but it needs coverage and depends on a third-party service. If you go this way, choose something you control and also engrave your phone number in the text, as a safety net.

Size, material and mounting

Size matters more than anything else, because a small tag with a long link produces tiny squares that no phone can read. The tool shows you the real size of each square while you design and turns red below 1.5 mm. With a phone number as content the code is very short, which is why 30 mm tags work without trouble.

• 40 mm — the minimum at which a short phone number still reads comfortably. For small dogs and cats, always checking the warning.
• 45 mm — the default size and the one we recommend. Each square stays above 1.5 mm and scans first time even in low light.
• 50 mm or more — if you're going to use a link instead of a phone number, or if you also want an emoji in the center.

It may seem counterintuitive that a pet tag needs 45 mm when engraved metal tags are smaller. The reason is physical: an engraved tag only has to be readable by a person who leans in, while a QR code has to be readable by a camera half a meter away, and for that each square needs its space. The tool shows you that size in real time precisely so you don't get a surprise after printing.

About the material: PETG holds up much better than PLA against rain, sun and knocks, and for something that will hang outdoors it's worth it. Print with solid infill, 40% or more, because the piece gets tugged. And use a small snap hook instead of an open ring: it snags less in bushes.

Something worth knowing: putting an emoji or logo in the center makes the code much denser. To keep it readable with some squares covered, the system has to raise the error correction level, which multiplies the number of squares and makes them smaller. On a 30 or 35 mm tag that's enough to make it unreadable. If you want the little dog drawing in the center, go up to 45 mm or more and check the millimeters-per-square warning before printing.

A practical note: the raised plastic clinks against the microchip tag or another metal tag. If the jingling bothers your dog, put it on the harness instead of the collar, or stick a small piece of felt on the back.

Test it before relying on it

Once it's printed, scan it with two different phones, one of them not yours, and in low light. Repeat the test every few months: rubbing wears down the raised code, especially if your dog loves to roll around.