Most parcel carriers use structured tracking numbers: a fixed length, a recognisable prefix, and often a check digit. That structure is what makes automatic carrier detection possible without querying anyone's API.
The patterns
- Canada Post domestic numbers are typically 16 digits, while international items often follow the universal postal format of two letters, nine digits and the two-letter country code.
- UPS numbers usually begin with 1Z followed by an account and service segment.
- FedEx uses numeric numbers of several fixed lengths, commonly 12 or 15 digits.
- DHL Express air waybills are typically 10 digits.
- Purolator, Canpar and Intelcom each use their own fixed-length formats, which is why a number can look ambiguous until length and prefix are checked together.
Why detection sometimes picks the wrong one
Some formats genuinely overlap — a bare numeric string of the right length can be valid for more than one carrier. Good detection returns the most likely match and the plausible alternatives instead of pretending to be certain. When a retailer hands off the final mile to another carrier, the original number may also stop updating even though the parcel is moving.
Before you conclude a number is invalid
- Remove spaces, dashes and any leading label text you copied by accident.
- Check for confused characters: capital O against zero, capital I against one.
- Wait for the first carrier scan. A number issued at label creation returns nothing until the parcel is physically accepted.