Glossary
What is an HLR lookup?
An HLR lookup queries a mobile carrier's Home Location Register, the core network database that tracks which operator a subscriber is currently registered with, whether the number is reachable, and basic routing information. It is a signalling-level technique, not an application programming interface, and it is the origin of most "is this number active" checks still sold today, including modern carrier lookup APIs that build on the same underlying data.
What the HLR actually stores
The Home Location Register is a database inside a mobile network that holds a permanent record for every subscriber issued a SIM on that network: identifiers, the services the subscriber is provisioned for, and a pointer to the Visitor Location Register currently serving the subscriber's handset. When a query reaches the HLR, it can return whether the number is provisioned and reachable, which network currently serves it, including a foreign network if the subscriber is roaming, and format-level validity.
This lookup happens over the older SS7 signalling protocol in many networks, or increasingly via HTTP-based network APIs that sit in front of the same underlying subscriber data. Either way, the result reflects live network state, not a static directory.
What an HLR lookup tells you, and what it does not
An HLR-style query is genuinely useful for confirming a number is live and identifying its current carrier. It is not a fraud signal on its own. It says nothing about whether the SIM was recently swapped, nothing about the handset, and nothing about identity. Fraud and KYC teams that treat "number is active" as equivalent to "number is safe" are missing the point of the check.
- Reachability: is the number currently provisioned and able to receive traffic
- Carrier: which network operator currently serves the number
- Roaming status: whether the subscriber is on their home network or a visited one
- Number type: whether the number is a mobile line at all, versus landline or VoIP
A recent SIM swap, by contrast, is a separate signal that an HLR-style query alone does not surface; that is a distinct check, described in Telebase's SIM swap API reference, which is launching for carrier and number type intelligence buyers who need both signals together.
How this compares to Telebase's carrier lookup
Telebase's carrier lookup API returns the same category of information an HLR query provides, active status, carrier and country, through a single HTTP request rather than legacy signalling infrastructure. The response is a plain JSON object, not a raw SS7 message, which is what makes it usable directly inside a fraud or KYC decisioning stack without a telecom integration team.