What's a MAC address?
A MAC (Media Access Control) address is the 48-bit hardware identifier each network interface gets at manufacture time. Wi-Fi cards, Ethernet ports, and Bluetooth radios all carry one. The first 24 bits — the OUI — identify the manufacturer, and they're assigned by the IEEE.
Notation
We accept any reasonable input: 3C:5A:B4:00:00:00, 3c-5a-b4-00-00-00, 3c5ab4.000000, or raw hex. As long as you give us 12 hex digits, we'll normalise it.
The "locally administered" bit
Bit 1 of the first octet flips between universally administered (IEEE assigned) and locally administered (you, your VM hypervisor, your phone when it rotates a privacy MAC, your switch when it impersonates one, …). Privacy MACs and software-defined VMs always have this bit set, which is why they don't resolve to a vendor.
Data source
We forward your query to macvendors.com (free, no auth, ~1 req/s rate limit). Their dataset is built from the public IEEE OUI registry. Edge-cached for an hour.
JSON API
GET /api/mac/3C:5A:B4:00:00:00 returns the same payload plus the parsed-MAC flags. Example.