How it works

Area codes come from NANPA's central-office assignment records — the same registry carriers use — matched to cities in our directory. NANPA assigns prefixes to rate centres, not to ZIP codes or city limits, so the lookup is city-level: at a boundary, both sides' codes can apply, and a mobile number keeps its area code when its owner moves.

Many territories are served by several codes at once (an overlay): new numbers in west Los Angeles may get 310 or 424, and Manhattan spreads across 212, 646 and 332. The tool lists overlay codes with how often they appear together, so a "wrong" area code is often just the overlay.

Need this in your own software? The reverse lookup is GET /v1/areacodes/{code} on the free CodePostalPro API, and AI assistants get it as the area_code_lookup tool on our MCP server.