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NPA-NXXs (CO codes)

Area codes (NPAs) within the North American Numbering Plan (NANP), are further divided into NXXs, often called "Exchanges" or "CO codes". The NXX is the 3 digits that immediately follow the area code.

Each NPA-NXX is associated with a specific rate center, which means that each NPA-NXX is associated with a specific state and country.

With certain exceptions, the following NXXs are reserved or prohibited from assignment:

  • NXXs can not start with 0 or 1, due to historical considerations related to 7-digit dialing
  • 211, 311, 411, 511, 611, 711, 811, and 911 are reserved for 3-digit "N11" dialing
  • 555 is reserved for directory assistance (555-1212) and fictional numbers
  • 950, 958, and 959 are reserved for legacy PSTN features
  • 976 is reserved for premium-rate calling services

As a result, there are approximately 787 NXXs per NPA, which yield 7.87 million usable TNs per NPA.

Common uses for this API are to determine the rate center corresponding to a given NPA-NXX:

GET /api/npaNxxs/858380

To determine all NPA-NXXs corresponding to a given rate center:

GET /api/npaNxxs/?rateCenter=POWAY&state=CA

While we make every effort to keep this data accurate and up-to-date, your mileage may vary. Please contact api-support@numberbarn.com with any comments, concerns, or corrections.