Esri makes ArcGIS, the most widely used GIS platform. Searches that combine Esri with ZIP codes usually want one of three things: a ZIP code boundary layer for a map, a way to geocode addresses to ZIP codes, or demographic data by ZIP. ZIPCodeLookup.io is an independent directory and is not affiliated with Esri.
ZIP code boundary layers
ArcGIS Living Atlas includes ZIP code boundary layers maintained by Esri and its data partners, with the vintage stated in each layer's description. These are estimated boundaries, since USPS defines ZIP codes as delivery routes; note the source and date when you use them.
Geocoding and reverse geocoding
The ArcGIS World Geocoding Service returns a ZIP code as part of a standardized address, and can reverse-geocode a coordinate to the nearest address. That is the right tool for exact address-level work, which a postal reference dataset cannot do.
Where this site fits
For a quick look at a ZIP's place, county association and reference point, or to list the ZIP codes in a state before building a map, use the ZIP code lookup, state directory or radius finder. For boundary and demographic layers, use the GIS platform.