Online MIB Browser (SNMP): OID Lookup & SNMP MIB Viewer
Online MIB Browser @ BestMonitoringTools.com is the biggest SNMP MIB database with 15000+ valid MIB files available freely for viewing with a user-friendly online SNMP object navigator.
You do not need MIB to OID converter, or any offline tools (MIB reader, OIDviewer, MIBexplorer, MIB walk, etc.) because for every MIB you can view SNMP OID list in the form of a MIB tree. MIB tree contains object name, object ID (OID), object data type, type of permission (maxaccess), and description for every MIB object.
Download any MIB in format of your choosing (.mib, .csv, .json, .yaml) or perform MIB, Object, SNMP OID, or vendor lookup with "match any" or "match exact" option.
And lastly, if you need help with understanding how SNMP works (MIBs, OIDs, Agents ..) please check this step-by-step guide.