APIs let you interact with network devices programmatically. Instead of screen-scraping CLI output, you send structured requests and receive structured responses.
Structured data. API responses come as JSON or XML. Parsing is straightforward. CLI output varies and breaks parsers.
Defined operations. APIs document what operations exist and what parameters they accept.
Error handling. APIs return status codes and error messages. You know exactly what failed.
Common types: REST APIs (HTTP-based), NETCONF (XML over SSH), and RESTCONF (REST with YANG models).