IDL
Interface Definition Language: a schema that defines the contract between client and server. Protobuf, Thrift, and OpenAPI are IDLs that generate client/server code.
What is IDL?
Interface Definition Language: a schema that defines the contract between client and server. Protobuf, Thrift, and OpenAPI are IDLs that generate client/server code.
IDL is a intermediate-level concept that sits in the API Design & Protocols area of system design. Engineers reach for it whenever they need to reason about real-world trade-offs in that space — not just for textbook correctness, but because real production systems at companies like Netflix, Amazon, and Google make these decisions every day.
If you want to go deeper than this definition — with diagrams, code, and a quiz to lock it in — work through the "IDL" lesson linked below. It walks through the why, the mechanism, the trade-offs, and how the giants actually use it in production.
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See also
Related glossary terms you might want to look up next.
Protocol Buffers
Google's language-neutral, binary serialization format. Smaller and faster than JSON. Defines schemas in .proto files that generate typed code for any language.
gRPC
A high-performance RPC framework by Google using Protocol Buffers and HTTP/2. Much faster than REST for service-to-service communication.
REST API
An architectural style for building APIs using standard HTTP methods (GET, POST, PUT, DELETE). Resources are identified by URLs.