Protocol Versioning

Protocol Versioning ensures that MCP clients and servers can understand each other even as the standard evolves. During the initialization phase, both parties negotiate which version of the protocol to use.

Negotiation Process

1. Client Proposes: The client sends its supported versions.
2. Server Decides: The server selects the most appropriate common version.
3. Fallback: If no common version is found, the connection is gracefully closed with an error.

Versioning prevents breaking changes from disrupting existing MCP integrations.

Questions & Answers

Why is "Protocol Versioning" essential for MCP ecosystem stability?

Versioning ensures that clients (hosts) and servers can continue to communicate effectively as the protocol evolves. It prevents breaking changes from disrupting existing integrations by ensuring both parties are using a compatible set of rules.

Describe the version negotiation process during the initialization handshake.

The client begins by proposing a list of protocol versions it supports. The server then evaluates this list and selects the most appropriate common version to use for the duration of the session.

What happens if a client and server cannot agree on a common protocol version?

If the negotiation fails and no common version is found, the connection process is halted and the interaction is gracefully closed with a version mismatch error to prevent unpredictable behavior.