MCP is a versioned protocol — client and server normally negotiate a protocol version automatically when a connection is established. MCPFlo lets you override this negotiation, which is useful when you need to test how a server behaves against a specific version rather than whatever it would pick by default.

Where to set it

The protocol version override lives in the Advanced section when adding (or editing) a server — available for both stdio and Streamable HTTP transports.

1. Click + Add Server (or edit an existing server).
2. Expand the Advanced section.
3. Enter the MCP protocol version you want to pin the connection to.
4. Save/reconnect — MCPFlo sends that version during the initial handshake instead of negotiating its own default.

Why you’d use it

• Compatibility testing — confirm a server correctly supports (or rejects) an older protocol version it claims to support.
• Regression testing — verify a server’s behavior hasn’t changed across protocol versions during development.
• Debugging negotiation issues — if a server behaves unexpectedly, pinning a version helps isolate whether the problem is version-related or something else.

Notes

• Leaving this field blank uses MCPFlo’s default negotiation behavior — most users never need to touch it.
• If a server doesn’t support the pinned version, the connection will fail or the server may respond with an error during the handshake, depending on how it implements version checking.
• This setting is per-server, not global — different servers can be pinned to different versions simultaneously.