Add instructions support to MCP::Server
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The response of the `init` method can include `instructions`. https://modelcontextprotocol.io/specification/2025-06-18/basic/lifecycle `instructions` appear to be supported starting from the 2025-03-26 specification. - https://modelcontextprotocol.io/specification/2025-03-26/basic/lifecycle (supports `instructions`) - https://modelcontextprotocol.io/specification/2024-11-05/basic/lifecycle (does not support `instructions`) If `instructions` is used with an unsupported protocol version, an `ArgumentError` will be raised. As additional context, the TypeScript SDK also treats `instructions` as optional. https://github.com/modelcontextprotocol/typescript-sdk/blob/1.16.0/src/types.ts#L356-L361
koic
commented
Jul 24, 2025
| if @configuration.protocol_version == "2024-11-05" && @instructions | ||
| message = "`instructions` supported by protocol version 2025-03-26 or higher" | ||
| raise ArgumentError, message | ||
| end |
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If accepting the instructions parameter with the older "2024-11-05" protocol version is considered preferable, this logic could be removed as it only introduces unnecessary complexity.
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Motivation and Context
The response of the
initmethod can includeinstructions. https://modelcontextprotocol.io/specification/2025-06-18/basic/lifecycleinstructionsappear to be supported starting from the 2025-03-26 specification.instructions)instructions)If
instructionsis used with an unsupported protocol version, anArgumentErrorwill be raised.How Has This Been Tested?
Existing tests have been updated and new tests have been added.
Breaking Changes
None.
Types of changes
Checklist
Additional context
As additional context, the TypeScript SDK also treats
instructionsas optional. https://github.com/modelcontextprotocol/typescript-sdk/blob/1.16.0/src/types.ts#L356-L361