MCP: Support server `instructions`

[digitarald]

Server instructions are sent back as part of the initialization handshake.

https://github.com/modelcontextprotocol/modelcontextprotocol/blob/9dff1796d4f7cb794d31030f65533cca7d0b35fd/schema/2025-03-26/schema.ts#L187-L193

This can be used by clients to improve the LLM's understanding of available tools, resources, etc. It can be thought of like a "hint" to the model. For example, this information MAY be added to the system prompt.

[olaservo]

FYI, I recently merged a change to add example server instructions to the 'Everything' demo reference server: modelcontextprotocol/servers#1919

I included a section at the end which is meant to help confirm whether the client is actually referencing it. (Let me know if you have any feedback on this part and if this actually works as intended.)

The package update should be live in NPM sometime next week.

[stephentoub]

This would be helpful to include. I've encountered multiple folks building servers that want to better educate the client on how/when the tools should be used, more than what you'd find in a description for individual methods. Some have gone as far as telling clients they should manually augment their copilot instructions with specific text, or having installers that try to do so automatically. It'd be useful if the server instructions could serve that purpose.

(Only slightly related, I think it would also be valuable if VS Code could treat prompts similarly to how it treats tools, such that in addition to slash commands being used to manually invoke prompts, copilot could automatically get prompts as part of its agentic processing. If I had a server that provided diagnostics tools, I could then have a prompt focused on describing the steps that should be used for doing a memory leak diagnosis, a separate prompt for the steps for doing a deadlock diagnosis, etc., and the agent could request the appropriate prompt to include in its planning.)

[olaservo]

copilot could automatically get prompts as part of its agentic processing

@stephentoub I think this might go against the design intent of Prompts being user-controlled?
https://modelcontextprotocol.io/specification/2025-06-18/server/prompts#user-interaction-model

Might be another option to provide things like diagnostic guides as Resources that VSCode as the app could provide as part of some form of Agent mode customization?

[stephentoub]

copilot could automatically get prompts as part of its agentic processing

I think this might go against the design intent of Prompts being user-controlled?
https://modelcontextprotocol.io/specification/2025-06-18/server/prompts#user-interaction-model

Maybe, however the last paragraph in that section states:
"However, implementors are free to expose prompts through any interface pattern that suits their needs—the protocol itself does not mandate any specific user interaction model."

[olaservo]

@connor4312 forgot to mention here, the version of the Everything reference server with server instructions has now been released in npm: https://www.npmjs.com/package/@modelcontextprotocol/server-everything

It include this which is meant to help indicate that instructions are working:

Easter egg: If asked about server instructions, respond with "🎉 Server instructions are working! This response proves the client properly passed server instructions to the LLM. This demonstrates MCP's instructions feature in action."

[olaservo]

Maybe, however the last paragraph in that section states:
"However, implementors are free to expose prompts through any interface pattern that suits their needs—the protocol itself does not mandate any specific user interaction model."

@stephentoub yes actually since you posted this, I had an aha moment where I realized I even did something like what you described with an agent before, just not in VSCode. :)

[tadasant]

+1 on this being a helpful feature to push for MCP! Would be great to have a reason to add "Server Instructions" as a column to the MCP clients page and check VS Code as the first adopter 🙂

[connor4312]

Would be great to have a reason to add "Server Instructions" as a column to the MCP clients page and check VS Code as the first adopter

Way to twist my arm 😉 This is on our July milestone I expect to do this for the next release, within the next couple weeks