Question on intended semantics of McpResource and side effects

[vinsguru]

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Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

I have a question about the intended usage of Resource in MCP.

From the protocol, resources appear to be client-initiated and read-oriented, but there is no explicit guidance on whether resource handlers are expected to be side-effect free.

In particular:

• Is it considered acceptable for a resource handler to:
  • perform sampling (LLM calls), and
  • persist derived results (enrichment, annotations, insights) to a database?

This would not be an authoritative state change, but rather post-processing or enrichment based on existing domain events. The authoritative mutation happens elsewhere; the resource materializes insights.

I understand tools are intended for LLM-initiated actions, which makes them a poor fit for client-initiated enrichment workflows.

Is this usage:

• considered acceptable but undocumented?
• discouraged?
• or something the protocol intentionally leaves open?

Clarification on whether resources are expected to be logically read-only vs side-effect free would be very helpful.

Thanks.