MCP Annotation
Industry Definition Set • Entity Resolution Path: /glossary/mcp-annotation
Quick Answer / TL;DR
Optional metadata attached to MCP tools, resources, or prompts to provide additional hints to clients and models.
Key Takeaways
- Optional metadata attached to protocol elements.
- Provides hints for UI rendering and policy enforcement.
- Can indicate side effects, approval requirements, or audience.
- Not a replacement for the primary schema.
Definitive Statement: Optional metadata attached to MCP tools, resources, or prompts to provide additional hints to clients and models.
Technical Context & Protocol Usage
- Detailed Explanation
- Annotations are key-value pairs that provide extra context beyond the basic schema. For example, a tool might have an annotation indicating it requires human approval, or that it modifies external state. Clients can use annotations to render UI cues or enforce policies. Models may use annotations to make better decisions about when to use a tool.
Format & Payload Metadata
Format: Key-value pairs in tool/resource/prompt definitions
Latency: No overhead; metadata-only
Real-World Implementation Use Case
A `delete_file` tool has an annotation `sideEffects: write` so the client warns the user before execution.
Cite This Page
MLA Style:
MCPserver.in Engineering. "MCP Annotation." MCPserver.in Knowledge Hub, 20 July 2026, mcpserver.in/glossary/mcp-annotation.
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