Support for Custom Metadata in Tool Specification #1483

The current MCP protocol does not allow attaching structured metadata to tools, which limits secure and context-aware execution in enterprise scenarios.

1. **Is your feature request related to a problem? Please describe.**Currently, the MCP protocol does not support custom metadata in the tool specification. This limitation makes it difficult to handle advanced use cases such as authorization, role-based execution, scope validation, or tool-specific custom logic.
   For example:
   When different users interact with the same tool, some may only be authorized to execute read operations, while others may have permission for write or admin-level operations.
   A tool might require additional contextual metadata such as business unit, region, or tenant configuration to ensure it executes the correct logic.
   Without support for custom metadata, developers are forced to implement workarounds outside the MCP protocol, which increases complexity and reduces interoperability.

2. Describe the solution you'd like
   I would like the MCP protocol to be extendable to include custom metadata fields within the tool specification.
   Metadata can include keys such as roles, scopes, tenantId, or any custom attributes defined by the implementer. But make sure the schema is flexible for new usecases.
   At runtime, this metadata should be available for validation before tool execution, enabling secure and context-aware execution.
   The protocol should allow metadata to be optional, so basic use cases remain simple while advanced use cases can leverage it when needed.

{
  "name": "generateReport",
  "description": "Generates a report based on input filters",
  "metadata": {
    "roles": ["admin", "report_viewer"],
    "scopes": ["finance.read", "finance.write"],
    "tenantConfig": "multiTenantEnabled",
    "execution": {
      "region": "US-East",
      "priority": "high"
    }
  }
}

3. Describe alternatives you've considered

Embedding metadata in tool descriptions: Metadata can sometimes be embedded in the description field, but this is not machine-readable and cannot be reliably parsed.
External access control systems: Implementing authorization logic outside the MCP protocol works but results in fragmented responsibility and makes tool portability harder.
Custom wrapper layers: creates a wrapper services around tools to inject metadata, but this increases complexity and reduces standardization.

4. Additional context
   Adding support for metadata would unlock several scenarios:

Role-based execution – Ensure only users with appropriate roles (e.g., admin) can execute sensitive tools.
Scope validation – Verify that the tool execution aligns with the user's granted scopes (e.g., finance.read vs. finance.write).
Multi-tenant systems – Pass tenant-specific configurations to tools in a standardized way.
Custom execution logic – Metadata could provide hints about execution environment (e.g., region=US-East, priority=high).

This feature would make MCP more secure, flexible, and adaptable to enterprise-grade scenarios where context-aware execution is critical.