Mcp-Param-{Name} containing invalid characters is rejected

How to fix this

Reject a recognised `Mcp-Param-{Name}` whose value contains characters outside the permitted set, rather than forwarding it to the tool.

How the validator checks this

This rule is catalogued from the specification but is not yet checked automatically. No probe emits a finding for it, so it never appears in a report as pass, warn or fail. It is documented here because it is a real requirement of the specification — it is simply not one this validator can confirm for you yet.

Check your own server against this rule

The validator makes real protocol requests and reports this rule as pass, warn or fail alongside the other 78. Validate a server or read how the check works.

Other Request metadata headers rules

• MCP-HDR-001Missing Mcp-Method rejected with 400 + HeaderMismatch
• MCP-HDR-002Missing Mcp-Name on tools/call rejected with 400 + HeaderMismatch
• MCP-HDR-003Mcp-Name header must match the request body
• MCP-HDR-004Missing MCP-Protocol-Version rejected (modern-only servers)
• MCP-HDR-005MCP-Protocol-Version header must match _meta.protocolVersion
• MCP-HDR-006Header names compared case-insensitively
• MCP-HDR-007Base64 sentinel-encoded header values decoded before comparison
• MCP-HDR-008Mcp-Param-{Name} validated against body when x-mcp-header is declared
• MCP-HDR-010Header validation runs before method dispatch