Represents the contents of a _meta field, which clients and servers use to attach additional metadata to their
interactions. Certain key names are reserved by MCP for protocol-level metadata; implementations MUST NOT make assumptions about
values at these keys. Additionally, specific schema definitions may reserve particular names for purpose-specific
metadata, as declared in those definitions. Valid keys have two segments: Prefix:
- Optional — if specified, MUST be a series of labels separated by dots (
.), followed by a slash (/).
- Labels MUST start with a letter and end with a letter or digit. Interior characters may be letters, digits, or
hyphens (
-).
- Implementations SHOULD use reverse DNS notation (e.g.,
com.example/ rather than example.com/).
- Any prefix where the second label is
modelcontextprotocol or mcp is reserved for MCP use. For example:
io.modelcontextprotocol/, dev.mcp/, org.modelcontextprotocol.api/, and com.mcp.tools/ are all reserved.
However, com.example.mcp/ is NOT reserved, as the second label is example. Name:
- Unless empty, MUST start and end with an alphanumeric character (
[a-z0-9A-Z]).
- Interior characters may be alphanumeric, hyphens (
-), underscores (_), or dots (.).