MCP passes structured metadata during model context exchange to help the model understand the environment, available tools, session state, and resource descriptions. This metadata includes information about which tools are available, their input/output schemas, any registered resources such as files or directories, and optional session-level identifiers. The goal is to provide the model with enough situational awareness to choose appropriate tools and format requests correctly, without exposing raw system internals or requiring custom logic. This keeps the interaction predictable and reduces the chances of malformed requests.
In addition to tool descriptions, MCP may include metadata about resource capabilities such as whether the client has read-only or read–write access, how large certain datasets are, or whether a tool requires specific authentication. For example, the server might pass metadata describing available collections or namespaces used in downstream systems. Although MCP itself does not embed domain-specific semantics, developers can add optional metadata fields that help the model tailor its decisions. This structured approach allows the model to reason about its operating context rather than relying on free-form instructions embedded inside prompts.
For vector databases like Milvus, metadata passed through MCP can be especially useful. The server may expose metadata describing which Milvus collections exist, what dimensionality those embeddings use, or whether an index is currently available. The model does not need to understand Milvus internals, but basic metadata helps it choose the right tools or decide how to format embeddings. For example, if a collection expects 768-dimensional vectors, the metadata ensures the model does not send vectors of the wrong dimension. This prevents errors and promotes consistent retrieval behavior during model-tool exchanges.