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How it works

The MCP protocol specifies several capabilities that an MCP server may offer. Exograph's MCP server implements the tools capability.

Here's how it works:

  1. Initialization: When an MCP client (such as Claude Desktop or VS Code) connects, it queries each configured MCP server for its capabilities (the initialization phase).

    Exograph declares the tools capability during the initialization phase.

  2. Tools discovery: For each capability declared, the MCP client asks for more details. For the tools capability, it asks for the tools list.

    Exograph responds to this request by sending the list of tools along with their descriptions. The descriptions include the GraphQL schema, which the LLM can use to form valid queries. If you added doc comments to your Exograph model, those are also included.

  3. Query Execution: When a user submits a prompt, the MCP client passes the tools information along with that prompt to the LLM. The LLM may request the MCP client to invoke tools one or more times.

    For Exograph, the tool invocation includes the GraphQL query and variables, which are invoked in the normal manner. Exograph's standard access control mechanism ensures that the LLM gets access to only the data permitted by the user.

Exograph's Tools​

By default, the MCP server operates in combined mode. In this mode, the MCP server offers a single tool: execute_query. Its description gives LLMs sufficient information to form appropriate queries. Specifically, the description includes the GraphQL schema. Exograph also offers separate mode, where it offers two tools: execute_query and introspect. To set the mode, set the EXO_MCP_MODE environment variable to separate or combined.

EXO_MCP_MODE=separate exo dev

By default, Exograph's MCP server doesn't expose any mutations (even if access control allows them). However, you can enable mutations selectively by creating a profile.

Disabling MCP API​

Exograph's MCP server is enabled by default. To disable the MCP endpoint, set the EXO_ENABLE_MCP environment variable to false.