Configuration

Basic Configuration

To enable MCP in your Cosmo Router, add the following to your config.yaml:

mcp:
  enabled: true
  server:
    listen_addr: 'localhost:5025'
  graph_name: 'my-graph'
  exclude_mutations: true
  storage:
    provider_id: 'mcp'

storage_providers:
  file_system:
    - id: 'mcp'
      path: 'operations'

Configuration Options

Option	Description	Default
`enabled`	Enable or disable the MCP server	`false`
`server.listen_addr`	The address and port where the MCP server will listen for requests	`localhost:5025`
`server.base_url`	The public base URL of the MCP server. Required when OAuth is enabled. Used for the RFC 9728 metadata endpoint and `resource_metadata` in `WWW-Authenticate` headers. Set this to your externally-reachable URL when behind a reverse proxy or load balancer.	-
`router_url`	Custom URL to use for the router GraphQL endpoint in MCP responses. Use this when your router is behind a proxy.	-
`storage.provider_id`	The ID of a storage provider to use for loading GraphQL operations. Only `file_system` providers are supported.	-
`session.stateless`	Whether the MCP server should operate in stateless mode. When `true`, no server-side session state is maintained between requests.	`true`
`graph_name`	The name of the graph this router exposes via MCP. Converted to kebab-case and used to build the MCP server name (`wundergraph-cosmo-<kebab-case-name>`) and for logging; it does not select a different graph. For example, `MyGraph` becomes `wundergraph-cosmo-my-graph`.	`mygraph`
`exclude_mutations`	Whether to exclude mutation operations from being exposed	`false`
`enable_arbitrary_operations`	Enables the `execute_graphql` built-in tool, allowing clients to run arbitrary GraphQL operations beyond the pre-defined operation set.	`false`
`expose_schema`	Enables the `get_schema` built-in tool, exposing the full GraphQL schema to MCP clients.	`false`
`omit_tool_name_prefix`	When enabled, MCP tool names omit the `execute_operation_` prefix. For example, `GetUser` becomes `get_user` instead of `execute_operation_get_user`. See Operations - Omitting the Tool Name Prefix.	`false`

For OAuth-specific configuration, see OAuth 2.1 Authorization.

Environment Variables

All MCP options can also be set via environment variables:

Environment Variable	Configuration Path
`MCP_ENABLED`	`mcp.enabled`
`MCP_SERVER_LISTEN_ADDR`	`mcp.server.listen_addr`
`MCP_SERVER_BASE_URL`	`mcp.server.base_url`
`MCP_ROUTER_URL`	`mcp.router_url`
`MCP_STORAGE_PROVIDER_ID`	`mcp.storage.provider_id`
`MCP_SESSION_STATELESS`	`mcp.session.stateless`
`MCP_GRAPH_NAME`	`mcp.graph_name`
`MCP_EXCLUDE_MUTATIONS`	`mcp.exclude_mutations`
`MCP_ENABLE_ARBITRARY_OPERATIONS`	`mcp.enable_arbitrary_operations`
`MCP_EXPOSE_SCHEMA`	`mcp.expose_schema`
`MCP_OMIT_TOOL_NAME_PREFIX`	`mcp.omit_tool_name_prefix`

For OAuth-related environment variables, see OAuth Configuration Reference.

Storage Providers

MCP loads operations from a configured storage provider. Currently, only the file_system provider is supported:

storage_providers:
  file_system:
    - id: 'mcp'
      path: 'operations' # Relative to the router binary

Then reference this storage provider in your MCP configuration:

mcp:
  storage:
    provider_id: 'mcp'

A storage provider must be specified to load GraphQL operations. See Storage Providers for more details on configuring storage providers.

Session Handling

The MCP server uses the Streamable HTTP transport and maintains per-session state via the Mcp-Session-Id header. When deploying multiple Router instances, you need sticky sessions to ensure all requests for a session reach the same instance. To configure sticky sessions:

The Router returns a unique Mcp-Session-Id response header when a session is established
Clients must include that value in subsequent requests as the Mcp-Session-Id request header
Your load balancer or reverse proxy must route requests with the same Mcp-Session-Id to the same instance

For details, see your load balancer or reverse proxy documentation (e.g., F5 NGINX Plus - MCP Session Affinity).

CORS

The MCP server automatically configures CORS to allow cross-origin requests from MCP clients. It sets Access-Control-Allow-Origin: * and allows the required MCP headers (Mcp-Protocol-Version, Mcp-Session-Id, Authorization, Last-Event-ID). The Mcp-Session-Id and WWW-Authenticate headers are exposed in responses. If you have additional CORS headers configured on the router, they are merged with the MCP-specific headers.

Full Configuration Example

mcp:
  enabled: true
  server:
    listen_addr: 'localhost:5025'
  router_url: 'https://your-public-router-url.example.com/graphql'
  graph_name: 'my-graph'
  exclude_mutations: true
  enable_arbitrary_operations: false
  expose_schema: false
  omit_tool_name_prefix: false
  storage:
    provider_id: 'mcp'

storage_providers:
  file_system:
    - id: 'mcp'
      path: 'operations'

Getting Started

Concepts

Cosmo Connect

Cosmo ConnectRPC

Router

Studio

Control Plane

GraphQL / Federation

Deployments and Hosting

Basic Configuration

Configuration Options

Environment Variables

Storage Providers

Session Handling

CORS

Full Configuration Example

​Basic Configuration

​Configuration Options

​Environment Variables

​Storage Providers

​Session Handling

​CORS

​Full Configuration Example

Basic Configuration

Configuration Options

Environment Variables

Storage Providers

Session Handling

CORS

Full Configuration Example