> ## Documentation Index
> Fetch the complete documentation index at: https://developers.myhero.so/llms.txt
> Use this file to discover all available pages before exploring further.

# Open an MCP server-sent event stream

> Opens a server-sent event stream for an existing MCP session identified by the required `mcp-session-id` header.

Used by MCP clients to receive server-initiated messages over the Streamable HTTP transport.



## OpenAPI

````yaml get /mcp
openapi: 3.1.0
info:
  title: HERO API
  version: current
  description: |-
    The HERO REST API.

    See https://developers.myhero.so for the rendered docs.
servers:
  - url: https://app.myhero.so
security: []
paths:
  /mcp:
    get:
      tags:
        - MCP
      summary: Open an MCP server-sent event stream
      description: >-
        Opens a server-sent event stream for an existing MCP session identified
        by the required `mcp-session-id` header.


        Used by MCP clients to receive server-initiated messages over the
        Streamable HTTP transport.
      operationId: mcpHttpGet
      parameters:
        - schema:
            type: string
          required: true
          name: mcp-session-id
          in: header
      responses:
        '200':
          description: Server-sent events stream.
          content:
            text/event-stream:
              schema:
                type: string
        '400':
          description: Mcp-Session-Id header missing.
          content:
            application/json:
              schema:
                type: object
                properties:
                  error:
                    type: string
                    description: |-
                      Error class name (e.g.

                      ValidationError, NotFound)
                  message:
                    type: string
                    description: Human-readable error message
                  details:
                    type: array
                    items: {}
                required:
                  - error
                  - message
        '403':
          description: Session belongs to a different user.
          content:
            application/json:
              schema:
                type: object
                properties:
                  error:
                    type: string
                    description: |-
                      Error class name (e.g.

                      ValidationError, NotFound)
                  message:
                    type: string
                    description: Human-readable error message
                  details:
                    type: array
                    items: {}
                required:
                  - error
                  - message
        '404':
          description: No active session for the given session ID.
          content:
            application/json:
              schema:
                type: object
                properties:
                  error:
                    type: string
                    description: |-
                      Error class name (e.g.

                      ValidationError, NotFound)
                  message:
                    type: string
                    description: Human-readable error message
                  details:
                    type: array
                    items: {}
                required:
                  - error
                  - message
      security:
        - oauth2: []
components:
  securitySchemes:
    oauth2:
      type: oauth2
      flows:
        authorizationCode:
          authorizationUrl: https://app.myhero.so/oauth/authorize
          tokenUrl: https://app.myhero.so/oauth/token
          scopes: {}

````