MCP

MCP

Model Context Protocol integration for local stdio servers and remote HTTP/SSE servers.

Refact’s MCP integration connects the agent to external MCP servers using the Rust SDK (rmcp). The engine supports stdio, SSE / streamable HTTP, and OAuth-based authentication for HTTP transports.

Transport support

The engine has separate transport initializers for local and remote servers:

• stdio: launches a process and connects over stdin/stdout
• SSE / streamable HTTP: connects to a remote endpoint and streams events
• streamable HTTP: used by the HTTP transport implementation in the current engine code
• OAuth 2.0 PKCE and client credentials: supported via the MCP auth layer

The default request headers include a Refact User-Agent string:

User-Agent: Refact.ai (+https://github.com/JegernOUTT/refact)

Lazy discovery

MCP tools are discovered lazily so the agent does not flood every request with every remote schema, prompt, and resource.

The intended flow is:

1. search for a tool with tool_search
2. call it with mcp_call

That keeps tool registration lightweight until a specific server capability is actually needed.

Configuration

Project-local MCP configs live under:

.refact/integrations/*.yaml

The engine also documents the same integration family in AGENTS.md and exposes integration configuration through the GUI and HTTP API.

What MCP covers

The MCP integration includes support for:

• tool registration and execution
• resources
• prompts
• sampling
• auth token persistence and refresh
• session state and reconnection settings

Related implementation files

• src/integrations/mcp/integr_mcp_stdio.rs
• src/integrations/mcp/integr_mcp_sse.rs
• src/integrations/mcp/integr_mcp_http.rs
• src/integrations/mcp/mcp_auth.rs
• src/integrations/mcp/mcp_prompts.rs
• src/integrations/mcp/mcp_resources.rs
• src/integrations/mcp/session_mcp.rs
• src/integrations/mcp/tool_mcp.rs

GUI and config surface

The MCP setup UI uses schema files such as mcp_stdio_schema.yaml, mcp_sse_schema.yaml, mcp_http_schema.yaml, and mcp_unified_schema.yaml to describe user-facing settings.

See also: Integrations, Agent Tools