MCP Tool Integration

Agent objective

Produce a builder with MCP servers correctly configured — right transport, Docker lifecycle, and auth — so the agent can discover and call MCP tools transparently.

When to load this skill

• Adding external tools via MCP (GitHub, filesystem, databases, web APIs)
• Connecting to Docker-hosted MCP servers
• Debugging MCP connection or tool discovery failures
• Building agents that use context7, GitHub MCP, or custom MCP servers

Implementation baseline

import { ReactiveAgents } from "@reactive-agents/runtime";

const agent = await ReactiveAgents.create()
  .withProvider("anthropic")
  .withReasoning({ defaultStrategy: "adaptive" })
  .withMCP([
    {
      name: "github",
      command: "docker",
      args: [
        "run", "--rm", "-i",
        "-e", "GITHUB_PERSONAL_ACCESS_TOKEN",
        "ghcr.io/github/github-mcp-server",
      ],
      env: { GITHUB_PERSONAL_ACCESS_TOKEN: process.env.GITHUB_TOKEN ?? "" },
    },
    {
      name: "filesystem",
      command: "docker",
      args: [
        "run", "--rm", "-i",
        "-v", `${process.cwd()}:/workspace`,
        "mcp/filesystem", "/workspace",
      ],
      // transport auto-inferred as "stdio" (command present, no endpoint)
    },
  ])
  .build();

.withMCP() implicitly enables the tools layer — .withTools() is not required before it.

Key patterns

Two Docker MCP patterns

Pattern A — stdio MCP (GitHub MCP, filesystem MCP): reads JSON-RPC from stdin

.withMCP({
  name: "github",
  command: "docker",
  args: ["run", "--rm", "-i", "ghcr.io/github/github-mcp-server"],
  env: { GITHUB_PERSONAL_ACCESS_TOKEN: process.env.GITHUB_TOKEN ?? "" },
  // transport: inferred as "stdio" — "-i" keeps stdin open for JSON-RPC
})

Pattern B — HTTP-only MCP (context7, etc.): starts HTTP server, ignores stdin

.withMCP({
  name: "context7",
  command: "docker",
  args: ["run", "--rm", "-p", "3000:3000", "ghcr.io/upstash/context7-mcp"],
  // Framework auto-detects HTTP URL printed to stderr → switches to port-mapped HTTP
  // Do NOT hardcode transport here — let auto-detection handle it
})

Transport auto-detection

When a stdio Docker container prints an HTTP URL to stderr, the MCP client races the stdio connection against HTTP URL detection. HTTP wins → client switches to port-mapped HTTP mode automatically.

Two container phases are created:

• rax-probe-<name>-<pid> — initial stdio probe attempt
• rax-mcp-<name>-<pid> — port-mapped HTTP managed container (if HTTP detected)

PID-based naming prevents conflicts when multiple agents run concurrently.

Transport field (optional — usually omit)

// Auto-inferred rules:
// command present, no endpoint → "stdio"
// endpoint ends with /mcp     → "streamable-http"
// endpoint (other path)       → "sse"

// Only set transport explicitly when overriding detection:
.withMCP({ name: "my-server", endpoint: "http://localhost:3000/api", transport: "sse" })

Non-Docker MCP (local process or remote HTTP)

// Local process
.withMCP({ name: "my-mcp", command: "node", args: ["./my-mcp-server.js"] })

// npx
.withMCP({ name: "fs", command: "npx", args: ["-y", "@modelcontextprotocol/server-filesystem", "/workspace"] })

// Remote Streamable HTTP
.withMCP({ name: "remote", endpoint: "https://mcp.example.com/mcp" })

// Remote SSE with auth header
.withMCP({ name: "secure", endpoint: "https://mcp.example.com/sse", headers: { Authorization: `Bearer ${process.env.API_KEY}` } })

Container lifecycle

The framework owns container lifecycle:

• docker run starts the container when the agent is built
• On agent dispose, docker rm -f <containerName> stops it

Critical: docker rm -f is the only reliable way to stop MCP Docker containers. Killing the docker run process leaves the container alive in the Docker daemon.

MCPServerConfig reference

Field	Type	Required	Notes
name	string	Yes	Unique identifier for this server
command	string	For stdio	Executable ("docker", "node", "npx", etc.)
args	string[]	For stdio	Command arguments
env	Record<string, string>	No	Environment variables merged over process.env
cwd	string	No	Working directory for the subprocess
endpoint	string	For HTTP	URL of the MCP HTTP endpoint
headers	Record<string, string>	No	HTTP auth headers for remote endpoints
transport	"stdio"|"streamable-http"|"sse"	No	Auto-inferred if omitted

Pitfalls

• subprocess.kill() does not stop Docker containers — only docker rm -f works
• Don't hardcode transport: "streamable-http" for HTTP-only Docker servers — let auto-detection handle it
• Container names are PID-scoped — don't try to reference them manually
• Each agent creates its own containers — 10 parallel agents = 10 container instances
• MCP tools are discovered at connection time — if the server isn't ready at build time, tool discovery silently fails
• env values must be strings — use process.env.VAR ?? "" pattern, never pass undefined
• stdio Pattern A requires -i in the docker args to keep stdin open; HTTP Pattern B requires -p PORT:PORT for host access