Connect MCP servers

MCP tools let the agent use tools served by a Model Context Protocol server. Strands harness connects them from a standard mcpServers config, the same shape other MCP clients use, and adds every discovered tool to the agent’s tool list.

Pass a config file or an inline mapping

mcp_servers accepts either a path to a JSON file or the mapping itself. The mapping can be a flat {name: {...}} map, or that map nested under an mcpServers key:

Strands harness

Python

# pip install strands-harness
from strands_harness import create_harness

# From a JSON file:
agent = create_harness(mcp_servers="./mcp.json")

# Or inline:
agent = create_harness(
    mcp_servers={
        "filesystem": {"command": "npx", "args": ["-y", "@modelcontextprotocol/server-filesystem", "."]},
    },
)

TypeScript

// npm install @strands-agents/harness
import { createHarness } from '@strands-agents/harness'

// From a JSON file:
const agent = await createHarness({ mcpServers: './mcp.json' })

// Or inline:
const inline = await createHarness({
  mcpServers: {
    filesystem: { command: 'npx', args: ['-y', '@modelcontextprotocol/server-filesystem', '.'] },
  },
})

SDK

Python

# pip install strands-agents
from mcp import stdio_client, StdioServerParameters
from strands import Agent
from strands.tools.mcp import MCPClient

# The Strands Harness SDK has no mcpServers-file loader; make a client per server.
mcp_client = MCPClient(lambda: stdio_client(
    StdioServerParameters(command="npx",
        args=["-y", "@modelcontextprotocol/server-filesystem", "."])))
agent = Agent(tools=[mcp_client])
agent("list the files in this project")

TypeScript

// npm install @strands-agents/sdk
import { Agent, McpClient } from '@strands-agents/sdk'
import { StdioClientTransport } from '@modelcontextprotocol/sdk/client/stdio.js'

// The Strands Harness SDK has no mcpServers-file loader; make a client per server.
const mcpClient = new McpClient({
  transport: new StdioClientTransport({
    command: 'npx',
    args: ['-y', '@modelcontextprotocol/server-filesystem', '.'],
  }),
})
const agent = new Agent({ tools: [mcpClient] })
await agent.invoke('list the files in this project')

The Strands Harness SDK connects each server, discovers its tools, and manages its lifecycle.

A failed server yields no tools, not a crash

Each server defaults to continuing on error, so a server that fails to start yields no tools rather than taking construction down with it. Make a specific server’s failure fatal by setting "continue_on_error": false on it in the config.

If two servers, or a server and a local tool, would register the same tool name, set a server’s "prefix" in the config so its tools are namespaced and cannot clash.

The CLI also discovers project MCP config automatically and can add config files with --mcp-config. For the full option list, see the configuration reference.