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MCP Tooling Guide

MCP tooling is split into two explicit modes: Remote (HTTP) and Local (stdio). They map to tooling.type: mcp_remote and tooling.type: mcp_local. The legacy type: mcp schema is no longer supported.

1. Mode overview

Mode Tooling type When to use Key fields
Remote mcp_remote A hosted HTTP(S) MCP server (FastMCP, Claude Desktop Connector, custom gateways) server, headers, timeout
Local mcp_local A local executable that speaks MCP over stdio (Blender MCP, CLI tools, etc.) command, args, cwd, env, timeouts

2. McpRemoteConfig

Field Description
server Required. MCP HTTP(S) endpoint, e.g. https://api.example.com/mcp.
headers Optional. Extra HTTP headers such as Authorization.
timeout Optional per-request timeout (seconds).

YAML example

nodes:
  - id: remote_mcp
    type: agent
    config:
      tooling:
        type: mcp_remote
        config:
          server: https://mcp.mycompany.com/mcp
          headers:
            Authorization: Bearer ${MY_MCP_TOKEN}
          timeout: 15

DevAll connects to the URL for each list/call request and passes headers. If the server is unreachable, an error is raised immediately—there is no local fallback.

3. McpLocalConfig fields

mcp_local declares the process arguments directly under config:

  • command / args: executable and arguments (e.g., uvx blender-mcp).
  • cwd: optional working directory.
  • env / inherit_env: environment overrides.
  • startup_timeout: max seconds to wait for wait_for_log.
  • wait_for_log: regex matched against stdout to mark readiness.

YAML example

nodes:
  - id: local_mcp
    type: agent
    config:
      tooling:
        type: mcp_local
        config:
          command: uvx
          args:
            - blender-mcp
          cwd: ${REPO_ROOT}
          wait_for_log: "MCP ready"
          startup_timeout: 8

DevAll keeps the process alive and relays MCP frames over stdio.

4. FastMCP sample server

mcp_example/mcp_server.py:

from fastmcp import FastMCP
import random

mcp = FastMCP("Company Simple MCP Server", debug=True)

@mcp.tool
def rand_num(a: int, b: int) -> int:
    return random.randint(a, b)

if __name__ == "__main__":
    mcp.run()

Launch:

uv run fastmcp run mcp_example/mcp_server.py --transport streamable-http --port 8010
  • Remote mode: set server to http://127.0.0.1:8010/mcp.
  • Local mode: run the script with transport=stdio and point command to that invocation.

5. Security & operations

  • Network exposure: Remote mode should sit behind HTTPS + ACL/API keys. Local mode still has access to the host filesystem, so keep the script sandboxed.
  • Resource cleanup: Local mode processes are terminated by DevAll; make sure they gracefully handle SIGTERM/SIGKILL.
  • Logs: Emit a clear readiness line that matches wait_for_log to debug startup issues.
  • Auth: Remote mode handles tokens via headers; Local mode can receive secrets via env (never commit them).
  • Multi-session: If the MCP server is single-tenant, cap concurrency (e.g., max_concurrency=1) and share the same YAML config.

6. Debugging checklist

  1. Remote: ping the HTTP endpoint via curl or fastmcp client. Local: run the binary manually and confirm the readiness log.
  2. Start DevAll (optionally with --reload) and observe backend logs for tool discovery.
  3. When calls fail, inspect the Web UI tool traces or the structured logs under logs/.