MCP Server for AI Assistants

The Model Context Protocol (MCP) is an open standard that lets AI assistants use tools on your computer. The iw Toolbox is itself an MCP server. An assistant such as Claude Code or Claude Desktop can use it to check domains, narrow down mail problems and explain findings, with the same checks as in the app.

A typical flow: you ask the assistant to find out why a domain’s mail lands in spam. It calls the mail report and the blacklist check, reads the findings and suggests the right DNS records.

The tools

Tool	What it does	License
dns_lookup	DNS records of a name, like dig	free
mx_lookup	mail servers with addresses and reverse DNS	free
reverse_dns	PTR record of an IP with forward confirmation	free
domain_full_report	full report for a domain	required
mail_domain_report	MX, SPF, DMARC, DKIM, BIMI, MTA-STS	required
spf_check, dmarc_check, dkim_check, bimi_check, mta_sts_check	the individual mail checks	required
blacklist_check	IP or domain against DNS blacklists	required
dnssec_check, dns_propagation, ns_check, dns_trace, axfr_check	DNS checks	required
whois, ip_info	registration and network owner	required
http_check, tls_check, smtp_check, port_check	web, TLS, mail server, ports	required
ping, traceroute	via the operating system’s programs	required

Each tool returns the findings with explanations, the check’s tables and the dig commands to reproduce the result. For all DNS tools, the assistant can choose a server with resolver: an IP address or doh:<provider> (cloudflare, google, quad9, adguard, dns0, opendns). Without it, the server queries Cloudflare 1.1.1.1. The resolver choice from the app’s settings doesn’t apply here.

The server in the app

While the desktop app is running, it offers the MCP server at

http://127.0.0.1:8789/mcp

The assistant connects over HTTP (MCP “Streamable HTTP”) and authenticates with a token. No extra program is needed.

Setup

Open Einstellungen › MCP-Server (Settings › MCP server). There you’ll find:

• the MCP-Endpunkt anbieten (offer MCP endpoint) switch, on by default,
• the Endpunkt (endpoint),
• a ready-made command for Claude Code,
• the ready-made entry for Claude Desktop,
• the Neues Token (new token) button.

For Claude Code, copy the command and run it in the terminal. It looks like this:

claude mcp add --transport http toolbox http://127.0.0.1:8789/mcp \
  --header "Authorization: Bearer <token>"

Claude Desktop only launches local programs. There you connect the address via npx mcp-remote, which requires Node.js. The app shows the entry for claude_desktop_config.json ready to copy. Set up other MCP clients with the address and the Authorization header.

License

Tools that require a license use the app’s license. If no valid one is entered, the server responds that the check needs an inwendo license. The three free tools always work.

Token and port

• The server is only reachable via 127.0.0.1, so only from your own computer.
• Every request needs the token. Without it, or with a wrong one, the server answers „Zugriffstoken fehlt oder ist falsch“ (access token missing or wrong).
• Neues Token replaces the token. The old one stops working immediately, and you need to set up connected assistants again with the new command.
• On macOS the token is stored in the Keychain.
• If port 8789 is in use, the app falls back to a free port and shows in the settings that this address is only valid until the next launch.

The app has to be running for the assistant to reach it. When you quit it, the server is gone too.

The server without the app (stdio)

For developers who build the Toolbox from source, the server is also available as a standalone program, toolbox-mcp. The assistant launches it itself and talks to it over stdio. The app doesn’t need to be running.

./tool/install_mcp.sh          # builds to ~/.local/bin/toolbox-mcp
claude mcp add toolbox -- ~/.local/bin/toolbox-mcp

install_mcp.sh needs Flutter or Dart. Checks that require a license need the license key here, either in the environment variable IW_TOOLBOX_LICENSE or as the argument --license-key <key>. The program verifies it with inwendo’s license server on the first licensed call.

Security

The tools only read. They don’t change DNS records or send mail. They do make real connections, though: DNS queries, HTTP requests, connections to mail servers, port checks, ping and traceroute. A port check against someone else’s server may show up there as a scan. Keep an eye on your MCP client’s permissions. What the assistant passes on to its provider is governed by that provider’s terms.