syn.tax

German tax-firm workflows: clients, deadlines, documents, time tracking and DATEV data via OAuth. It is made by syn-tax.de and listed in the official MCP Registry as de.syn-tax/syn-tax. MCP (Model Context Protocol) is the open standard that lets AI apps like Claude, ChatGPT and Cursor use outside tools.

In the Claude app or claude.ai, open Settings, then Connectors, choose "Add custom connector" and paste https://actions.syn-tax.de/mcp. In Claude Code, run: claude mcp add --transport http syn-tax https://actions.syn-tax.de/mcp

ChatGPT can use remote MCP servers as connectors. In ChatGPT settings, under Apps and Connectors, turn on developer mode if asked, create a new connector and paste https://actions.syn-tax.de/mcp.

Open Cursor settings, go to MCP, choose "Add new MCP server" (or edit ~/.cursor/mcp.json) and add: { "mcpServers": { "syn-tax": { "url": "https://actions.syn-tax.de/mcp" } } }

It is online and asks you to sign in before it lists its tools, which is normal for servers tied to an account.