n8n MCP Server: Connect Claude/ChatGPT to wFirma & KSeF Invoicing

Connect Claude/ChatGPT to Polish invoicing—directly from n8n

This n8n MCP Server lets any MCP client (like Claude or ChatGPT) safely access wFirma invoicing and accounting tools. In plain terms: you can search, read, edit, and manage documents in wFirma through an MCP interface—while a built-in approval/confirmation guard protects irreversible KSeF actions.

What this workflow does

1) MCP Server Trigger + n8n User Auth (OAuth2)
The workflow exposes 9 MCP tools. Users sign in with their n8n account via OAuth2, and only authorized people can run the workflow.

2) One workflow import, routed requests
Each tool call uses a gateway tied to $workflow.id, so you import one file. A Plan node builds the wFirma API URL and checks whether the call needs approval; Route sends it to the API, the approval guard, or the docs branch.

3) XML-to-API requests and clean JSON responses
The workflow uses an XML node to convert requests into wFirma XML, sends them via HTTP, then parses responses back into JSON (ok, status, records, pagination).

4) Safe handling of irreversible KSeF operations
Deleting records, emailing invoices, fiscalization, and final invoices sent to KSeF require confirmed=true. Otherwise the workflow returns CONFIRMATION_REQUIRED, forcing the model to ask the user first.

5) Rate-limit resilience for reads
If wFirma rate-limits find/get, the workflow waits 35 seconds and retries once. Writes are not auto-retried.

Use cases

• Ask an MCP client to search and retrieve invoices from wFirma and return paginated results.
• Use MCP to edit invoice data, manage contractors, and handle payments/expenses.
• Fetch wFirma official API module docs on demand and get XML examples in Markdown (wfirma_docs).
• Generate workflows that prevent accidental irreversible actions—KSeF finalization requires explicit user confirmation.

Technical details

• MCP Server Trigger with n8n User Auth (OAuth2)
• Tools: 9 tools covering ~40 wFirma API modules (invoices, contractors, payments, expenses, and more)
• n8n nodes/logic: if, set, xml, wait, switch, markdown
• Implements an internal Plan/Route flow per $workflow.id and parses XML responses into JSON
• Includes wfira docs fetching of the official Postman collection content as Markdown