InvoiceXML

AModel Context Protocolserver that exposes theInvoiceXML APIto AI agents. Covers Factur-X, ZUGFeRD, XRechnung, UBL / CII, and Peppol BIS Billing 3.0.

+----------------------+ ProjectReference +----------------------+ | InvoiceXml.Mcp.Core | -------------------> | InvoiceXml.Mcp.Host | | (SDK: client+tools) | | (the deployable) | +----------------------+ +----------------------+

Adding a new auth mode = one arm inAuthExtensions.csplus a small folder underAuth/<Mode>/. Adding a new tool = one[McpServerTool]class. Nothing else changes.

invoicexml-mcp/ ├── src/ │ ├── InvoiceXml.Mcp.Core/ # the SDK: client, models, tools │ │ ├── Enums/ Interfaces/ Models/ Options/ Services/ Tools/ Extensions/ │ └── InvoiceXml.Mcp.Host/ # the deployable host │ ├── Auth/{ApiKey,OAuth}/ # the two auth modes │ ├── Configuration/ │ ├── Program.cs │ └── appsettings.json # safe defaults, no secrets ├── tests/ │ ├── InvoiceXml.Mcp.Core.Tests/ │ └── InvoiceXml.Mcp.Host.Tests/ ├── Directory.Build.props # repo-wide MSBuild defaults ├── Directory.Packages.props # Central Package Management ├── global.json # pins the .NET SDK └── InvoiceXml.Mcp.slnx

You need a .NET 10 SDK and an InvoiceXML API key.

# 1. Provide your API key (pick one): # A. dotnet user-secrets (recommended — kept outside the repo) dotnet user-secrets --project src/InvoiceXml.Mcp.Host set "Mcp:ApiKey:Value" "your-key" # B. environment variable $env:INVOICEXML_API_KEY = "your-key" # 2. Run dotnet run --project src/InvoiceXml.Mcp.Host

GET http://localhost:5004/shows a welcome page in a browser; the MCP endpoint isPOST http://localhost:5004/;GET /healthreturns{ "status": "ok" }.

{ // Required in OAuth mode. The public origin where this MCP server is reachable. // Used in the protected-resource metadata response. "McpUri": "https://mcp.example.com", "InvoiceXml": { "BaseUrl": "https://api.invoicexml.com", // override for staging / local "Timeout": "00:01:40" }, "Mcp": { "AuthMode": "ApiKey", // "ApiKey" | "OAuth" "ApiKey": { "Value": "" // ApiKey mode: NEVER commit a real key }, "OAuth": { "AuthorizationServer": "https://invoicexml.com", "ScopesSupported": [ "api_token.read" ] }, "FileInput": { // limits for the URL-fetch input mode "MaxFileSizeBytes": 5242880, "FetchTimeout": "00:00:30" } } }

Environment variable equivalents (double underscore = nesting):

WhenMcp:AuthMode=OAuththe host stops accepting a static API key and instead:
- Returns401withWWW-Authenticate: Bearer resource_metadata="…"for anyPOST /that has no Bearer token.
- ServesGET /.well-known/oauth-protected-resourcepointing MCP clients atinvoicexml.comas the authorization server.
- Forwards the inbound Bearer token verbatim on every outbound call to the InvoiceXML API (the API is the source of truth for token validity; the MCP server does not validate tokens locally).

client → MCP POST / → 401 + resource_metadata client → /.well-known/oauth-protected-resource → { authorization_servers: [invoicexml.com] } client → invoicexml.com/.well-known/oauth-authorization-server → { authorize, token, register endpoints } client → invoicexml.com/oauth/register → client_id + client_secret (DCR) client → invoicexml.com/oauth/authorize → user consents, gets code client → invoicexml.com/oauth/token → access_token (= user's API key) client → MCP POST / + Authorization: Bearer → 200, tool call flows through

The host is a standard ASP.NET Core app — run it however you run .NET services (systemd, a container, a PaaS, etc.; the repo doesn't prescribe one):

dotnet publish src/InvoiceXml.Mcp.Host -c Release -o ./publish # then run ./publish/InvoiceXml.Mcp.Host on your host

Set configuration via environment variables on the host (never commit secrets):

- ASPNETCORE_ENVIRONMENT=Production
- Mcp__AuthMode=ApiKey(orOAuth)
- Mcp__ApiKey__Value=…/INVOICEXML_API_KEY=…(ApiKey mode)
- McpUri=https://your-public-urlandMcp__OAuth__AuthorizationServer=https://invoicexml.com(OAuth mode)

Terminate TLS at your reverse proxy / load balancer and forward to the host's HTTP port. The server is stateless, so you can run multiple instances behind a load balancer.

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