Outvoicer MCP

An unofficial MCP server for preparing and creating invoice drafts in Outvoicer.

Purpose

I already use MCP servers, so connecting Outvoicer was a natural next step. Its public API makes it possible to prepare, create, and send invoices through conversation.

This project was created in collaboration with Martin Sookael, founder of Outvoicer.

I use OpenCode, but the server also works with compatible clients such as ChatGPT and Claude.

Scope

The current focus is limited to:

• Creating invoices
• Previewing invoices
• Sending invoices

Currently, it does not manage Outvoicer account data, integrations, or settings. These can be managed at outvoicer.com.

Authentication

Public lebo.agency endpoints use OAuth through oauth.lebo.agency.

The server validates signed OAuth access tokens, then resolves the user's selected Outvoicer connection server-side.

• Protected resource discovery uses RFC 9728 metadata.
• Authorization uses the OAuth authorization code flow with PKCE S256 and dynamic client registration.
• OAuth resource indicators bind authorization, access tokens, and JWT audiences to the Outvoicer MCP URL.
• JWT access tokens are verified against the authorization server's JWKS with exact issuer, audience, expiry, and scope checks.
• Tools advertise and enforce invoice:read and invoice:create independently.

Security

• Public access is protected by OAuth.
• OAuth access is limited to the Outvoicer MCP resource and the user's stored connection.
• Requests are stateless and access tokens are validated on every request.
• OAuth access tokens are never forwarded to Outvoicer.
• Responses and telemetry exclude sensitive data.

Technology

• TypeScript
• Bun runs the application and manages packages.
• Cloudflare Workers hosts the server.
• Hono handles HTTP requests, and the Model Context Protocol SDK provides MCP support.
• Zod validates data.
• Langfuse and OpenTelemetry provide tracing and observability.

About

This project is maintained by Kristjan Suursoho, who works with Outvoicer as a freelancer. It is an unofficial project and is not maintained or published by Outvoicer.

The Outvoicer API, internally known as Tetris, is available at api.outvoicer.com. OpenAPI documentation is available there.

License

Licensed under the MIT License.