OAuth2, Two APIs, and Soft Deletes — Building an MCP Server for FreshBooks

Most MCP servers assume your target API hands you an API key and gets out of the way. FreshBooks doesn't. It requires full OAuth2, splits its API across two different base URLs, and has resources that can only be soft-deleted. Building this server meant solving problems most MCP tutorials don't prepare you for. The result: 25 tools covering invoices, clients, expenses, payments, time tracking, projects, estimates, and reports — with the auth flow, API quirks, and deletion edge cases handled for you. What It Does MCP lets AI assistants interact with external tools directly. With this server installed, you manage your entire freelance business without leaving your AI assistant. Before (manual): Log into FreshBooks Navigate to Invoices → find overdue ones Note the client names and amounts Switch to your AI tool Type out all the details Ask what to do about it After (with mcp-freshbooks): "Which invoices are overdue? Draft follow-up messages for each client based on how late they are." Cla