Designing an MCP server for a 240-operation legacy API (QuickBooks Desktop)

Description and use

<p><em>Disclosure: I built LedgerCrossing, the product this article is about. It's paid software, so I'm biased. The design problems are real either way, and I hope they're useful if you're wrapping a big legacy API in MCP.</em></p> <p>QuickBooks Desktop is the Windows version of QuickBooks that a lot of businesses still run on Pro, Premier or Enterprise. It has no cloud API. The only way in is qbXML, an XML request format, through a COM interface on the machine where QuickBooks runs. That's why most QuickBooks MCP servers are for QuickBooks Online, which has a cloud API to wrap.</p> <p>I buil

Problem

<p><em>Disclosure: I built LedgerCrossing, the product this article is about. It's paid software, so I'm biased. The design problems are real either way, and I hope they're useful if you're wrapping a big legacy API in MCP.</em></p> <p>QuickBooks Desktop is the Windows version of QuickBooks that a lot of businesses still run on Pro, Premier or Enterprise. It has no cloud API. The only way in is qbXML, an XML request format, through a COM interface on the machine where QuickBooks runs. That's why most QuickBooks MCP servers are for QuickBooks Online, which has a cloud API to wrap.</p> <p>I buil

Outcome

<p><em>Disclosure: I built LedgerCrossing, the product this article is about. It's paid software, so I'm biased. The design problems are real either way, and I hope they're useful if you're wrapping a big legacy API in MCP.</em></p> <p>QuickBooks Desktop is the Windows version of QuickBooks that a lot of businesses still run on Pro, Premier or Enterprise. It has no cloud API. The only way in is qbXML, an XML request format, through a COM interface on the machine where QuickBooks runs. That's why most QuickBooks MCP servers are for QuickBooks Online, which has a cloud API to wrap.</p> <p>I buil

Evidence

Designing an MCP server for a 240-operation legacy API (QuickBooks Desktop)

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