xllify

Excel runs more business logic than any other piece of software. The problem is what happens when you need to go beyond what's built in. VBA is a single-threaded antique. C++ XLLs require specialist knowledge and a painful build toolchain. Python offerings are mature but carry the overhead that comes with Python. Office.js runs in a browser sandbox and can be tricky to deploy and "get right" with a slightly haphazard developer experience, and doesn't always perform well.

xllify takes a different approach. Write functions in Lua, and xllify compiles them to bytecode and bundles everything into a self-contained XLL (here's some more in-depth notes on xllify add-in security) or Office.js add-in. No runtime to install, no environment to manage. It ships as a single file and works on Windows, Mac, and the web.

The company

xllify is built and maintained by Lexvica Limited, a software consultancy based near Newcastle, UK, founded in 2025. The idea had been brewing for a while, born out of time spent working at a trading firm and being genuinely stunned by how much of the world runs on Excel. We also offer consulting to build your add-ins, data engineering, data streaming, and Excel-adjacent tooling. Meet the team.

How it works

xllify is a platform for creating custom Excel functions. Describe what you need in a prompt, or write code directly. Work in the browser, in Excel via the xllify Assistant add-in, or locally with the CLI.

xllify prioritises verified, tested implementations from the standard library (open source) before generating new code. The standard library includes native C++ primitives for performance-critical operations, available to every function, including those generated by AI. The runtime is available for Windows, Mac and Web.

Accelerated on Windows: In addition to cross-platform web add-ins, xllify can build native XLL add-ins for Windows. XLLs run in-process with Excel with multi-threaded recalculation, self-contained in a single file with no web server or internet connection required.

Function code runs in a sandboxed VM with no access to the network or file system, so XLLs built with xllify cannot be used as an attack vector. Both runtimes execute the same bytecode, so functions work identically everywhere. XLL builds are available to all users; free tier builds expire after thirty days.

Remote build service

xllify compiles and packages your add-ins in the cloud. Write your functions in the browser or in Excel, and xllify produces a ready-to-use add-in in seconds. This applies to both Office Add-ins and native XLL builds for Windows. Local tooling is available if you prefer to work that way; builds always go through the remote service. Fair use applies.