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Original: Simon Willison · 13/03/2026

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Summary

Simon Willison shares his experience of building custom accounting software that meets his specific needs, highlighting its features and efficiency.

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Key Insights

“It’s a big mess, and no off-the-shelf accounting software does what I need.” — Introduction to the challenges faced with existing accounting software.
“It feels like bushwhacking with a lightsaber.” — Describing the intuitive and powerful nature of the custom software.
“It learns as I categorize expenses and categorizes automatically going forward.” — Highlighting the software’s learning capabilities and automation.

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Topics

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Full Article

13th March 2026 Simply put: It’s a big mess, and no off-the-shelf accounting software does what I need. So after years of pain, I finally sat down last week and started to build my own. It took me about five days. I am now using the best piece of accounting software I’ve ever used. It’s blazing fast. Entirely local. Handles multiple currencies and pulls daily (historical) conversion rates. It’s able to ingest any CSV I throw at it and represent it in my dashboard as needed. It knows US and Japan tax requirements, and formats my expenses and medical bills appropriately for my accountants. I feed it past returns to learn from. I dump 1099s and K1s and PDFs from hospitals into it, and it categorizes and organizes and packages them all as needed. It reconciles international wire transfers, taking into account small variations in FX rates and time for the transfers to complete. It learns as I categorize expenses and categorizes automatically going forward. It’s easy to do spot checks on data. If I find an anomaly, I can talk directly to Claude and have us brainstorm a batched solution, often saving me from having to manually modify hundreds of entries. And often resulting in a new, small, feature tweak. The software feels organic and pliable in a form perfectly shaped to my hand, able to conform to any hunk of data I throw at it. It feels like bushwhacking with a lightsaber. — Craig Mod, Software Bonkers

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Originally published at https://simonwillison.net/2026/Mar/13/craig-mod/#atom-everything.