We Rewrote JSONata with AI in a Day, Saved $500K/Year

Simon Willison’s Weblog Subscribe Sponsored by: WorkOS — Ready to sell to Enterprise clients? Build and ship securely with WorkOS. We Rewrote JSONata with AI in a Day, Saved $500K/Year. Bit of a hyperbolic framing but this looks like another case study of vibe porting, this time spinning up a new custom Go implementation of the JSONata JSON expression language - similar in focus to jq, and heavily associated with the Node-RED platform. As with other vibe-porting projects the key enabling factor was JSONata's existing test suite, which helped build the first working Go version in 7 hours and $400 of token spend. The Reco team then used a shadow deployment for a week to run the new and old versions in parallel to confirm the new implementation exactly matched the behavior of the old one. Posted 27th March 2026 at 12:35 am Recent articles Experimenting with Starlette 1.0 with Claude skills - 22nd March 2026 Profiling Hacker News users based on their comments - 21st March 2026 Thoughts on OpenAI acquiring Astral and uv/ruff/ty - 19th March 2026 This is a link post by Simon Willison, posted on 27th March 2026. go 51 json 146 ai 1934 generative-ai 1715 llms 1681 agentic-engineering 34 vibe-porting 7 Monthly briefing Sponsor me for $10/month and get a curated email digest of the month's most important LLM developments. Pay me to send you less! Sponsor & subscribe Disclosures Colophon © 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025 2026