vibe porting
In plain wordsUsing AI coding agents to translate a whole software project into another programming language, usually checking the result against the original project's tests.
The use of coding agentscoding agent, n.: An AI agent that writes and fixes software by itself: it reads a codebase, edits files, runs commands and tests, and keeps working until a feature is built or a bug is fixed. to port an existing codebase from one programming language to another, or to reimplement it from scratch, typically using the original project's test suite both as the specification and as an automatic check of the result. Ports that once took months were reported in hours: in December 2025 Simon Willison ported an HTML5 parser from Python to JavaScript in about four and a half hours. The practice raised legal questions in 2026 about whether agent-written reimplementations escape the original's license. When the maintainer of the Python library chardet released an AI-assisted 'ground-up' rewrite under the permissive MIT license in March 2026, its original author objected that LGPL code could not be relicensed this way, reviving debate over what counts as a clean-room implementation when the model may have been trained on the original.
We vibe-ported the validator to Rust over a weekend; the old test suite did most of the reviewing.
Origin
Formed on the model of vibe codingvibe coding, n.: Programming by conversation: you ask an AI for what you want, try out what it produces and ask again until it works, trusting the code without really reading it. and used by Simon Willison from December 2025 as a recurring blog category; Anil Madhavapeddy used the related 'vibespiling' (vibe transpiling) the same month. Usage is still largely confined to developer blogs.
Usage note
Using reimplementation to shed copyleft obligations has been dubbed 'license washing'. A co-author of the GPLv3 and LGPLv3 saw no clear basis for requiring the chardet rewrite to stay under the LGPL, which shows how unsettled the question is.
Related
- vibe codingvibe coding, n.: Programming by conversation: you ask an AI for what you want, try out what it produces and ask again until it works, trusting the code without really reading it.
- agentic codingagentic coding, n.: Writing software by directing AI agents that plan, edit and test code themselves, with the human acting more as a reviewer and manager than as the person typing every line.
- coding agentcoding agent, n.: An AI agent that writes and fixes software by itself: it reads a codebase, edits files, runs commands and tests, and keeps working until a feature is built or a bug is fixed.
- AI copyright litigationAI copyright litigation, n.: The many lawsuits in which authors, artists, news organizations, record labels and others accuse AI companies of copying their work without permission to build or run AI models.
- fair use and AI trainingfair use and AI training, phr.: The unsettled US legal question of whether AI companies may copy books, articles, pictures and music to train their models without permission, under the rule that allows some unlicensed uses of copyrighted work.
- dark factorydark factory, n.: A way of building software in which AI agents write, test and ship all the code and no human writes or reads it, like a factory run with the lights off.
Sources
- Willison, S. (2026). Can coding agents relicense open source through a "clean room" implementation of code? Simon Willison's Weblog, 5 March 2026. simonwillison.net/2026/Mar/5/chardet
- Willison, S. (2025). I ported JustHTML from Python to JavaScript with Codex CLI and GPT-5.2 in 4.5 hours. Simon Willison's Weblog, 15 December 2025. simonwillison.net/2025/Dec/15/porting-justhtml
- Willison, S. Posts tagged vibe-porting. Simon Willison's Weblog. simonwillison.net/tags/vibe-porting