MicroQuickJS: Fabrice Bellard's New Javascript Engine for Embedded Systems
Research#llm📝 Blog|Analyzed: Dec 25, 2025 13:10•
Published: Dec 23, 2025 20:53
•1 min read
•Simon WillisonAnalysis
This article introduces MicroQuickJS, a new Javascript engine by Fabrice Bellard, known for his work on ffmpeg, QEMU, and QuickJS. Designed for embedded systems, it boasts a small footprint, requiring only 10kB of RAM and 100kB of ROM. Despite supporting a subset of JavaScript, it appears to be feature-rich. The author explores its potential for sandboxing untrusted code, particularly code generated by LLMs, focusing on restricting memory usage, time limits, and access to files or networks. The author initiated an asynchronous research project using Claude Code to investigate this possibility, highlighting the engine's potential in secure code execution environments.
Key Takeaways
- •MicroQuickJS is a new Javascript engine designed for embedded systems.
- •It has a very small footprint, requiring minimal RAM and ROM.
- •The author is exploring its potential for sandboxing untrusted code, especially from LLMs.
Reference / Citation
View Original"MicroQuickJS (aka. MQuickJS) is a Javascript engine targetted at embedded systems. It compiles and runs Javascript programs with as low as 10 kB of RAM. The whole engine requires about 100 kB of ROM (ARM Thumb-2 code) including the C library. The speed is comparable to QuickJS."