Simon Willison Tests smolmachines and smolvm as a Sandbox for Untrusted Python and JavaScript
On 19 August 2026, Simon Willison documented his experiment tasking Claude Fable 5 within Claude Code for web to evaluate smolmachines.com as a secure sandbox for untrusted Python and JavaScript. The goal was to enforce RAM/CPU limits, prevent infinite loops, block network access, and restrict filesystem access to designated files, enabling safe user-provided data transformations. The web environment couldn't run smol machines, so Claude installed smolvm and ran tests via a GitHub Actions runner. Willison called this a creative workaround and an example of Fable's proactive behavior. The post also mentioned a $10/month sponsorship for a monthly LLM digest.
Key facts
- Simon Willison posted on 19th August 2026.
- He tasked Claude Fable 5 running in Claude Code for web.
- The task was to test smolmachines.com as a sandbox.
- The sandbox targets untrusted Python and JavaScript code.
- Requirements included limiting RAM and CPU time and preventing 'while true' loops.
- Network access was to be blocked and filesystem access restricted to designated files.
- The goal was to execute user-provided tasks for data transformations.
- Claude Code for web couldn't run smol machines, so Claude installed smolvm and ran tests in a GitHub Actions runner.
Entities
Artists
- Simon Willison
Institutions
- Claude Code
- smolmachines
- smolvm
- GitHub Actions