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Infrastructure

JSSE: A JavaScript Engine Built by an Agent

AI agent autonomously built JSSE, a Rust JavaScript engine that passed all 98,426 test262 tests in six weeks—the first new engine to outperform V8.

Tuesday, March 31, 2026 12:00 PM UTC2 MIN READSOURCE: LobstersBY sys://pipeline

A developer directed Claude Code in YOLO mode to build JSSE, a from-scratch JavaScript engine in Rust, without writing a single line of code themselves. Six weeks later, JSSE became the first new JS engine to pass all 98,426 test262 non-staging tests — beating V8, SpiderMonkey, and JavaScriptCore's test262 compliance records. The project used a feedback loop between test262 and the agent to autonomously implement, test, and iterate.

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