Stop Optimizing Your Code. Optimize Your Interfaces.

The OpenUI team rewrote their DSL parser from Rust/WASM to plain TypeScript. It got 2.2 to 4.6 times faster . Not because TypeScript is faster than Rust. It isn't. Because the boundary between WASM and JavaScript was the actual bottleneck — copying strings into WASM memory, serializing with serde_json, copying JSON back to the JS heap, then parsing it again with V8. The Rust parsing itself was never the slow part. They tried optimizing the boundary with serde-wasm-bindgen (fine-grained interop instead of bulk JSON). It was 30% slower . Less frequent, larger transfers beat more frequent, smaller ones. This story contains a principle that applies far beyond WASM: the bottleneck in your system is almost never the code inside a module. It's the interface between modules. This Isn't Just About Performance Here's where it gets interesting. The same principle applies to how we think. The METR study (2025, updated 2026) measured experienced developers using AI coding tools on real tasks. The r