Sandboxed Code Evaluation for AI-Generated Outputs — How I Built SafeCode Arena

The Problem: Candidate Code Without Trust You're using Cursor, Claude Code, or GitHub Copilot. The AI gives you three implementation options for the same feature. AI: "Here are three approaches: A) Quick but uses unsafe B) Slower but memory-safe C) Balanced tradeoffs" You: "Which one should I ship?" AI: "It depends..." That "it depends" is where responsibility falls through the cracks. Tests tell you if code compiles and passes specs. But they don't tell you about security, performance, maintainability, or resource limits — all at once. You end up making the call by gut feel. This essay is about building a system that doesn't let that happen. The Solution: Multi-Axis Scoring I built SafeCode Arena — an automated verifier that evaluates code candidates across five axes simultaneously, scores each, and surfaces the tradeoffs. The Five Axes Axis Weight Computation Correctness 50% compile (40%) + tests (40%) + property tests (20%) Security 20% unsafe heuristics (50%) + clippy warnings (50%) Performance 15% relative compile+test time across candidates Maintainability 10% function-length heuristics (60%) + clippy (40%) Resource Usage 5% pass/fail of sandboxed Wasm execution Why These Five? Correctness dominates — code that doesn't work is valueless, so it's 50% Security is explicit — unsafe compiles fine, but you need to detect it yourself Performance and maintainability matter equally — a fast mess vs. a slow masterpiece aren't comparable Resource limits are real — a 100-point algorithm that consumes 2GB is a fail in production Example Scorecard Candidate A: 85 points ├─ correctness: 100 (all tests pass) ├─ security: 60 (2 unsafe blocks flagged) ├─ performance: 70 (10% slower than B) ├─ maintainability: 85 (avg function 25 lines) └─ resource_usage: 80 (Wasm sandbox: 512MB, OK) Candidate B: 92 points ✓ Recommended ├─ correctness: 95 (1 edge case warning) ├─ security: 95 (no unsafe) ├─ performance: 95 (fastest) ├─ maintainability: 88 (avg function 20 lines) └─ resource_usa