Diagnose Node.js CommonJS vs ESM Errors with Claude: A Copy-Paste Prompt Kit (ERR_REQUIRE_ESM, ERR_MODULE_NOT_FOUND)

By the end of this article you'll have a small Node.js script that pipes a module-resolution error ( ERR_REQUIRE_ESM , ERR_MODULE_NOT_FOUND , Cannot use import statement outside a module ) plus the surrounding config into Claude and gets back a specific fix — not a Stack Overflow lecture. You'll also have four hardened prompts you can paste straight into claude.ai, and a script that auto-detects whether your project is CJS or ESM before you even ask. Everything below runs on Node 18+. Why "just use ESM" doesn't fix the CommonJS/ESM ERR_REQUIRE_ESM error The reason these errors waste so much time is that the failing line is almost never where the problem lives. You see this: Error [ERR_REQUIRE_ESM]: require() of ES Module /app/node_modules/node-fetch/src/index.js from /app/server.js not supported. and your instinct is to edit server.js . But the actual decision is made by four things you can't see from the traceback: the "type" field in your package.json , the "type" (or "exports" map) in the dependency's package.json , your file extension ( .js vs .mjs vs .cjs ), and — if you use TypeScript — the module and moduleResolution fields in tsconfig.json . node-fetch v3 went ESM-only; that's why require('node-fetch') blows up while v2 was fine. The traceback tells you none of that. This is exactly the shape of problem an LLM is good at: lots of small context scattered across files, one correct answer, and a human who keeps pattern-matching on the wrong line. The trick is to feed Claude the config alongside the error, not the error alone. A prompt that only gets the stack trace will confidently tell you to "convert your project to ESM," which is often the most destructive possible fix. Prompt 1 for Claude: force a root-cause classification before any code The failure mode of asking an AI to "fix my module error" is that it jumps to a rewrite. The fix is to make it classify first. Paste this into claude.ai, filling the three blocks: You are debugging a Node.js module resolut