Mistakes AI Coding Agents Make

I use Codex to write tools while I walk. Here are merged PRs:

• Add editable system prompt
• Standardize toast notifications
• Persist form fields
• Fix SVG handling in page2md
• Add Google Tasks exporter
• Add Markdown table to CSV tool
• Replace simple alerts with toasts
• Add CSV joiner tool
• Add SpeakMD tool

This added technical debt. I spent four hours fixing the AI generated tests and code.

What mistakes did it make?

1. Inconsistency. It flips between execCommand("copy") and clipboard.writeText(). It wavers on timeouts (50 ms vs 100 ms). It doesn’t always run/fix test cases.
2. Missed edge cases. I switched <div> to <form>. My earlier code didn’t have a type="button", so clicks reloaded the page. It missed that. It also left scripts as plain <script> instead of <script type="module"> which was required.
3. Limited experimentation. My failed with a HTTP 404 because the common/ directory wasn’t served. I added console.logs to find this. Also, happy-dom won’t handle multiple exports instead of a single export { ... }. I wrote code to verify this. Coding agents didn’t run such experiments.

What can we do about it?

Three things could have helped me:

1. Detailed coding rules. E.g. always run test cases and fix until they pass. Only use ESM. Always import from CDN via JSDelivr. That sort of thing.
2. 100% test coverage. Ideally 100% of code and all usage scenarios.
3. Log everything. My tests got a HTTP 404 because I was not serving the common/ directory. LLMs couldn’t figure this out because it was not logged. Logging everything helps humans and LLMs debug.
4. Wait. LLMs and coding agents keep improving. A few months down the line, they’ll run more experiments themselves.

Was AI coding worth the effort? Here, yes. The tools worked. Codex saved me 90% effort. My code quality obsession reduced savings to ~70%. Still huge.