Same agent. Same prompts. One skill apart.

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I gave Codex (GPT-6.1 Sol) the same brief twice: a configurable business site with a 3D hero. One run had Google's Modern Web Guidance installed, the other didn't. These are the two finished builds, untouched. Add ?mode=config or use the editor buttons to try the site editor.

Without MWGVeyrspan Thermal, the build without the skill

Editor is one long block at the top of the page
Accepted a script from any address in config.json
1 h 4 min of agent time

Open the site Open the editor

With MWGRillfold Acoustics, the build with the skill

Editor is a docked side panel with grouped controls
Only accepts scripts from HTTPS addresses
2 h 3 min of agent time, including a self-check it asked for

Open the site Open the editor