Codex Tool Reference vs Vellum
Both are listed under Developer Tools. Here is how they differ on the facts we track.
Codex Tool Reference
codex-tool-reference.simonw.chatgpt.site
Vellum
vellum.ai
| Feature | Codex Tool Reference | Vellum |
|---|---|---|
| What it is | A complete reference to the tools and full skill definitions available in this Codex Work session. | An assistant that knows you deeply, evolves alongside you, and belongs to no one else. |
| Pricing | paid | open source |
| Categories | Developer Tools, Productivity | Productivity, Developer Tools |
| Platforms | Web, iOS, CLI | macOS, iOS, CLI |
| Upvotes | 0 | 1 |
| Last verified | 2026-09-10 | 2026-09-10 |