Yesterday a Reddit user named Pitiful_Bat8731 dropped something small and genuinely clever into r/PromptEngineering: a Codex skill called $null. Here’s the twist. It doesn’t make Codex smarter. It makes Codex quieter.
The idea: you type $null, and Codex switches into a mode where it just replies “Received” while you think out loud. No suggestions, no “have you considered,” no filling in the blanks you haven’t decided yet. You talk until you’re done, then say “null off” and Codex goes back to being Codex.
Here’s why that’s worth noticing. We spend most of our energy getting AI to talk more. This guy built a skill whose entire job is getting it to talk less, on purpose, until you tell it to stop being quiet.
How it works, step by step:
- 🧠 Load the skill in your Codex setup (it’s MIT licensed, repo’s on GitHub)
- 💬 Type $null to switch into listening mode
- 🗣️ Think out loud, dictate, ramble, whatever gets the idea out of your head
- 🔚 Say “null off” when you’re ready for actual input again
Pro tip: the skill sets allow_implicit_invocation: false, so Codex never slides into this mode on its own. You have to ask for it. That’s the right default. You don’t want your assistant deciding when it gets to stop talking.
One honest caveat straight from the builder: this was tested lightly. Nine of twenty behavioral cases got a single run against an earlier version, no measured success rate, no proof it actually improves your thinking. He used it to dictate an article and liked the result. That’s one data point, not a study.
Still worth trying if you’ve ever opened a chat with an AI and had it finish your sentence before you’d figured out what you meant. Grab the skill, steal the pattern for your own tools, and tell us what “null off” surfaces for you. ⚓
Frequently Asked Questions
Q: How is $null different from just telling the model “don’t respond yet”?
Great question , functionally they can be similar, but the explicit on/off ritual creates a psychological boundary that changes how you interact. The handshake protocol (model says “Received” and waits) reinforces that you’re in thinking mode, not response mode. Some users find this intentionality shifts their problem-solving approach, though the benefit is subjective rather than measured.
Q: Does $null help when you need to iterate mid-workflow?
Yes , by enforcing a “wait for my question” pattern, it naturally supports step-by-step iteration instead of the model dumping all 10 steps at once. If something unexpected happens at step 2, you ask about it directly, and the model responds to that specific problem rather than re-running pre-planned steps.
Q: What’s the difference between the main skill and the companion subagent prompt?
The main skill keeps you thinking within your conversation thread. The companion prompt spawns a fresh subagent with only the text you select, completely isolating your thinking from your main context. Use the skill for focused iteration within a project, and the subagent for a completely clean slate.
Q: Is there proof that $null actually improves thinking?
The author tested it on 20 behavioral cases and found no measured success rate or hard evidence. However, their subjective experience was that the ritual of thinking out loud (before asking for input) forced deeper engagement with ideas , worth experimenting with, but not a guaranteed win.
$null: a skill for thinking out loud before asking Codex for input
by u/Pitiful_Bat8731 in PromptEngineering