The one Claude setting most founders never touch

Yesterday I told you about Claude Projects and context files.

Today: the one setting inside Projects that most people skip entirely — and why skipping it is costing them an hour a week.

Custom instructions vs. context files — what's the difference?

A context file (what I covered yesterday) tells Claude who you are. Custom instructions tell Claude how to behave every single time.

They're not the same thing. You need both.

Here's what I have in my custom instructions field right now:

- Always respond in plain text. No markdown unless I ask.
- Lead with the answer. Explain after.
- If you're uncertain, say so before I have to ask.
- Never summarize what I just said back to me.
- When I give you a task, tell me what's missing before you start.

Five rules. That's it. But every conversation now runs on those rails without me having to say it each time.

Why this matters at the solo founder stage:

You're the only person prompting your AI. Every minute you spend re-correcting output format is a minute you're not building. Custom instructions compress that friction to zero.

How to set it up:

Claude Pro → Your Project → Edit Project → Custom Instructions. Paste your rules. Save. Done.

Mine took 8 minutes to write. I've saved more than that every single day since.

The best version of this is one you write yourself — based on what you keep having to re-say. If you've corrected the same AI behavior more than twice, it belongs in your custom instructions.

Start there.

— Mira

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