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Custom Instructions & Styles

Beginner
What you'll learn
  • Tell custom instructions apart from styles — and know which one to reach for
  • Write a first set of standing instructions in three lines that are worth keeping
  • Understand the stacking order when four layers of instruction disagree
  • Avoid the two mistakes that make standing instructions worse than none

Tired of repeating "be concise" or "I'm a nurse, explain accordingly" every chat? Custom instructions and styles let you set your defaults once and have them apply everywhere.

Custom instructions = your personal system prompt​

Set standing facts and preferences — who you are, what you do, how you like answers — and Claude applies them across conversations. It's the consumer-app version of a system prompt (and the cousin of CLAUDE.md for developers).

Good things to include:

  • Context about you ("I run a small bakery"; "I code in Python").
  • Output preferences ("default to short bullet answers"; "always show your reasoning").
  • Hard rules ("never use emoji"; "metric units").
Guided walkthrough1 of 4
  1. Role, domain, and anything that changes the right answer — "I'm a district nurse in the UK" or "I write Python 3.12 services".

A starter set of custom instructions

I'm a district nurse in the UK. I read fast and act on summaries.

Default to short bullet answers with no preamble. Metric units. Flag anything
that is clinical guidance I should confirm against current NHS sources.

Never use emoji.

Styles = presentation presets​

Styles change tone/format (concise, formal, explanatory, etc.) and can be switched per conversation. Use a style when you want a different voice for this chat without rewriting your standing instructions.

How they stack​

More specific/later context tends to win when there's a conflict — so a Project's instructions or an explicit ask in your message can override your global defaults. Keep them consistent to avoid surprises.

Tips​

  • Keep instructions short and true — like CLAUDE.md, bloat and stale rules hurt.
  • Don't put secrets in custom instructions.
  • Revisit them occasionally as your needs change.
Four layers, four jobs
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1 / 5

Check yourself

0/3
  1. You want a formal tone for one conversation only, without touching your defaults. What do you use?
  2. Your account instructions say "always use bullets" but a Project's instructions ask for prose. What tends to happen in that Project?
  3. Which of these does NOT belong in custom instructions?
Key takeaways
  • Custom instructions are standing defaults; styles are a per-chat voice. Reach for the narrower one.
  • Three lines — who you are, your default output shape, one or two hard rules — beats a long rulebook.
  • Four layers feed each conversation: account instructions, style, Project instructions, this turn's message.
  • More specific or later context tends to win a conflict, so keep the layers consistent.
  • Never put secrets in standing instructions, and prune stale rules as your needs change.

Next​