Claude ChatLesson 7

Custom Instructions & Personas

You do not have to repeat your preferences in every message. Custom instructions set default tone, format, and length. Personas set a fixed role for a type of work.

Setting user preferences

In your Claude account settings, you can define custom instructions that apply to every new conversation. They work as defaults — Claude reads them before you send your first message.

🎙️
Tone

Formal, casual, friendly, technical, or encouraging

📐
Format

Paragraphs, bullet points, tables, or step-by-step

📏
Length

Concise summaries or detailed explanations

claude.ai → Settings → Profile
Custom instructions
These preferences apply to every new conversation
What should Claude know about you?
I'm a software developer working on educational apps. I prefer concise, practical answers.
How should Claude respond?
Use a professional but friendly tone. Keep answers under 300 words unless I ask for detail. Use bullet points for lists.
Tone
Professional
Format
Bullet points
Length
Concise
Save preferences
User preferences in Profile settings — tone, format, and length apply to all conversations
Where to find it: Go to Settings → Profile → Custom instructions at claude.ai. Fill in what Claude should know about you and how it should respond. Changes apply to new chats immediately.

How system-level instructions work

Custom instructions are system-level — they sit behind your messages and guide Claude before it generates a reply. You never see them in the chat, but they influence every response.

Instructions can exist at three levels. Claude combines them, with more specific levels taking priority:

How instructions layer — each level shapes Claude's behavior
1
Account
User custom instructions
Your global tone, format, and background — applies everywhere
2
Project
Project instructions
Domain-specific rules for all chats in a project
3
Chat
Message prompt
Your specific request in this conversation
Claude combines all three layers. More specific instructions (chat > project > account) take priority when they conflict.
System-level instructions stack — account, project, and per-message prompts work together

What system instructions can control

✓Response tone and voice
✓Output format and structure
✓Default answer length
✓Role or expertise (persona)
✓Topics to avoid or emphasize
✓Language and vocabulary level

Style customization feature

If full custom instructions are more than you need, Claude offers a style customization feature — preset communication styles you can toggle on without crafting detailed prompts.

Pick combinations like "Professional + Concise" or "Friendly + Detailed" and Claude adjusts how it writes. You can change styles at any time from your profile settings.

Style customization
Choose how Claude communicates with you
Communication style
FormalProfessionalFriendlyConciseDetailed
Preview
Here are the three key points from your report:
• Revenue grew 12% quarter-over-quarter
• Customer retention improved to 94%
• Operating costs remained flat
Let me know if you need a deeper breakdown.
Style customization lets you pick communication presets without writing full instructions
Style: Default
You:
"Explain how APIs work."
Claude:
An API (Application Programming Interface) is a set of rules that lets different software applications communicate with each other. When you use a weather app, it calls a weather API to fetch data. The API defines what requests you can make and what responses you will get back.
Style: Concise & direct
You:
"Explain how APIs work."
Claude:
• An API is a contract between two programs • One app sends a request; the other returns data • Example: a weather app calls a weather API for forecasts
Same question, different style — custom instructions change how Claude structures its answer

Personas — role-based instructions

A persona is a set of instructions that sets a fixed role for Claude. Use personas in custom instructions, project settings, or in a message: "You are a…"

👨‍🏫
Patient Tutor
Instructions

"You are a patient tutor. Explain concepts simply, use analogies, and check understanding before moving on."

Example use

Learning a new programming language or maths topic

✍️
Copy Editor
Instructions

"You are a sharp copy editor. Fix grammar, tighten prose, and flag unclear sentences. Preserve the author's voice."

Example use

Editing blog posts, emails, or essays

⚖️
Devil's Advocate
Instructions

"You challenge my ideas constructively. Present counterarguments and weaknesses I may have missed."

Example use

Reviewing a business plan or product decision from the opposing side

Tip: For recurring personas, save them as a Project's custom instructions instead of typing "You are a…" every time. Switch projects to change personas.

Writing effective instructions

✓
Specific"Keep answers under 200 words. Use bullet points for lists."
✓
Specific"I am a beginner programmer. Avoid jargon and explain terms when you use them."
✗
Too vague"Be helpful."
✗
Too vague"Always be perfect and never make mistakes."
Summary:
  • Set tone, format, and length once in Profile → Custom instructions.
  • System-level instructions layer: account → project → per-message prompt.
  • Style customization offers quick presets without writing full instructions.
  • Personas set a role for Claude — save them in Projects for recurring use.

What's Next

Conversations & History — find old chats, point back to earlier messages, and know when a thread gets too long.