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.
User preferences
In your Claude account settings, you can define custom instructions that apply to every new conversation. Claude reads them before you send your first message.
| Setting | What you control |
|---|---|
| Tone | Formal, casual, friendly, technical, or encouraging |
| Format | Paragraphs, bullet points, tables, or step-by-step |
| Length | Concise summaries or detailed explanations |
These preferences apply to every new conversation
How system-level instructions work
Custom instructions are system-level — they sit behind your messages and guide Claude before it generates a reply. You do not 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:
Claude combines all three layers. More specific instructions (chat, then project, then account) take priority when they conflict.
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
If full custom instructions are more than you need, Claude offers a style customization feature — preset communication styles you can toggle without crafting detailed prompts.
Pick combinations like “Professional + Concise” or “Friendly + Detailed” and Claude adjusts how it writes.
• Revenue grew 12% quarter-over-quarter
• Customer retention improved to 94%
• Operating costs remained flat
You:
“Explain how APIs work.”
Claude:
An API (Application Programming Interface) is a set of rules that lets different software applications communicate. When you use a weather app, it calls a weather API to fetch data.
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
Personas
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…”
| Persona | Instructions | Example use |
|---|---|---|
| Patient Tutor | “You are a patient tutor. Explain concepts simply, use analogies, and check understanding before moving on.” | Learning a new programming language or maths topic |
| Copy Editor | “You are a sharp copy editor. Fix grammar, tighten prose, and flag unclear sentences. Preserve the author's voice.” | Editing blog posts, emails, or essays |
| Devil's Advocate | “You challenge my ideas constructively. Present counterarguments and weaknesses I may have missed.” | Reviewing a business plan or product decision |
Writing effective instructions
| Quality | Example |
|---|---|
| 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.” |
Before you continue
- Set tone, format, and length once in Profile → Custom instructions.
- Instructions layer: account, then project, then per-message prompt.
- Style customization offers quick presets without full instructions.
- Personas set a role — save them in Projects for recurring use.
- Next lesson: Conversations and History.
What's Next
Conversations & History — find old chats, point back to earlier messages, and know when a thread gets too long.