Custom Instructions: Teaching Claude How You Work

The Memory Problem (and How to Solve It)

Claude does not remember you between conversations. Every new conversation starts from zero. This is by design — privacy and isolation between sessions. But it means that if you rely on Claude regularly, you are constantly re-explaining who you are, what you do, and how you like things done.

Custom instructions solve this. Write them once, and Claude applies them automatically to every conversation in that context. The difference between using Claude with good custom instructions and without them is dramatic — it is the difference between a knowledgeable colleague who knows your work and a stranger who needs to be briefed from scratch every time.

Two Types of Custom Instructions

Claude.ai has two places to set custom instructions:

• Global instructions — Apply to every conversation, everywhere in Claude.ai. Set these in Settings → Profile → Custom Instructions. These should cover universal preferences that apply to all your work: your name, your primary language, and your baseline communication preferences.
• Project instructions — Apply only to conversations in a specific Project. These should be task-specific: your role in this project, the audience you're writing for, the constraints, and the context.

Project instructions override global instructions when there is a conflict. Use global instructions for universal preferences, Project instructions for context-specific behavior.

Writing Global Instructions

Global instructions should be short — two to five sentences. Cover only what applies to every possible task you would use Claude for:

My name is Sarah. I'm a product manager at a software company. Always use US English spelling. Keep responses direct and concise — avoid long preambles before answering. If you're uncertain about something, say so rather than guessing.

Notice what this does NOT include: no mention of tone for a specific project, no mention of technical constraints, no mention of audience. Those belong in Project instructions.

Writing Project Instructions

Project instructions can be longer and more specific. Structure them in three sections:

• Context — What is this Project for? What is your role in it? Who is the intended audience for any output?
• Preferences — How should Claude write and respond? Tone, format, length, vocabulary, what to emphasize.
• Constraints — What should Claude always do or never do in this Project?

CONTEXT: This project is for drafting blog posts and email newsletters for a B2B SaaS company that sells project management software to professional services firms. Our audience is operations directors and project managers at companies with 50–500 employees. PREFERENCES: Write in a confident, direct tone — no hedging. Use short paragraphs (2–3 sentences max). Lead with the key point before explaining it. Use the Oxford comma. Avoid jargon. CONSTRAINTS: Never use the words "leverage," "synergy," "seamless," or "robust." Do not add filler sentences that pad length without adding value. Always end with a clear call to action.

Instructions for Different Use Cases

Some starting templates:

• For writing help: Describe your target reader, preferred tone, sentence length guidelines, and vocabulary restrictions
• For coding assistance: Specify your language, frameworks, coding style preferences, and whether you want explanations with the code
• For research: Describe your expertise level, the depth of analysis you want, and whether to cite sources or summarize without citations
• For brainstorming: Tell Claude how many ideas to generate, whether to evaluate them or just list them, and what constraints apply

Try This Now

Write custom instructions for one Project you would actually use. Open Claude.ai, create a new Project, and write instructions that cover: your role, the audience for your output, your tone preference, and at least two constraints. Then start a conversation in that Project without any additional context — just ask a question related to the project's purpose. Notice how Claude responds differently than it would in a blank conversation.