Prompts: What You Type Right Now
A prompt is the message you type at the start of a conversation or during a conversation to give Claude a specific task. "Write a 600-word blog post about [topic]." "Review this email and suggest improvements to the CTA." "Summarize this document with a focus on the key action items."
Prompts are per-conversation and per-task. They instruct Claude on what to do right now. Each prompt produces output for the specific request made in that prompt.
System Prompts: Standing Behavioral Rules
A system prompt is a set of instructions that applies to every conversation -- not just the current one. It defines Claude's role, output format preferences, behavioral constraints, and communication style. "Always respond in prose, never bullet points unless asked." "Act as my content strategist." "Flag any claims requiring data verification."
The key distinction: a prompt tells Claude what to do right now. A system prompt tells Claude how to behave always. Prompts are inputs. System prompts are configuration.
Where They Live in Claude Projects
Both can live in Claude Projects as uploaded documents. A system prompt is typically a document labeled "System Instructions" or "Behavior Rules" uploaded to the project. Claude reads it at the start of every conversation. Your regular prompts are what you type in each conversation on top of that persistent system context.
When to Use Each
Use prompts for task-specific instructions that only apply to the current request. Use system prompts for behavioral rules that should apply consistently across all conversations -- response format, role definition, constraints, flags.