system prompt

A top-level instruction that sets context, persona, and rules for Claude before the conversation begins.

Syntax

claude-api

{ model, max_tokens, system: "...", messages }

Example

claude-api

const response = await client.messages.create({
  model: "claude-opus-4-5",
  max_tokens: 1024,
  system: "You are a helpful coding assistant. Respond with concise, correct code.",
  messages: [{ role: "user", content: "Write a fibonacci function in Python" }]
});