Unified TypeScript library for streaming, structured outputs, and agent loops across AI providers
Full evaluationGlossary · Updated Sep 2, 2026
System prompt
Hidden instructions set by a product or developer that define an assistant's role, rules, tone, and constraints.
Definition
A system prompt sits above user messages and shapes every response: what the assistant can discuss, how it formats answers, which tools it may use, and how it should refuse. Products expose parts of this through custom instructions, personas, or agent settings. Well-designed system prompts are a major part of product quality.
Why it matters when choosing a tool
When a tool lets you set custom instructions or build agents, you are effectively editing the system prompt, which is where consistency and safety live.
Where you will meet it
AI Agent & Chatbot Builders, AI Customer Support, AI Assistants
Related terms
Tools where this matters
Reviewed products in the related categories
Prototyping environment and developer API platform for Google's Gemini models
Full evaluation
A source-available workflow automation platform with native AI agent nodes, self-hostable or cloud.
Full evaluation
An AI support agent inside Intercom that resolves customer conversations from your help content and hands off to people.
Full evaluation
AI agents, agent copilots, and automation built into the Zendesk support suite.
Full evaluation
A visual platform for designing, testing, and deploying AI agents for support and conversational products.
Full evaluation