AI coding · Advanced
System Prompt
Also called: System message, System instructions, Custom instructions
Underlying instructions given to the model before the conversation starts. They set its role, behavior, and rules, and usually take priority over normal messages.
In detail
A system prompt is like the handbook a new employee gets on day one. Before any specific task, they already know who they are, how to work, and what not to do. Tools like Cursor and Claude Code have built-in system prompts that tell the model it's a coding assistant, which tools it can use, and what format to reply in.
Regular users usually can't see or change a tool's built-in system prompt. The Rules File you write gets loaded into the context by the tool and works like a "supplement to the handbook." If you call a large model's API yourself to build a product feature, you'll need to write the system prompt yourself.
How the three differ: the System Prompt is the underlying setup. The Prompt is the specific task you send each time. The Rules File is a long-term, project-level agreement that the tool attaches automatically.
Developer infoTerm ID, DOM cues, match priority
- Term ID
ai-system-prompt- DOM selectors
- No DOM cues. This concept isn't detected directly on a page.
- Priority
- 1 · when several match at the same level, the higher priority wins
- Version
- v1 · updated Sep 29, 2026