ChatGPT system instructions

ChatGPT is strongest when the answer has a shape you can name in advance: JSON, a table, a function signature, a sequence of tool calls. Custom instructions and project files persist your rules across a conversation, so most of what people paste into every message belongs there instead. Long inputs are handled well, but the model follows the most recent instruction more eagerly than the first one, so keep the binding rules near the end of a long prompt.