Simon Willison’s Weblog

The boring yet crucial secret behind good system prompts is test-driven development. You don't write down a system prompt and find ways to test it. You write down tests and find a system prompt that passes them.

For system prompt (SP) development you:

• Write a test set of messages where the model fails, i.e. where the default behavior isn't what you want
• Find an SP that causes those tests to pass
• Find messages the SP is missaplied to and fix the SP
• Expand your test set & repeat

— Amanda Askell