The Job Description Test
Here's a practical test you can apply to any agent identity you build, yours or someone else's.
Read the identity out loud. Then ask: could I replace this with a one-line job description and get essentially the same behavior?
"You are a customer support agent. Be helpful, accurate, and polite."
If that one-line description would produce output that's 90% similar to what the full identity produces, the identity isn't doing enough work. A well-designed identity produces behavior that a job description cannot replicate, because the identity shapes the agent's judgment, priorities, and reasoning patterns in ways that a job description cannot specify.
The inverse test is also useful. Take your full identity and try to compress it into a one-line job description. What do you lose? The things you lose are the things the identity is actually contributing. If you lose nothing, the identity is decorative. If you lose the agent's distinctive way of thinking, the identity is functional.