You've used three pre-configured analyst agents already — one for the spreadsheet, one for the strategy doc, one for benchmarks. Same Claude model behind each. What made them act like different specialists was the system prompt — the persona.

Now you write your own.

A Persona Has Four Parts

A good system prompt isn't a paragraph of vibes. It's a small set of named pieces, each doing a specific job:

Write all four and the agent behaves consistently. Skip one and it drifts.

What Drifts When You Skip a Part

• No identity — generic, hedging answers like "it depends on context";
• No tool guidance — the agent forgets to call the tool and guesses;
• No output format — every response shaped differently, no consistency;
• No constraint — the agent invents numbers when the data is missing.

The next two labs make you write all four. First with one tool, then with three.

Takeaway: A persona is a contract. Specify it once, get the same agent every time.