One-sentence description of what this project is, for someone who has never heard of it before.
What problem was this solving, and for whom? Who asked for it (or why did you decide to build it yourself)? What constraints were you working under — time, budget, team size, existing systems? Ground the reader in the situation before you get to what you did.
How did you plan it? What were the key early decisions, and what alternatives did you consider and reject? This is the section that shows how you think, not just what you built — walk through the reasoning, not only the output.
Be honest here. What worked as planned? What didn't? Where did you have to pivot, and what triggered the change? This is usually the most credible part of a case study — it shows judgment under real conditions, not just a highlight reel.
What actually resulted — usage numbers, feedback, what shipped, what you'd call a win. If there isn't a metric, describe the qualitative outcome honestly (e.g. "used by X people," "shelved after Y, and here's what I took from that").
One or two honest reflections. This is the section that tells a hiring manager you learn from your own work — arguably more persuasive than the win itself.