Why it matters

Here is the practical punchline, and it shows up in nearly every source in this collection: investing in the harness usually beats tweaking the prompt.

If your agent keeps doing the wrong thing, your instinct is to rewrite the system prompt. Sometimes that helps. But the engineers who build these systems consistently find that the bigger wins come from better tool descriptions, better permission rules, better memory files, and better context management. The Snyk team that studied Cursor's security agents found the prompt driving a system that catches hundreds of real vulnerabilities was a mere fifteen lines. The prompt was simple precisely because the infrastructure underneath it (state tracking, deduplication, deployment, orchestration) was not. The harness was carrying the weight.

So if you want to build a capable agent, most of your effort is not going to be prompt wording. It is going to be plumbing. This guide is mostly about that plumbing.