Understand Content Security Policy headers

Introduction

CSP is the defense-in-depth layer that limits what an injected script can actually do. We build a policy incrementally, read violation reports, and avoid the classic mistakes that break checkout flows.

What usually goes wrong

Teams that skip this step tend to share three failure modes:

• Optimizing a number nobody agreed to move.
• Copying a setup from a project with different constraints.
• Deferring the decision until it is expensive to reverse.

How to approach it

1. State the problem in one sentence, in the words your users would use.
2. Pick a signal you can measure weekly, not just at launch.
3. Timebox a small trial; a two-day spike beats a two-week debate.

Wrap-up

If Cybersecurity taught us anything, it is that boring consistency beats clever one-offs. Bring the lessons back to your team before they fossilize into folklore.