Designing APIs other developers love

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The problem

Most performance issues come from doing too much work on every request. Measure first, then fix the slowest part.

💡 Tip: profile in production-like conditions — your laptop lies.

The solution

Here is the core idea in a few lines of JavaScript:

// consistent errors make clients simple
res.status(422).json({
  error: 'validation_failed',
  fields: { email: 'Email is already taken' }
});

⚠️ Warning: cache invalidation is the hard part — always set a TTL.

Results

• Response time dropped from 820 ms to 140 ms.
• Database load fell by 70%.
• No new infrastructure needed.

✅ Best practice: add a regression test so the slowdown never comes back.