---

name: api-response-optimization description: Optimizes API performance through payload reduction, caching strategies, and compression techniques. Use when improving API response times, reducing bandwidth usage, or implementing efficient caching.

API Response Optimization

Reduce payload sizes, implement caching, and enable compression for faster APIs.

Sparse Fieldsets

Copy// Allow clients to select fields: GET /users?fields=id,name,email
app.get('/users', async (req, res) => {
  const fields = req.query.fields?.split(',') || null;
  const users = await User.find({}, fields?.join(' '));
  res.json(users);
});

HTTP Caching Headers

Copyapp.get('/products/:id', async (req, res) => {
  const product = await Product.findById(req.params.id);
  const etag = crypto.createHash('md5').update(JSON.stringify(product)).digest('hex');

  if (req.headers['if-none-match'] === etag) {
    return res.status(304).end();
  }

  res.set({
    'Cache-Control': 'public, max-age=3600',
    'ETag': etag
  });
  res.json(product);
});

Response Compression

Copyconst compression = require('compression');

app.use(compression({
  filter: (req, res) => {
    if (req.headers['x-no-compression']) return false;
    return compression.filter(req, res);
  },
  level: 6  // Balance between speed and compression
}));

Performance Targets

Optimization Checklist

• Remove sensitive/unnecessary fields from responses
• Implement sparse fieldsets
• Add ETag/Last-Modified headers
• Enable gzip/brotli compression
• Use pagination for collections
• Eager load to prevent N+1 queries
• Monitor with APM tools

Best Practices

• Cache immutable resources aggressively
• Use short TTL for frequently changing data
• Invalidate cache on writes
• Compress responses >1KB
• Profile before optimizing