The Redundant Data Tax
In data-dense B2B SaaS platforms at Smart Tech Devs, clients constantly poll your API for updates. Imagine a dashboard making a GET /api/system-config request every 60 seconds. The payload is 200KB of JSON. If the configuration hasn't changed in three days, your server is spending CPU cycles serializing data, and you are paying AWS egress fees to transmit the exact same 200KB file 1,440 times a day per user.
Basic Redis caching speeds up the database query, but it doesn't stop the payload from traveling over the network. To eliminate network bloat entirely, your API must leverage the browser's native HTTP cache using ETags and the Stale-While-Revalidate directive.
The Solution: 304 Not Modified
An ETag (Entity Tag) is a cryptographic hash (like an MD5 checksum) of the response body. When the server sends the JSON, it includes the ETag in the header.
