Here’s a simple, step-by-step explanation of why this happens and how to fix it.
Why is JSON serialization so slow?
Your server has some data in memory (like a huge list of products, each with name, price, description, reviews, images, etc.).
JSON is the common text format everyone understands (looks like { "name": "Shirt", "price": 29.99, ... }).
Turning that big Python (or whatever language) object into one long JSON string takes a lot of CPU work, especially if the object is massive.
The default JSON tool in many languages (like Python’s built-in json module) is not very fast for huge data.
Best ways to speed it up (in order of simplicity)
Make the data smaller first (easiest and biggest win)
Ask: Does the person really need ALL the information?
Let the client (the app or website) choose only the fields they want.
Example:
fields=id,name,price (this is called sparse fieldsets or projections).
If it’s a long list (1000 products), don’t send everything at once. Use pagination — send only 20 or 50 items, and give a “next page” link.
Result: Much less data to convert → serialization becomes way faster.
Use a faster JSON toolStop using the slow default JSON library.
Switch to super-fast ones like orjson, simdjson, or jsoniter.
These are often 5–10 times faster because they are written in faster languages (like Rust or C) or use clever tricks with modern CPUs.
In many cases, you can just change one line of code and get big speed improvements.
Cache the final JSON (great when data doesn’t change often)If the same request is made many times (e.g., product catalog that updates only once a day),
don’t keep converting to JSON every time.
Convert it to JSON once, then store the ready-made JSON string in a fast cache like Redis.
Next time someone asks, just grab the cached JSON and send it instantly — no serialization needed.
Important: Cache the JSON string, not the original data object.
Stream the response instead of building one giant stringNormally, the server builds the entire huge JSON in memory first, then sends it.
With streaming, it starts writing and sending pieces of JSON as soon as they’re ready (like pouring water continuously instead of filling a big bucket first).
Benefits:Uses less memory.
The client (browser or app) starts receiving and showing data earlier — feels much faster to the user.
Switch to a better format if possible (more advanced)JSON is human-readable but not the most efficient.
If the client (mobile app, another service, etc.) can accept it, use binary formats like:Protobuf (Protocol Buffers)
MessagePack
These are smaller in size and much faster to serialize and deserialize on both sides.
Many companies use gRPC (which is built on Protobuf) for communication between their own microservices.