fast_json - High-Performance MQL5 JSON Library

"If your JSON parser needs recursion, you're doing it wrong."

Overview

fast_json is a production-grade, high-performance JSON library for MQL5, engineered for scenarios where I/O throughput and memory efficiency are paramount.

Unlike standard libraries that fragment the heap with thousands of small object allocations, fast_json employs a tape-based zero-allocation memory model. It parses JSON directly into a contiguous integer array (the "tape"), enabling it to process gigabytes of data with minimal overhead and zero garbage collection pressure.

Key Features

• 🚀 Zero-Alloc Tape Architecture: Parses the entire JSON into a single contiguous integer array. No objects are created during parsing.
• ⚡ SWAR Acceleration: Uses Simulated 64-bit SWAR (SIMD within a Register) to scan 8 bytes at a time for structural characters, significantly reducing branch misprediction.
• 🛡️ Stack-Safe Iterative Parser: Implemented as a finite state machine. Zero recursion. Immune to stack overflow from deeply nested JSONs.
• 🔧 Handle-Based Navigation: Data access via lightweight CJsonNode structs that point to the tape. Copying nodes is free.
• 💾 High-Throughput I/O: Optimized for rapid Read/Write operations, making it ideal for LLM integration, REST API consumption, and large dataset processing.

Performance

Metric	fast_json	Standard Libs
Allocation Strategy	1 contiguous block (Tape)	N objects per node
Recursion Depth	Unlimited (Heap stack)	Limited (Call stack)
Read/Write Speed	EXTREME (300MB/s+ Est.)	LOW
Memory Fragmentation	Near Zero	High

Installation instructions

OPTION A: Via KnitPkg (recommended)

Prerequisites

To use json_fast in your KnitPkg project, you will need:

1. MetaTrader 5 installed.
2. KnitPkg CLI: The KnitPkg package manager for MetaTrader. If you don't have it, you can install it by following the instructions in the KnitPkg documentation.

Installing as a dependency

Execute the following command in your project directory:

kp add @14134597/fast_json
kp install

OPTION B: Manual installation

Simply download the header file knitpkg/include/14134597/fast_json/fast_json.mqh into your MetaTrader Include/ directory or put this header along with your other source mql files.

Usage

Parsing

#include "../knitpkg/include/14134597/fast_json/fast_json.mqh"

CJson toolkit;
string json = "{\"price\": 1.2345, \"currency\": \"EURUSD\"}";

if (toolkit.Parse(json)) {
    // Zero-copy access
    double price = toolkit["price"].ToDouble();
    string curr  = toolkit["currency"].ToString();
    Print(curr, ": ", price);
} 

Building & Serializing

CJsonBuilder builder;
builder.Obj()
       .Key("signal").Val("buy")
       .Key("volume").Val(0.1)
       .EndObj();

string payload = builder.Build();
// Result: {"signal":"buy","volume":0.1}

Why fast_json?

Because typical MQL5 libraries were designed for configuration files, not high-throughput data streams. fast_json bridges that gap.

Running unit tests with KnitPkg

You can execute kp get to query the KnitPkg Registry for metadata and automatically download/build the latest stable version of fast_api.

Example (run from your MetaTrader Data Folder root):

cd "C:\Users\username\AppData\Roaming\MetaQuotes\Terminal\<TERMINAL_ID>"

kp get mql5 @14134597/fast_json

In Metatrader, refresh the Navigator and then run the unit test scripts under Scripts/fast_json/bin

License

MIT.