Open-source alternatives to Java

RapidJSON is a high-performance C++ library used for parsing and generating JSON data. It provides both document object model and stream-based interfaces to transform JSON strings into structured data and vice versa. The library includes a JSON schema validator to verify that documents conform to predefined rules and a Unicode transcoder for converting strings between UTF-8, UTF-16, and UTF-32 encodings. It also supports relaxed parsing for non-standard JSON containing comments or trailing commas. Additional capabilities cover JSON pointer navigation for locating specific values and string s

orjson is a high-performance Python library for serializing and deserializing JSON data. It functions as both a JSON parsing library and a serialization engine, converting data between native Python objects and UTF-8 encoded bytes. The project provides specialized support for converting complex Python data structures, including dataclasses, datetime objects, and NumPy arrays and scalars, into JSON format. It also allows for the insertion of pre-serialized JSON blobs into documents to maintain processing speed. The library includes capabilities for memory-efficient deserialization through key

easyjson is a high-performance JSON serializer and memory-optimized parser for Go. It provides a reflectionless code generator that creates static Go methods for marshaling and unmarshaling data, eliminating the need for runtime reflection to improve execution speed. The library reduces CPU and memory overhead through several optimization strategies. It employs a system of reusable memory buffer pools to minimize heap allocations and garbage collection pressure. Additionally, it utilizes string interning to deduplicate repeated values and zero-copy string referencing to point to existing buff

This project is a framework for the efficient serialization and deserialization of data structures. It provides a unified, macro-based interface that automates the conversion of complex internal objects into standardized formats and reconstructs them from raw input streams or buffers. By leveraging compile-time code generation, the library minimizes manual implementation overhead while ensuring consistent logic across diverse data types. The framework distinguishes itself through a format-agnostic data model and a visitor-based parsing architecture that decouples data structures from specific

HandyJSON is a Swift JSON serialization library and data mapper. It functions as an object mapper that converts JSON data into typed Swift models and transforms Swift objects back into JSON strings for storage or transmission. The library uses reflection to automatically map JSON keys to object properties and supports custom mapping metadata to resolve naming differences between APIs and code. It provides capabilities for extracting values from deep nested paths within a JSON structure and supports the transformation of complex types such as dates and URLs. The framework handles both the des

simdjson is a high-performance JSON parser that utilizes SIMD instructions to process gigabytes of data per second. It functions as a SIMD JSON parser, a multithreaded NDJSON processing library, a UTF-8 validation engine, and a tool for JSON minification and string building. The project focuses on high-throughput data processing, enabling the ingestion of massive JSON volumes and the verification of UTF-8 encoding standards. It includes dedicated capabilities for constructing JSON strings with optimized memory usage and removing unnecessary whitespace from documents to reduce file size. The

Ultrajson is a high-performance Python JSON library and C-based parser designed to minimize parsing overhead. It provides a C implementation of the JSON specification to enable fast encoding and decoding of data. The project functions as a concurrent JSON processor, supporting multi-threaded serialization and deserialization to increase data throughput and prevent blocking execution. Its capabilities cover Python data serialization and high-performance JSON processing for real-time data pipelines. This includes parsing JSON data and serializing native objects into JSON strings.

yyjson is a high-performance C library for parsing, serializing, and manipulating JSON data structures. It functions as a memory-efficient data tool that utilizes custom memory pools and contiguous block allocation to minimize fragmentation and overhead. The project distinguishes itself as a SIMD JSON processor, using hardware-accelerated vector instructions for rapid string validation and parsing. It provides a toolkit for querying, modifying, and patching nested JSON objects and arrays through pointer-based access and path expressions. The library covers a broad range of data manipulation

This project is a Protocol Buffers Go compiler and code generation framework that translates schema definitions into optimized Go structures and reflection-free serialization methods. It includes a gRPC service generator for producing client and server communication code and a serialization performance toolkit for generating automated benchmarks and test suites. The framework features a plugin-based system for transforming data definitions into source code with custom field mapping and struct tag injection. It allows for custom type mapping and struct type overriding to link data fields to sp

node-fs-extra is a Node.js file system extension that provides a set of additional methods to simplify common file and directory operations. It functions as a recursive directory manager, a JSON file processor, and a file asset manipulator, extending the standard library to provide high-level utilities for managing assets on disk. The project distinguishes itself through recursive capabilities, such as duplicating or removing nested folder structures and ensuring that all missing parent directories are automatically generated when creating files or symbolic links. It also integrates a JSON se

RapidJSON is a header-only C++ library designed for high-performance parsing, generation, and manipulation of JSON data. It functions as a dual-mode engine, providing both an in-memory document object model for tree-based manipulation and a stream-based interface for event-driven processing. The library is built to minimize memory footprint and maximize execution speed, making it suitable for resource-constrained environments. The library distinguishes itself through advanced memory management and optimization techniques, including in-situ parsing that modifies input buffers directly to elimi

Gson is a Java library designed for the serialization and deserialization of objects into structured text formats. It functions as a reflection-based data mapper, inspecting class structures at runtime to automatically convert memory-resident objects into data representations and reconstruct them back into typed language objects. The library distinguishes itself through a modular type-adapter pattern that allows for custom conversion rules for complex or nested structures. It also provides robust support for production environments by generating build-time metadata and configuration rules, wh

Ajv is a high-performance data validation framework that compiles JSON schemas into optimized, standalone JavaScript functions. By transforming declarative schema definitions into executable code, it eliminates runtime interpretation overhead and provides a secure, efficient way to enforce data integrity across both browser and server environments. The library distinguishes itself through its focus on performance and type safety. It employs advanced compilation techniques, including abstract syntax tree optimization and function caching, to ensure rapid validation. Beyond standard checks, it

Sonic is a high-performance Go JSON serialization library that provides tools for encoding and decoding native data structures. It functions as a JIT-accelerated encoder, a JSON AST parser, a stream processor, and a lazy decoder. The project utilizes just-in-time machine code generation to optimize the encoding of large data schemas and employs a JIT assembler to maximize serialization and deserialization speeds. It features a precompiled schema warmup process to prevent latency spikes during initial execution and leverages SIMD hardware instructions for accelerated parsing. The library cove

Jackson is a Java data binding framework and multi-format data serializer used to translate data structures into native language objects. It functions as a JSON data binding library and a streaming parser that reads and writes data as discrete tokens to process large datasets with minimal memory. The project distinguishes itself through a bytecode serialization accelerator that replaces standard reflection with generated bytecode to increase data binding speed. It employs a module-based extensibility model to support a wide range of formats beyond JSON, including XML, YAML, CSV, TOML, and bin

SwiftyJSON is a Swift JSON parsing library and data wrapper designed to simplify the reading and manipulation of JSON structures. It provides a toolkit for converting raw JSON strings into structured formats without requiring manual type casting or optional chaining for every value. The library focuses on simplifying nested data extraction through subscript-based value access and recursive data resolution. It ensures optional-safe value retrieval by returning default empty values instead of crashing when encountering missing keys or out-of-bounds array indices. The project includes capabilit

cJSON is a lightweight library for parsing, creating, and modifying JSON data structures within C applications. It provides a comprehensive set of utilities for transforming raw text into navigable objects, manipulating data fields within collections, and serializing complex structures into formatted or unformatted strings. The library is designed for memory-sensitive and resource-constrained environments, utilizing manual memory management and type-tagged union structures to maintain a minimal footprint. It employs recursive descent parsing and in-place string manipulation to process data ef

Superjson is a lossless JSON serialization library and data transcoder. It converts complex JavaScript and TypeScript data types into strings and metadata to ensure that type identity is preserved during data transfer. The library preserves non-native types such as Dates, Maps, and Sets by splitting values into a JSON-compatible payload and a separate map of type-specific metadata. It utilizes a registry-based mapping system that allows for the definition of custom type handlers to manage third-party data types during serialization and deserialization. This utility supports cross-process dat

flutterrustbridge is a code generation tool that automatically creates type‑safe Dart bindings for Rust functions, enabling direct cross‑language calls between Flutter and a Rust backend. It provides an async FFI adapter that transforms synchronous Rust functions into Dart async methods with background thread management, a cross‑language object manager that wraps persistent Rust structs as Dart objects preserving state across calls, and trait object interop that converts Rust traits into Dart abstract classes for seamless bidirectional use. The project handles the full lifecycle of integrat

MessagePack-CSharp is a high-performance binary serializer for .NET that converts C# objects to and from the compact MessagePack format. It uses compile-time source generation to produce AOT-safe formatters and resolvers, eliminating runtime reflection and enabling ahead-of-time compilation scenarios. The serializer encodes object fields as integer indices instead of string keys, producing compact binary output with deterministic field ordering, and provides stack-allocated reader and writer structs for direct encoding and decoding of MessagePack primitives without heap allocations. The libra

Hazelcast is a distributed data platform that combines an in-memory data grid with a stream processing engine to support real-time analytics and event-driven applications. It functions as a partitioned, distributed key-value store that replicates data across cluster nodes to provide low-latency access and high availability. The platform also serves as a distributed SQL query engine, allowing users to execute standard SQL statements against both in-memory datasets and external data sources. What distinguishes Hazelcast is its use of a distributed consensus subsystem to maintain strongly consis

This project provides a React hook for synchronizing component state with browser storage, ensuring data persists across page reloads and browser sessions. It is designed to manage persistent application state while providing hydration-safe initialization to prevent mismatches during the transition from server-side rendering to client-side execution. The library distinguishes itself by including a fallback manager that detects when browser storage is inaccessible, automatically switching to an in-memory state to maintain application continuity. It also supports cross-tab synchronization by li

simdjson is a high-performance, header-only C++ library designed for parsing, querying, and serializing JSON data with minimal memory overhead. It functions as a hardware-aware data processing engine that leverages vector instructions to achieve gigabyte-per-second parsing speeds. By detecting host processor capabilities at runtime, the library automatically selects the most efficient instruction sets to accelerate structural analysis and validation. The library distinguishes itself through a focus on extreme efficiency and resource management. It utilizes memory mapping and padded buffer ali

Typia is a compile-time code generator that transforms TypeScript type annotations into runtime validation, serialization, and schema functions without requiring decorators or separate schema files. It generates optimized validation and serialization code during TypeScript compilation, producing dedicated functions for each type that eliminate runtime schema objects for faster execution. The project extends this core capability into several integrated areas. It generates fully typed client SDKs from NestJS controller source code, keeping server and client types synchronized automatically. It

UltraJSON is a high-performance JSON library and parser written in C with bindings for Python. It provides a fast alternative to standard JSON processing for decoding JSON strings into native data structures and encoding data structures back into JSON strings. The library utilizes a C-based engine to reduce processing latency and increase throughput for JSON generation and parsing. It is designed to accelerate data pipelines and optimize the handling of JSON payloads.

This library is a Java-based tool for enforcing data structure constraints and verifying technical formats against defined schema specifications. It functions as a processing utility that parses complex data structures while managing external schema references and circular dependencies. The engine distinguishes itself through an immutable processor design that enables thread-safe, concurrent validation without requiring external synchronization. It employs arbitrary-precision arithmetic to evaluate numeric constraints, preventing common floating-point rounding errors, and utilizes character-l

Templ is a type-safe HTML templating engine and UI framework for Go. It provides a system for building reusable HTML components that compile into Go code for server-side rendering, ensuring type safety and compile-time validation of data and logic. The project features a dedicated language server that provides autocomplete and syntax validation for template files within supported code editors. It employs compile-time code generation to transform a custom template language into Go source code, enabling the creation of modular HTML fragments and logic blocks. The framework includes automated s